United States Department of Agriculture 

Biological

Control

TECHNOLOGY TRANSFER 

Biology and Biological control of

dalmatian and yellow toadflax

Sharlene E. Sing, Rosemarie A. De Clerck-Floate, Richard W. Hansen, 

Hal Pearce, Carol Bell Randall, Ivo Toševski, and Sarah M. Ward 

FHTET-2016-01 Forest Health Technology Enterprise 3rd Edition Forest Service Team Morgantown, WV July 2016 
The Forest Technology Enterprise Team (FHTET) was created in 1995 

by the Deputy Chief for State and Private Forestry, USDA Forest Service, 

to develop and deliver technologies to protect and improve the health 

of American forests. This manual was published by FHTET as part of 

the technology transfer series. 

http://www.fs.fed.us/foresthealth/technology/

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or approval by the U.S. Department of Agriculture or the Forest Service of any product 

or service to the exclusion of others that may be suitable. 

CAUTION:

PESTICIDES This publication/database reports research involving pesticides. It does not contain 

recommendations for their use, nor does it imply that the uses discussed here 

have been registered. All uses of pesticides must be registered by appropriate 

State and/or Federal agencies before they can be recommended. 

CAUTION: Pesticides can be injurious to humans, domestic animals, desirable plants, 

and fish or other wildlife—if they are not handled or applied properly. Use all pesticides 

selectively and carefully. Follow recommended practices for the disposal of surplus 

pesticides and pesticide containers. 

How to cite this publication:

Sing, S.E., R. De Clerck-Floate, R.W. Hansen, H. Pearce, C.B. Randall, I. Toševski, and S.M. 

Ward. 2015. Biology and Biological Control of Dalmatian and Yellow Toadflax. USDA Forest 

Service, Forest Health Technology Enterprise Team, Morgantown, West Virginia. FHTET-2015-03. 

Cover photos (L to R): Dalmatian toadax (K. George Beck & James Sebastian, Colorado 

State University); yellow toadax (Linda Wilson, University of Idaho); (Center top to bottom): 

Mecinus spp. adult (Bob Richard, USDA APHIS PPQ ); Calophasia lunula (Laura Parsons & Mark 

Schwarzländer, University of Idaho); Rhinusa linariae (Bob Richard, USDA APHIS PPQ) 

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Printed on recycled paper
Biology and Biological control of 

dalmation and yellow toadflax 

Sharlene E. Sing, Research Entomologist 

USDA Forest Service, Rocky Mountain Research Station 

1648 South 7th Avenue - MSU Campus, Bozeman, MT 

ssing@fs.fed.us 

Rosemarie A. De Clerck-Floate, Research Scientist 

Weed Biological Control, Lethbridge Research Centre 

Agriculture and Agri-Food Canada, Lethbridge, Alberta, Canada 

rosemarie.declerck-oate@agr.gc.ca 

Richard W. Hansen, Entomologist 

USDA Animal and Plant Health Inspection Service 

Plant Protection and Quarantine Center for Plant Health Science and Technology 

2301 Research Blvd., Suite 108, Fort Collins, CO 

Richard.W.Hansen@aphis.usda.gov 

Hal Pearce, Natural Resource Specialist 

USDA Forest Service, Rocky Mountain Region 2 Invasive Species/Pesticide Use Coordinator 

220 East Market Street Meeker, CO 

hpearce@fs.fed.us 

Carol Bell Randall, Entomologist 

USDA Forest Service, Forest Health Protection 

2502 E. Sherman Ave, Coeur d’Alene, ID 

crandall@fs.fed.us 

Ivo Toševski, Research Scientist 

Biological Weed Control, CABI, Rue des Grillons 1, CH-2800 Delémont, Switzerland 

tosevski_ivo@yahoo.com 

Sarah M. Ward, Associate Professor – Plant Genetics 

Department of Soil and Crop Sciences 

Colorado State University, Fort Collins, CO 

sarah.ward@colostate.edu 

Original 2005 version by Linda M. Wilson, Sharlene E. Sing, Gary L. Piper, Richard W. Hansen, 

Rosemarie De Clerck-Floate, Daniel K. MacKinnon, and Carol Bell Randall 
Acknowledgments

The content for this second edition was compiled by Rachel L. Winston (MIA Consulting), and the layout was designed 

by Denise E. Binion, USDA Forest Service-FHTET. Todd Neel (USDA FS) contributed to the discussion on toadflax management options in Chapter 5: An Integrated Toadflax Management Program. We thank Peter G. Mason, Agriculture and 

Agri-Food Canada, for assistance with the Canadian regulatory information. Linda Wilson (University of Idaho), Mark 

Schwarzländer (University of Idaho), Daniel K. MacKinnon (Colorado State University), Eric Coombs (Oregon Department of Agriculture), Robert Nowierski (USDA-CSREES), Susan Turner (British Columbia Ministry of Forests), André 

Gassmann (CABI Bioscience), Ruth Hufbauer (Colorado State University), and Gilbert Wilson (Hazelton, British Columbia) contributed to the first edition of this manual, and many of their contributions have been retained in this revision. We 

also thank Alec McClay, Timothy Collier, and Joseph McCaffrey for reviewing the first edition of this manual. We would 

like to thank all of the photographers who granted permission for the use of photos. We also extend our gratitude to Richard Reardon (Forest Service-Forest Health Technology Enterprise Team or FHTET) for producing this guide. 

This third edition of the Biology and Biological Control of Toadaxes has been updated to reect developments in 

toadax biological control since 2009, and expanded to include more information on the history, process, safety, and application of classical biological control of weeds as a component of an integrated weed management 

program. Since the rst edition was published, the taxonomic classication of Dalmatian and yellow toadax 

has been revised, and hybrids of Dalmatian and yellow toadax have been recognized as signicant pests. New 

images have been added to better illustrate identifying characteristics of Dalmatian toadax, yellow toadax, and 

their hybrids. A new section has been included which provides information on how to distinguish plant species 

commonly confused with Dalmatian, yellow, or hybrid toadax plants. The second edition reects updated taxonomic information which divided the toadax stem mining weevil into two distinct species. New images have 

been added to help readers more easily dierentiate biocontrol agent life stages and biocontrol agent damage to 

toadax plants. Biocontrol agent life stages (eggs, larvae, pupae, adults), life cycles, habitat preferences, damage, 

and current status and availability are described in more detail and in tabular form to facilitate identication and 

comparison of biocontrol agents’ life cycles and damage. The chapter on biocontrol implementation has been 

expanded to provide the reader with resources for successfully planning and implementing a toadax biocontrol 

program. A new chapter on integrated toadax management has been added which describes other management tools for toadax (including physical, cultural, and chemical control) and when and how best to integrate 

biological control with other management tools as part of a toadax integrated weed management program. 

For additional copies of this publication, contact: 

Mark Schwarzländer Carol Bell Randall Richard Reardon 

University of Idaho, PSES Dept. USDA Forest Service USDA Forest Service - FHTET 

875 Perimeter Dr., MS 2339 Forest Health Protection 180 Caneld Street 

Moscow, ID 83844-2339 2502 E. Sherman Ave. Morgantown, WV 26505 

208-885-9319 Coeur d’Alene, ID 83814 304-285-1566 

markschw@uidaho.edu 208-769-3051 rreardon@fs.fed.us 

crandall@fs.fed.us 
TABLE OF CONTENTS 

CHAPTER 1: INTRODUCTION 1 

Overview .................................................................................................................................................................................... 1 

Classical Biological Control of Weeds ................................................................................................................................... 3 

Code of Best Practices for Classical Biological Control of Weeds .................................................................................... 5 

Biological Control of Toadaxes ............................................................................................................................................ 6 

Integrated Weed Management.............................................................................................................................................. 6 

Is Biological Control of Toadax Right for You? .................................................................................................................. 7 

About this Manual.................................................................................................................................................................... 8 

CHAPTER 2: GETTING TO KNOW TOADFLAXES 11 

Classication ........................................................................................................................................................................... 11 

Dalmatian toadax................................................................................................................................................................. 12 

Classication ...........................................................................................................................................................................................12 

History ......................................................................................................................................................................................................12 

Description ..............................................................................................................................................................................................12 

Biology and Ecology ..............................................................................................................................................................................16 

Habitat ......................................................................................................................................................................................................16 

Distribution .............................................................................................................................................................................................17 

Taxonomic issues ...................................................................................................................................................................................17 

Commonly Confused Species ..............................................................................................................................................................19 

Yellow toadax........................................................................................................................................................................ 20 

Classication ...........................................................................................................................................................................................20 

History ......................................................................................................................................................................................................20 

Description ..............................................................................................................................................................................................20 

Biology and Ecology ..............................................................................................................................................................................24 

Habitat ......................................................................................................................................................................................................25 

Distribution .............................................................................................................................................................................................25 

Commonly Confused Species ..............................................................................................................................................................26 

Hybrid toadax ....................................................................................................................................................................... 28 

Classication ...........................................................................................................................................................................................28 

History ......................................................................................................................................................................................................28 

Description ..............................................................................................................................................................................................28 

Biology and Ecology ..............................................................................................................................................................................31 

Habitat ......................................................................................................................................................................................................32 

Distribution .............................................................................................................................................................................................32 

Toadax Comparison Table .................................................................................................................................................. 34 

CHAPTER 3: BIOLOGY OF TOADFLAX BIOLOGICAL CONTROL AGENTS 35 

Basic Insect Biology................................................................................................................................................................ 35 

Toadax ower-feeding beetle 

Toadax stem-mining weevil 

Toadax seed weevil 

Toadax root-galling weevil 

Toadax defoliating moth 

Toadax Biological Control Agents..................................................................................................................................... 36 

Beetles ......................................................................................................................................................................................................36 

Butteries and Moths ............................................................................................................................................................................36 

Brachypterolus pulicarius ......................................................................................................................................................................38 

Mecinus janthinus & M. janthiniformis ................................................................................................................................................41 

Rhinusa antirrhini & R. neta ...................................................................................................................................................................45 

Rhinusa linariae .......................................................................................................................................................................................49 

Calophasia lunula ...................................................................................................................................................................................52 

Eteobalea intermediella & E. serratella ................................................................................................................................................54 

Toadax root-boring moths 
Comparison Tables .................................................................................................................................................................................60 

Prospective Toadax Biological Control Agents ..............................................................................................................................62 

CHAPTER 4: ELEMENTS OF A TOADFLAX BIOLOGICAL CONTROL PROGRAM 67 

Before You Begin..................................................................................................................................................................... 67 

Determining the Scope of the Problem .............................................................................................................................................67 

Dening Goals and Objectives ............................................................................................................................................................68 

Understanding Toadax Management Options ..............................................................................................................................68 

Developing, implementing and Managing a Toadax Biological Control Program.................................................. 69 

Selecting Biological Control Agent Release Sites .............................................................................................................................69 

Establish goals for your release site.............................................................................................................................................................................................. 69 

Determine site characteristics ........................................................................................................................................................................................................ 69 

Note land use and disturbance factors ....................................................................................................................................................................................... 70 

Survey for presence of biological control agents.................................................................................................................................................................... 70 

Record ownership and access ........................................................................................................................................................................................................ 70 

Choosing the Appropriate Biological Control Agents for Release ................................................................................................71 

Biocontrol agent ecacy ................................................................................................................................................................................................................. 74 

Biocontrol agent availability ........................................................................................................................................................................................................... 74 

Release site characteristics .............................................................................................................................................................................................................. 74 

Obtaining and Releasing Toadax Biological Control Agents........................................................................................................74 

Factors to consider when looking for sources of biological control agents.................................................................................................................. 75 

Collecting Toadax Biological Control Agents ......................................................................................................................................................................... 75 

Collection methods................................................................................................................................................................................................................ 76 

Tray sampling ............................................................................................................................................................................................................... 76 

Hand picking ................................................................................................................................................................................................................ 76 

Aspirating....................................................................................................................................................................................................................... 76 

Sweep netting.............................................................................................................................................................................................................. 78 

Transferring agent-infested plant material ....................................................................................................................................................... 79 

Sorting ............................................................................................................................................................................................................................ 79 

Collection methods by species .......................................................................................................................................................................................... 80 

Toadax ower-feeding beetle (Brachypterolus pulicarius).......................................................................................................................... 80 

Toadax defoliating moth (Calophasia lunula)................................................................................................................................................. 80 

Toadax stem-mining weevils (Mecinus janthinus/M. janthiniformis) ...................................................................................................... 80 

Toadax seed-galling weevil (Rhinusa antirrhini)............................................................................................................................................ 81 

Toadax root-galling weevil (Rhinusa linariae)................................................................................................................................................. 82 

Release Containers for Toadax Biological Control Agents ................................................................................................................................................. 82 

Transporting Toadax Biological Control Agents.................................................................................................................................................................... 83 

Keep the containers cool at all times................................................................................................................................................................... 83 

Transporting short distances.................................................................................................................................................................................. 83 

Shipping long distances........................................................................................................................................................................................... 83 

Other factors to consider ......................................................................................................................................................................................... 84 

Common packaging mistakes................................................................................................................................................................................ 84 

Purchasing Toadax Biological Control Agents........................................................................................................................................................................ 85 

Releasing Toadax Biological Control Agents .......................................................................................................................................................................... 85 

Establish permanent location marker ................................................................................................................................................................. 85 

Record geographical coordinates at release point using GPS.................................................................................................................... 85 

Prepare map.................................................................................................................................................................................................................. 85 

Complete relevant paperwork at site .................................................................................................................................................................. 86 

Set up photo point ..................................................................................................................................................................................................... 86 

Release as many agents as possible..................................................................................................................................................................... 86 

Regulations for the Transfer of Toadax Biological Control Agents.................................................................................................................................. 88 

Documenting, Monitoring and Evaluation a Biological Control Program ...................................................................................89 

The Need for Documentation......................................................................................................................................................................................................... 89 

Information Databases...................................................................................................................................................................................................................... 89 

Monitoring Methods.......................................................................................................................................................................................................................... 90 

Assessing biological control agent populations.............................................................................................................................................. 90 

Assessing the status of toadaxes and co-occurring plants ....................................................................................................................... 94 

 Qualitative vegetation monitoring ............................................................................................................................................................ 94 

 Quantitative vegetation monitoring ......................................................................................................................................................... 94 

Assessing impacts on nontarget plants.............................................................................................................................................................. 95 

CHAPTER 5 : AN INTEGRATED TOADFLAX MANAGEMENT PROGRAM 99 

Introduction............................................................................................................................................................................. 99 

Components of Integrated Weed Management Programs ..........................................................................................100 

Education & Outreach .........................................................................................................................................................................................100 
Inventory & Mapping ..........................................................................................................................................................................................101 

Prevention ............................................................................................................................................................................................................101 

 EDRR ...........................................................................................................................................................................................................................................102 

Weed Control Activities.......................................................................................................................................................................................103 

 Biological Control ..................................................................................................................................................................................................................103 

 Physical Treatment .................................................................................................................................................................................................................103 

 Hand pulling ..................................................................................................................................................................................................................103 

 Mowing ............................................................................................................................................................................................................................104 

Tilling ................................................................................................................................................................................................................................105 

 Cultural Practices ....................................................................................................................................................................................................................105 

 Flooding and Burning ................................................................................................................................................................................................105 

 Grazing ............................................................................................................................................................................................................................106 

 Seeding competitive species ...................................................................................................................................................................................107 

 Chemical Control ..................................................................................................................................................................................................................108 

GLOSSARY 115 

SELECTED REFERENCES 120 

Chapter 1: Introduction.......................................................................................................................................................120 

Chapter 2: Getting to Know Toadaxes............................................................................................................................120 

Chapter 3: Biology of Toadaxes Biological Control Agents ........................................................................................122 

Chapter 4: Elements of a Toadaxes Biocontrol Program ............................................................................................124 

Chapter 5: An Integrated Toadaxes Management Program ......................................................................................125 

APPENDICES 129 

Appendix I: Troubleshooting Guide: When Things Go Wrong .....................................................................................129 

Appendix II: Sample Biological Control Agent Release Form .....................................................................................130 

Appendix III: Toadax Standardized Impact Monitoring Protocol .............................................................................132 

Appendix IV: General Toadax Biological Control Agent Monitoring Form ............................................................136 

Appendix V: Toadax Qualitative Monitoring Form .....................................................................................................138 

Appendix VI: Toadax Quantitative Monitoring Form ..................................................................................................139 

BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 1: Introduction 1 

CHAPTER 1: INTRODUCTION 

Overview 

Dalmatian toadflax, Linaria dalmatica (L.) Mill., and yellow toadflax, Linaria vulgaris Mill., 

are exotic weeds of rangeland, grassland, forests, and cropland. Both Dalmatian and yellow 

toadflax are short-lived perennial forbs that are easily recognized by their yellow snapdragonlike flowers (Figure 1a, 1b). Both species propagate by seed and vegetatively from shoots that 

arise either from lateral rhizomes (Dalmatian toadflax) or from buds developing on their roots 

(yellow toadflax). Dalmatian toadflax is native to southeastern Europe while yellow toadflax 

is considered to be native to Europe and Asia. Hybrids of Dalmatian and yellow toadflax 

have been found throughout northwestern USA (Figure 1c; hybrids are discussed further in 

Chapter 2 of this manual). Although several exotic toadflax species have been intentionally or 

accidentally introduced to North America, these two species and their hybrids are by far the 

most common and problematic for land managers, and are the focus of this manual. The use of 

“toadflaxes” throughout this manual encompasses both Dalmatian and yellow toadflax, as well 

as their hybrids. 

a b c 

Figure 1. Toadax plants a. Dalmatian toadax (K. George Beck & James Sebastian, Colorado State 

University); b. yellow toadax (Tiany Wax, Washington State University Extension), c. hybrid 

toadax (center) between yellow toadax (left) and Dalmatian toadax (right) (Elizabeth 

Goulet, Cornell University)(a,c bugwood.org) 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

2 Chapter 1: Introduction

Dalmatian and yellow toadflax were introduced to North America by the 1800s, likely as 

ornamental plants, and for use in fabric dye and folk remedies. Both species are now present 

throughout much of temperate North America. Yellow toadflax occurs in all continental states, 

all 10 Canadian provinces, and two Canadian territories (Figure 2a), while Dalmatian toadflax 

is mostly absent in the southeastern USA, Alaska, and the Canadian territories (Figure 2b). The 

widespread distribution of both species in North America likely began with their sentimental 

and medicinal value to early settlers, and continued to increase with their popularity as hardy 

ornamental plants coupled with their highly invasive nature. Exotic toadflaxes continue to be 

sold as nursery stock in the USA, advertised as “butter and eggs,” “wild snapdragon,” and 

“Jacob’s ladder”; toadflax seed is sometimes still a component of wildflower seed mixes. The 

sale of these two species is now illegal in states where they are classified as regulated plants 

or noxious weeds. Hybrids of yellow and Dalmatian toadflax were recently confirmed to be 

present in five western states (Figure 2c). 

a b c 

Figure 2. North American distribution maps of a. yellow toadax; b. Dalmatian toadax (a,b USDA 

PLANTS Database, EDDMapS); hybrids of yellow and Dalmatian toadax (Sarah M. Ward, 

unpublished data) 

Yellow and Dalmatian toadflax are known to thrive particularly well in disturbed, open habitats, 

especially in areas characterized by dry summers. Dalmatian toadflax is most commonly found 

on well-drained, coarse-textured soils in disturbed or otherwise degraded sites, such as roadsides, 

abandoned lots and fields, gravel pits, forest or pasture clearings, overgrazed or deteriorated 

rangelands, and along railroad tracks. Because Dalmatian and yellow toadflax compete 

aggressively for light, water, and nutrients, both toadflaxes can displace native and/or more 

desirable plant species in natural areas. Although yellow toadflax is typically associated with 

more moist and fertile sites, it can invade higher elevations (e.g. alpine meadows), and unlike 

Dalmatian toadflax, affects cropland. Consequently, yellow toadflax is a serious management 

concern on both cultivated and uncultivated sites. Large yellow toadflax infestations have 

caused economic injury to crops as diverse as grain, oil seed, berries/small fruits, and oil mint. 

Economic injury associated with hybrid toadflax infestations is thus far unknown. 

Successful management of toadflaxes is an intensive process due to their robust root systems 

and abundant seed production. Hand-pulling small, individual toadflax plants can be an 

effective control strategy if repeated for several years. Pulling large plants is more difficult and 

may exacerbate the problem if viable root fragments are left behind to generate new shoots. 

Repeated mowing can reduce toadflax vigor and seed production, but may similarly exacerbate 

the problem by triggering re-growth and spreading seeds. Tilling is effective only if repeated 

regularly throughout the growing season and for multiple years in a row, but it is generally 

not feasible in many settings where toadflax infestations occur. Infrequent tilling increases 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 1: Introduction 3 

toadflax infestations because it facilitates the development of new shoots from fragmented 

roots. Burning is largely ineffective for toadflax control as it typically fails to kill enough of the 

roots to prevent re-sprouting, and often favors the re-establishment and growth of toadflaxes 

over less competitive species. 

Toadflaxes produce secondary compounds known to deter herbivory, which may make them 

initially less attractive for grazing; however, with sufficient exposure, acceptance and even 

preference for grazing on Dalmatian and yellow toadflax typically increase. Livestock and 

wildlife have been observed browsing toadflaxes, and cattle and sheep have both been “trained” 

successfully to suppress Dalmatian and yellow toadflax infestations. Grazing toadflaxes can be 

an effective management strategy under the right circumstances, but it can be difficult and/or 

time-consuming to implement strategically, and may have negative, long-term consequences 

for plant communities. Herbicides can provide satisfactory short-term control of small toadflax 

infestations, but treatments generally need to be repeated regularly for lasting results. Dalmatian 

toadflax typically requires the use of a surfactant to aid penetration of herbicides into the waxy 

leaves. Yellow toadflax is thought to be more difficult to control with herbicides than Dalmatian 

toadflax. For both species, and their hybrids, herbicides can be impractical and uneconomical 

against very large infestations and may have negative, long-term effects on plant communities. 

Due to the difficulties in managing toadflaxes throughout their invaded range, a biological 

control program was initiated in the 1950s. This manual discusses the biological control of 

toadflaxes in North America, within the larger context of an integrated toadflax management 

strategy. 

Classical Biological Control of Weeds 

Most invasive plants in the United States are not native to North America; they arrived with 

immigrants, through commerce, or by accident from different parts of the world. These nonnative plants are generally introduced without their natural enemies, the complex of organisms 

that feed on or attack the plant in its native range. A lack of natural enemies is thought to be 

one reason plant species become invasive pests when introduced to areas outside of their native 

range. 

Biological control of weeds (also called “biocontrol”) of weeds is the deliberate use of living 

organisms to limit the abundance of a target weed. In this manual, biological control refers to 

“classical biological control,” which reunites host-specific natural enemies from the weed’s 

native range with the target weed in its introduced range. Natural enemies used in classical 

biological control of weeds include different organisms, such as insects, mites, nematodes, and 

pathogens. In North America, most weed biological control agents are plant-feeding insects, of 

which beetles, flies, and moths are among the most commonly used. 

Biological control agents may attack a weed’s flowers, seeds, roots, foliage, and/or stems. 

Effective biological control agents seldom kill weeds outright, but work with other stressors 

such as moisture or nutrient shortages to reduce vigor and reproductive capability, or facilitate 

secondary infection from pathogens—all of which compromise the weed’s ability to compete 

with other plant species. Once established, root- and crown-feeding biocontrol agents are 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

4 Chapter 1: Introduction

usually more effective against perennial plants that primarily spread by root buds. Flowerand seed-feeding biocontrol agents are typically more useful against annual or biennial plants 

that spread only by seed. Regardless of the plant part attacked by biocontrol agents, the aim is 

always to reduce populations of the target weed. 

There are advantages and disadvantages to biological control of weeds as a management tool 

(Table 1). 

Table 1. Advantages/disadvantages of classical biological control as a weed management tool. 

Advantages Disadvantages 

Target specificity Will not work on every weed in every setting 

Continuous action Permanent; cannot be undone 

Long-term cost-effective; can provide 

sustained control at the landscape scale 

Funding and testing candidate biocontrol 

agents is expensive; measurable impact may 

take years or even decades to materialize 

Integrates well with other control methods Approved biocontrol agents are not available 

for all exotic weeds 

Generally environmentally benign Like all weed control methods, “nontarget” 

effects are possible, but pre-release testing 

reduces the risks 

Self-dispersing, even into rough or difficult to 

access terrain 

Unpredictable level of control; generally does 

not eliminate weed 

To be approved for release in North America, weed biocontrol agents must be host-specific, 

meaning they must feed and develop only on the target weed, or in limited cases, on a few closely 

related plant species. They must never feed on any crop or protected plant species; attack on 

ornamental plants may be minimally tolerated and is evaluated on a case-by-case basis. Rigorous 

testing is required to confirm that biocontrol agents are host specific and effective. Potential 

biocontrol agents often undergo five or more years of testing to ensure that rigid host specificity 

requirements are met, and results are vetted at a number of stages in the approval process. 

The United States Department of Agriculture’s Animal and Plant Health Inspection Service - Plant 

Protection and Quarantine (USDA-APHIS-PPQ) is the federal regulatory agency responsible 

for providing testing guidelines and authorizing the importation of biocontrol agents into the 

USA. The Canadian Food Inspection Agency (CFIA) serves the same regulatory role in Canada. 

Federal laws and regulations are in place to identify and avoid potential risks to native and 

economically valuable plants and animals that could result from exotic organisms introduced to 

manage weeds. The Technical Advisory Group (TAG) for Biological Control Agents of Weeds 

is an expert committee with representatives from USA federal regulatory, resource management, 

and environmental protection agencies, and regulatory counterparts from Canada and Mexico. 

TAG members review all petitions to import new biocontrol agents into the USA, and make 

recommendations to USDA-APHIS-PPQ regarding the safety and potential impact of prospective 

biocontrol agents. Weed biocontrol researchers work closely with USDA-APHIS-PPQ and TAG 

to accurately assess the environmental safety of potential weed biocontrol agents and programs. 

In addition, some states in the USA have their own approval process to permit field release of 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 1: Introduction 5 

weed biocontrol agents. In Canada, the Biological Control Review Committee (BCRC) draws 

upon the expertise and perspectives of Canadian-based researchers (e.g. entomologists, botanists, 

ecologists, weed biological control scientists) from academic, government, and private sectors 

for scientific review of petitions submitted to the CFIA. The BCRC reviews submissions for 

compliance with the North American Plant Protection Organization’s (NAPPO) Regional 

Standards for Phytosanitary Measures (RSMP) No. 7. The BCRC also reviews submissions to 

APHIS. The BCRC conclusions factor into the final TAG recommendation to APHIS on whether 

to support the release of the proposed agent in the USA. When release of an agent is proposed 

for both the USA and Canada, APHIS and the CFIA attempt to coordinate decisions based on the 

assessed safety of each country’s plant resources. 

Code of Best Practices for Classical Biological Control of Weeds 

Biological control practitioners have adopted the International Code of Best Practices for 

Biological Control of Weeds. The Code was developed in 1999 by delegates and participants 

in the Tenth International Symposium for Biological Control of Weeds to both improve the 

efficacy of, and reduce potential negative impacts from, weed biological control. In following 

the Code, practitioners reduce the potential for causing environmental damage through the use 

of weed biological control by voluntarily restricting biocontrol activities to those most likely 

to result in success and least likely to cause harm. 

International Code of Best Practices for Classical Biological Control of Weeds 

1. Ensure that the target weed’s potential impact justifies release of non-endemic agents

 2. Obtain multi-agency approval for target

 3. Select agents with potential to control target

 4. Release safe and approved agents

 5. Ensure that only the intended agent is released

 6. Use appropriate protocols for release and documentation

 7. Monitor impact on the target

 8. Stop releases of ineffective agents or when control is achieved

 9. Monitor impacts on potential nontargets

 10. Encourage assessment of changes in plant and animal communities

 11. Monitor interaction among agents

 12. Communicate results to public 

Ratified July 9, 1999, by the delegates to the X International Symposium on Biological Control of 

Weeds, Bozeman, MT 

Although weed biological control is an effective and important weed management tool, it does 

not work in all cases and should not be expected to eradicate the target weed. Even in the most 

successful cases, biocontrol often requires multiple years before impacts become noticeable. 

When classical biological control alone does not result in an acceptable level of weed control, 

other weed control methods (e.g. physical, cultural, or chemical control) may be incorporated 

to achieve desired results. For a more in-depth description of all weed control methods in the 

context of toadflax management, please refer to Chapter 5. 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

6 Chapter 1: Introduction

Biological Control of Toadaxes 

Three insect species that likely ‘hitch-hiked’ on yellow toadflax plants imported from Europe 

are now credited with the earliest incidences of biological control of toadflaxes in North 

America. The flower-feeding beetle, Brachypterolus pulicarius, and two seed-feeding weevils, 

Rhinusa antirrhini (formerly Gymnetron antirrhini) and R. neta (formerly Gymnetron netum), 

were first recorded between 1909 and 1957 on yellow toadflax growing in the USA and Canada. 

Following the initiation of the toadflax biocontrol program in the 1950s, five additional species 

were officially screened for safety, suitability, host specificity, and efficacy. 

The first tested and approved toadflax biocontrol agent, the defoliating moth Calophasia lunula 

(Figure 3), was released in Canada in 1962 and subsequently in the USA. During the 1990s, 

four additional toadflax biological control 

agents were approved for release in North 

America, including two root-boring moths 

(Eteobalea intermediella and E. serratella), 

a root-galling weevil (Rhinusa linariae, 

formerly Gymnetron linariae), and a stemmining weevil (Mecinus janthinus). Recently, 

some populations of what was thought to be 

Mecinus janthinus were determined through 

DNA analysis to be composed of a closely 

related, but morphologically indistinguishable 

species, Mecinus janthiniformis. Surveys have 

determined that M. janthiniformis preferentially 

feeds on Dalmatian toadflax and is well 

established throughout the USA Northwest 

and southern British Columbia, Canada. A 

few relatively small-sized populations of M. 

janthiniformis also have been recently found 

established on Dalmatian toadflax in southern 

Alberta. Mecinus janthinus preferentially feeds on yellow toadflax, and while currently more 

rarely encountered than M. janthiniformis, has recently been confirmed as successfully established 

at limited sites in the USA and Canada. 

Integrated Weed Management 

The most effective weed management programs vary weed management activities and control 

methods based on changing weed populations and management objectives over time (termed 

Integrated Weed Management or IWM). Weed management activities available to managers 

include education and prevention, physical (hand pulling, mowing, or tilling), cultural (burning, 

flooding, grazing, or re-seeding), chemical (herbicides), and biological control. IWM relies on 

the development of realistic weed management objectives, accurate weed identification and 

mapping, appropriate control methods, and post-treatment monitoring to ensure current weedmanagement activities are meeting weed-management goals. 

Figure 3. Adult Calophasia lunula, the toadax 

defoliating moth (Laura Parsons & Mark 

Schwarzländer, University of Idaho) 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 1: Introduction 7 

Land managers choose weed control methods that will enable them to achieve their weed 

management goals or objectives in the most cost-effective manner. No single weed control 

method will enable managers to meet their toadflax management goals in all environments or 

instances. Control method(s) employed in IWM will depend on the size and location of the 

infested area and specific management goals (e.g., eradication vs. weed density reduction). 

Very small patches of toadflaxes may be eliminated through a persistent hand-pulling or 

herbicide program, but large infestations will require the use of additional control methods. A 

combination of control methods consistently applied through time may be necessary to attain 

and maintain weed management goals for toadflaxes, especially when they infest large areas. 

Is Biological Control of Toadax Right For You? 

When biological control is successful, biocontrol agents increase in abundance until they 

suppress (or contribute to the suppression of) the target weed. As local target weed populations 

are reduced, their biological control agent populations also decline due to starvation and/or 

dispersal to other target weed infestations. In many biocontrol systems, there are fluctuations 

over time with the target weed becoming more abundant, followed by increases of its biocontrol 

agent, until the target weed/biocontrol agent populations stabilize at a much lower abundance. 

While biocontrol has been successful against toadflaxes at many sites in North America, it is 

not universally effective or appropriate for every toadflax infestation. We recommend that you 

develop an integrated weed management program in which biological control is one of several 

weed management approaches considered. Here are some questions you should ask before you 

begin a biological control program: 

Is my management goal to eradicate the weed or reduce its abundance? 

Biological control does not eradicate target weeds, so it is not a good fit with an eradication 

goal. However, depending on the target weed, biological control agent used, and land use, 

biological control can be effective at reducing the abundance of a target weed to an acceptable 

level. 

How soon do I need results: this season, one to two seasons, or within five to ten years? 

Biological control requires time and patience to work. Generally, it can take one to three years 

after release to confirm that biological control agents are established at a site, and even longer 

for biocontrol agents to cause significant impacts to the target weed. For some weed infestations, 

5-30 years may be needed for biological control to reach its weed management potential. 

What resources can I devote to my weed problem? 

If you have only a small toadflax problem (few infested acres or much smaller), weed control 

methods such as hand pulling and/or herbicide applications, followed by regular monitoring for 

re-growth, may be most effective. These intensive control methods may allow you to achieve 

rapid control and prevent the weed from infesting more area, especially when infestations 

occur in high-priority treatment areas such as travel corridors where the weed is more likely to 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

8 Chapter 1: Introduction

readily disperse. However, if the target weed is well established over a large area, and resources 

are limited, biological control may be the most economical weed control option. 

Is the weed the problem, or a symptom of the problem? 

Invasive plant infestations often occur where desirable plant communities have been or continue 

to be disturbed. Without restoration of a desirable, resilient plant community, and especially if 

disturbance continues, biological control is unlikely to solve your weed problems. 

The ideal biological control program: 

1. is based upon an understanding of the target weed, its habitat, land use and condition, 

and management objectives 

2. is part of a broader integrated weed management program 

3. has considered all weed control methods and determined that biological control is

 the best option based on available resources and weed management objectives 

4. has realistic weed management goals and timelines 

5. includes resources to ensure adequate monitoring of the target weed, the vegetation

 community, and populations of biological control agents 

About This Manual 

This manual provides information on the biology and ecology of Dalmatian toadflax, yellow 

toadflax, their hybrids, and toadflax biological control agents. It also presents guidelines to 

establish and manage biological control agents as part of an integrated toadflax management 

program. 

Chapter 1: Introduction provides introductory information on toadflaxes (including their 

distribution, habitat, and economic impact) and classical biological control. 

Chapter 2: Getting to Know Toadflaxes provides detailed descriptions of the taxonomy, growth 

characteristics and features, invaded habitats, and occurrence of Dalmatian toadflax, yellow 

toadflax, and their hybrids in North America. It also describes how to differentiate toadflaxes 

from look-alike species. 

Chapter 3: Biology of Toadflax Biological Control Agents describes biological control agents of 

toadflaxes, including details on each agent’s native range, original source of releases in North 

America, part(s) of toadflax plants attacked, life cycle, description, host specificity, known 

nontarget effects, habitat preferences, and availability. This chapter is particularly useful for 

identifying biological control agents in the field. 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 1: Introduction 9 

Chapter 4: Elements of a Toadflax Biological Control Program includes detailed information 

and guidelines on how to plan, implement, monitor, and evaluate an effective toadflax biological 

control program. Included are guidelines and methods for: 

• Selecting and preparing biological control agent release sites 

• Collecting, handling, transporting, shipping, and releasing biological control agents 

• Monitoring biocontrol agents and vegetation 

Chapter 5: An Integrated Toadflax Management Program discusses the role of biological 

control in the context of an integrated toadflax management program. 

The Glossary defines technical terms frequently used by those involved in toadflax biological 

control and found throughout this manual. 

References lists selected publications and resources utilized to compile this manual. 

Appendices: 

I. Troubleshooting Guide: When Things Go Wrong 

II. Sample Biological Control Agent Release Form 

III. Toadflax Standardizied Impact Monitoring Protocol 

IV. General Toadflax Biological Control Agent Monitoring Form 

V. Toadflax Qualitative Monitoring Form 

VI. Toadflax Quantitative Monitoring Form 

BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 2: Getting to Know Toadaxes 11 

CHAPTER 2: GETTING TO KNOW TOADFLAXES 

Classication 

It has been suggested that toadflaxes were so 

named because toads liked to hide in their foliage, 

and the shape of toadflax flowers resemble a toad’s 

mouth. The name “toadflax” is applied to several 

closely related plant species. Formerly members of 

the figwort family (Scrophulariaceae), they were 

recently reclassified as members of the plantain 

family (Plantaginaceae). Closely related plants in 

this family include the snapdragons; toadflaxes 

and snapdragons share a unique five-petal flower 

with distinct upper and lower lips, and a long spur 

(Figure 4). 

Dalmatian toadflax, yellow toadflax, and their 

hybrids are in the genus Linaria. There are 

approximately 150 species in this genus, none of 

which are native to North America. Four plant 

species native to North America were previously 

considered to be in Linaria, but have since been 

re-classified to a different genus, Nuttallanthus. 

Approximately 13 Linaria species and hybrids of 

two different pairs of Linaria occur in the USA and 

Canada. All species of Linaria have smooth-margined leaves that attach directly to the stem 

without a supporting stalk (petiole). Linaria flowers are arranged in long clusters at stem tips 

and bloom from the bottom upwards. 

Of the 13 Linaria species present in North America, Dalmatian toadflax [Linaria dalmatica 

(L.) Mill.], yellow toadflax [Linaria vulgaris Mill], and their hybrids are by far the most 

common and problematic for land managers, and are the focus of this manual. The taxonomy 

of Dalmatian toadflax is currently in flux and is described in greater detail later in this chapter. 

a

b

c

Figure 4. Toadax ower diagram a. twopetal upper lip; b. three-petal 

lower lip; c. spur (Javier Martin) 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

12 Chapter 2: Getting to Know Toadaxes

Dalmatian Toadax 

Scientic Name 

Linaria dalmatica (L.) Mill 

Common Names 

Dalmatian toadax, broad-leaved toadax, narrow-leaved toadax 

Classication 

KINGDOM Plantae Plants

 SUBKINGDOM Tracheobionta Vascular plants

 SUPERDIVISION Spermatophyta Seed plants

 DIVISION Magnoliophyta Flowering plants

 CLASS Magnoliopsida Dicotyledons

 SUBCLASS Asteridae

 ORDER Lamiales

 FAMILY Plantaginaceae Plantain family

 GENUS Linaria Linaria

 SPECIES Linaria dalmatica (L.) Mill. Dalmatian toadflax

 SUBSPECIES Linaria dalmatica (L.) Mill. ssp. dalmatica (L.) Mill. 

Linaria dalmatica (L.) Mill. ssp. 

macedonica (Griseb.) D.A. Sutton 

broad-leaved 

Dalmatian toadflax 

narrow-leaved 

Dalmatian toadflax 

History 

Dalmatian toadflax was introduced to eastern North America from southeastern Europe by the 

late 1800s, reportedly as an ornamental plant used by horticulturists in private gardens. Plants that 

escaped cultivation were collected in California in 1920 and Edmonton, Alberta in 1933. 

Description 

At a Glance 

Dalmatian toadflax (Figures 5, 8) is an erect, herbaceous perennial with one or more stems 

growing 1-4 feet tall (0.3-1.2 m) from a deep taproot with lateral roots. Leaves are alternate, 

thick (succulent to leathery), green in color (sometimes blue-green), and often with a waxy 

surface. Leaves are heart-shaped at the base, clasp the stem, and are typically 1-2 inches long 

(2.5-5.0 cm) and nearly as wide. Flowers are bright yellow and snapdragon-like with an obvious 

upper and lower lip and a long spur pointing downward. Each has a fuzzy, yellowish-orange 

throat. Flowers occur in spiked clusters emerging from leaf axils. Each flower produces a round 

capsule holding 60-300 small, somewhat triangular seeds. 

Roots 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 2: Getting to Know Toadaxes 13 

c

Dalmatian toadflax develops taproots that are 

large, contorted, and deep (up to 4-10 feet or 

1.2-3 m in length). Roots have lateral branches 

that can extend over 10 feet (3 m) from the 

parent plant, giving rise to vegetative buds that 

produce new stems. Over time, these shoots 

form their own roots and eventually become 

independent plants. Severed root segments as 

short as 0.4 inches long (1 cm) can develop into 

new plants. 

Stems 

Plants typically grow 1-4 feet tall (0.3-1.2 m) 

and have 1-25 erect stems that are leafy, thickwalled, fibrous and waxy in appearance. Plants 

also produce non-flowering, prostrate stems 

(Figure 6a). Prostrate stems typically persist 

over winter until the following growing season. 

Figure 5. Dalmatian toadax plant (K. George 

Beck & James Sebastian, Colorado 

State University) 

Leaves 

Dalmatian toadflax leaves are long and narrow on seedlings (Figure 6b), but grow significantly 

wider with age. Mature leaves are heart-shaped at the base, clasp the stem, and are typically 

1-2 inches long (2.5-5.0 cm) and nearly as wide. Upper leaves are smaller and oval or lanceshaped. All leaves are alternate, thick, green (sometimes blue-green), often waxy, and have 

multiple prominent veins. 

a b

Figure 6. Dalmatian toadax a. erect and prostrate stems; b. seedlings; c. mature leaves (a-c Linda 

Wilson, University of Idaho, bugwood.org) 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

14 Chapter 2: Getting to Know Toadaxes

a

Flowers 

Flowers are bright yellow and snapdragon-like with an obvious upper and lower lip and a 

long spur pointing downward. Each flower is 0.8-1.6 inches long (2-4 cm) and has a fuzzy, 

yellowish-orange throat (Figure 7a). Flowers occur in spiked clusters emerging from leaf axils. 

Flowering occurs throughout the summer. 

Fruits and Seeds 

Each flower produces a round capsule fruit (Figure 7b) that is 0.2-0.4 inches long (0.5-1.0 cm) 

and 0.2-0.3 inches wide (0.5-0.75 cm). Each capsule contains 60-300 seeds. Seeds are small, 

triangular or pyramidal in shape, rough textured, minimally winged, and approximately 0.04 

inches long (1 mm) (Figure 7c). A mature plant can produce up to 500,000 seeds annually. 

b c

Figure 7. Dalmatian toadflax a. flower (Bonnie Million, National Park Service); b. fruits (Linda Wilson, 

University of Idaho); c. seeds (Steve Hurst, USDA NRCS PLANTS database) (a-c bugwood. 

org) 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 2: Getting to Know Toadaxes 15 

Figure 8. Line drawing of Dalmatian toadax key traits of a. plant; b. ower; c. fruit; d. seeds 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

16 Chapter 2: Getting to Know Toadaxes

a

Biology and Ecology 

Dalmatian toadflax spreads by seeds and root fragments. Seeds are dispersed fall through winter, 

and typically spread by humans and animals. Seeds can be caught on motorized equipment, mud 

on tires or clothing, hay, or animal fur. Because seeds ingested by animals often remain viable upon 

defecation, livestock, birds, elk, and deer grazing toadflax fruits in autumn is one of the primary 

modes of toadflax long distance seed dispersal. Many Dalmatian toadflax seeds germinate within 

one year; however, the soil seed bank can at times yield seedlings ten years after seed drop. The 

highest rates of germination have been recorded for seeds buried shallowly in loamy or sandy soil. 

Some Dalmatian toadflax seeds germinate in fall, but most germinate in spring. Seedlings 

(Figure 6b) grow quickly, and can establish a 20-inch (51 cm) long taproot within eight weeks 

of germination. Plants produce 2-5 erect flowering stems and prostrate non-flowering stems the 

first season (Figure 6a). The prostrate stems sprout in summer or early autumn and remain green 

throughout the winter, especially under snow cover. In the second year and subsequent years, there 

can be up to 25 flowering stems and up to 40 non-flowering stems arranged in a loose rosette at 

the base of the plant. Seasonal growth of stems can begin as early as February in warm areas, or as 

late as April in cooler, northern or high elevation areas. Flowering occurs throughout summer and 

fall (May to hard frost, depending on site conditions). Flowers are cross-pollinated by bumblebees 

and other large bees, and seeds are produced from summer to fall. A mature plant can annually 

produce up to 500,000 seeds that are gradually released through the fall and winter. Plants re-sprout 

each spring from adventitious buds on the root crown. Vegetative buds on lateral roots can produce 

new stems as early as three weeks after germination. Over time, these stems form new roots and 

eventually become independent plants. Severed root segments as short as 0.4 inches long (1 cm) can 

also develop into new plants. Dalmatian toadflax plants live 3-5 years on average. 

Habitat 

Soil disturbance is a very important contributor to Dalmatian toadflax seedling establishment. 

This weed is often found along railroads, riverbanks, and roadsides (Figure 9a), as well as in 

fallow fields, slash piles, abandoned lots, and overgrazed rangeland (Figure 9b). A variety of 

habitat types and plant communities can be invaded or become dominated by Dalmatian toadflax 

following heavy grazing, trampling, cultivation, logging, and burning. This weed thrives in cool, 

semiarid conditions and on coarse-textured soils. 

b

Figure 9. Dalmatian toadax infestations a. along a dirt road (Eric Coombs, Oregon Department of 

Agriculture); b. in a grazed pasture (Steve Dewey, Utah State University)(a,b bugwood.org) 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 2: Getting to Know Toadaxes 17 

Distribution 

Dalmatian toadflax is considered established in 31 states and ten Canadian provinces (Figure 

2b, repeated here in Figure 10a). It has been declared noxious in 14 of the states and three of 

the provinces in which it is currently established (Figure 10b)

a b

Figure 10. States and provinces where Dalmatian toadax is a. established (USDA PLANTS 

Database, EDDMapS); b. listed as noxious. 

Taxonomic Issues 

The taxonomy and distribution of Dalmatian toadflax have long been a point of contention, 

primarily due to large variations in leaf appearance. Dalmatian toadflax continues to be referred 

to by a range of scientific names, including Linaria genistifolia (L.) Mill., Linaria genistifolia 

(L.) Mill. ssp. dalmatica (L.) Maire & Petitm., and Linaria dalmatica (L.) Mill. (alone as well 

as with two subspecies). Two forms of Dalmatian toadflax are often mentioned (narrow-leaved 

and broad-leaved). These two forms may correspond 

to two subspecies (L. dalmatica ssp. macedonica 

and L. dalmatica ssp. dalmatica, respectively), or 

they may just represent variation in the leaves of 

one, all-encompassing Dalmatian toadflax species 

throughout its range. Dalmatian and yellow 

toadflax hybridizing in North America produce 

offspring that are intermediate in appearance of the 

two parental species, often with leaves more narrow 

than are typical for Dalmatian toadflax, but wider 

than typical for yellow toadflax. Drought-stressed 

Dalmatian toadflax plants frequently produce leaves 

that are narrower than typical, and drought stress 

later in the growing season can result in both broad 

and narrow leaves on the same plant (Figure 11). 

As of 2015, the taxonomic status of Dalmatian 

toadflax remains uncertain. The authors of this 

manual followed the taxonomic interpretation 

that Linaria genistifolia (L.) Mill., known by 

the common name of broomleaf toadflax, is very 

closely related to but distinct from L. dalmatica (L.) 

Figure 11. Dalmatian toadax recovering 

from drought-stress and grazing 

exhibiting dierent leaf forms on 

the same plant (Sarah M. Ward, 

Colorado State University) 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

18 Chapter 2: Getting to Know Toadaxes

Mill. Linaria genistifolia differs from Dalmatian toadflax primarily in the size of flowers and 

capsule fruit (Figure 12a-c); L. genistifolia flowers are significantly smaller (0.5-0.6 inches 

long or 12-16 mm) than the flowers of Dalmatian toadflax (0.8-1.6 inches long or 20-40 mm). 

The presence and distribution of L. genistifolia in North America remain unconfirmed at this 

time. The authors of this manual also followed the interpretation that L. dalmatica consists 

of two subspecies, of which only one (L. dalmatica ssp. dalmatica) is invasive and weedy in 

North America. DNA analysis may reveal that plants designated as one of the two subspecies 

of Dalmatian toadflax, or categorized as narrow- or broad-leaved forms of L. dalmatica, may 

in fact be hybrids of Dalmatian and yellow toadflax. The two forms may be unique species, 

whereby broad-leaved refers to L. dalmatica ssp. dalmatica and narrow-leaved refers to L. 

genistifolia. These uncertainties are currently being addressed. 

All of the control information presented in this manual for “Dalmatian toadflax” applies to wideleaved toadflax prevalent throughout North America, regardless of what species, subspecies, 

or form the ongoing genetic studies may reveal individual plants to be. When information is 

known to apply to confirmed Dalmatian and yellow toadflax hybrids, that information will be 

presented separately. 

a b c

Figure 12. Broomleaf toadax, Linaria genistifolia, growing in Europe a,b. wide-leaved form; c. narrowleaved form (a-c Ivo Toševski, CABI) 

Comments 

Toadflaxes produce secondary compounds known to deter herbivory, which may make them 

initially less attractive for grazing; however, with sufficient exposure, acceptance and even 

preference for grazing on Dalmatian toadflax typically increase. Cattle, sheep, and goats have 

been used to graze on and suppress Dalmatian toadflax. Grazing animals will pass viable 

Dalmatian toadflax seed in their excrement, so it is important to corral animals that have grazed 

on mature toadflax plants and feed them weed-seed free forage/hay to ensure the Dalmatian 

toadflax seed has been eliminated before moving them onto other pastures. This may take up 

to 72 hours. 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 2: Getting to Know Toadaxes 19 

Commonly Confused Species 

The combination of yellow, snapdragon-like flowers and large, waxy, heart-shaped or triangular 

leaves help differentiate Dalmatian toadflax from most potential look-alike species in North 

America. Myrtle spurge (Euphorbia myrsinites L.) is similar in appearance to Dalmatian 

toadflax (Figure 13a), except that myrtle spurge stems lean over instead of growing upright, 

they produce a milky sap when wounded, and they have typical spurge-type flowers that are 

green, inconspicuous, and surrounded by yellow-green bracts. Myrtle spurge is also listed as 

a noxious weed in several states. Goldenbanner species, including Thermopsis montana Nutt. 

and Thermopsis rhombifolia (Pursh) Richardson, have large, showy yellow flowers similar to 

Dalmatian toadflax, especially when viewed from afar (Figure 13b). Closer inspection reveals 

that goldenbanner leaves are always 3-parted and not succulent, and goldenbanner flowers 

do not have long spurs. The leaves, stems, and growth form of bastard toadflax (Comandra 

umbellata (L.) Nutt.) resemble those of Dalmatian toadflax; however, bastard toadflax leaves 

do not feel waxy to the touch, as they do for Dalmatian toadflax. Bastard toadflax also differs 

in its shorter overall height (maximum 1 foot or 30 cm), roots that are parasitic on other plants 

and also turn robin’s-egg blue when cut, and tiny whitish-pink flowers that appear only on the 

tip of the main stem (see Table 2 on page 26). 

Most other Linaria species present in North America (all of them exotic) have pink, purple, or 

bi-colored flowers. Linaria species present in North America that have yellow flowers are more 

likely to be confused with yellow toadflax and so are discussed on page 26. Yellow toadflax and 

yellow/Dalmatian toadflax hybrids are the plants most likely to be confused with Dalmatian 

toadflax. A section devoted to differentiating yellow, Dalmatian toadflax, and their hybrids can 

be found on page 34. 

a b

Figure 13. Potential Dalmatian toadax look-alikes a. myrtle spurge (Euphorbia myrsinites) (Jebulon); b. 

mountain goldenbanner (Thermopsis montana)(Steve Law) 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

20 Chapter 2: Getting to Know Toadaxes

Yellow Toadax 

Scientic Name 

Linaria vulgaris Mill. 

Common Names 

Yellow toadax, common toadax, butter-and-eggs, toad-ax, wild snapdragon, 

perennial snapdragon, axweed, ramsted, eggs and bacon, Jacob’s-ladder, common 

linaria, rabbit-ower, impudent lawyer 

Classication 

KINGDOM Plantae Plants 

SUBKINGDOM Tracheobionta Vascular plants

 SUPERDIVISION Spermatophyta Seed plants

 DIVISION Magnoliophyta Flowering plants

 CLASS Magnoliopsida Dicotyledons

 SUBCLASS Asteridae

 ORDER Lamiales

 FAMILY Plantaginaceae Plantain family

 GENUS Linaria Linaria

 SPECIES Linaria vulgaris Mill. Yellow toadflax 

History 

Yellow toadflax was introduced to North America from Eurasia by the late 1600s, likely as 

an ornamental plant, and for use in fabric dye and folk remedies. Yellow toadflax reportedly 

become naturalized in some eastern American colonies by 1671 and was considered a 

significant and fairly common agricultural weed as early as 1849. In Canada, yellow toadflax 

was first collected in the early 1800s in southern Quebec. The weed spread throughout the 

Prairie provinces, forming large populations in the early to mid-1900s. 

Description 

At a Glance 

Yellow toadflax (Figures 14, 18) is an erect, herbaceous perennial typically growing numerous 

stems 1-3 feet tall (0.3-1.0 m) from a taproot with spreading lateral roots. Leaves are alternate, 

green, pointed at both ends, and may have small petiole-like stalks. Older leaves are narrow and 

typically 1-2 inches long (2.5-5.0 cm) with a large central vein on the underside. Flowers are pale 

yellow and snapdragon-like with an obvious upper and lower lip and a spur pointing downward. 

Each has a fuzzy, bright orange throat. Flowers occur in spiked clusters at the top of the stem. 

Each flower produces an oval capsule fruit holding 10-40 viable, flat, disc-shaped seeds. 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 2: Getting to Know Toadaxes 21 

b

Roots 

Yellow toadflax develops taproots that 

can grow up to 3.3 feet deep (1 m). Roots 

have lateral branches that can extend 

several yards (meters) from the parent 

plant. Lateral roots have vegetative buds 

that produce new stems. Severed root 

segments as short as 4 inches long (10 

cm) can develop into new plants. 

Stems 

Plants typically grow 1-3 feet tall (0.3-

1.0 m), though stem height can vary 

dramatically, even for plants growing in 

the same vicinity (Figure 15a,b). Plants 

produce a few to hundreds of erect, 

leafy stems (Figure 14a). Most stems are 

woody and somewhat reddish at their 

base, becoming more slender, succulent, and greener toward the growing tip. Yellow toadflax 

stems die back completely in winter; unlike Dalmatian toadflax, yellow toadflax does not 

produce an overwintering rosette. 

Leaves 

Yellow toadflax leaves are alternate, pointed at both ends, and may be attached to the stem 

by small petiole-like stalks, though these are sometimes absent. Older leaves are narrow and 

typically 1-2 inches long (2.5-5.0 cm) with an obvious central vein on the underside. Leaves are 

green, often with a silvery tinge (Figure 16b). Though all yellow toadflax leaves are linear and 

have a consistent width along their length, the overall leaf width can vary significantly between 

infestations. Some leaves are quite slender and feathery (Figure 16a), some are moderately 

more robust but still pointed at the tip (Figure 16b), while others can be somewhat wider with 

rounded tips that give them the shape of a baseball bat (Figure 16c). Experienced observers 

may find that yellow toadflax leaves give off a distinctive “cat urine” odor. 

Figure 14. Yellow toadax plant (Linda Wilson, Ivo 

Toševski, CABI) 

a

Figure 15. Yellow toadax populations with a. short individuals; b. tall individuals (a, b Sharlene E. Sing, 

USDA FS RMRS) 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

22 Chapter 2: Getting to Know Toadaxes

a b c

Figure 16. Yellow toadax a. stems with feathery leaves; b. mid-width leaves (a, b Michael Shephard, 

Forest Service, bugwood.org); c. robust, rounded leaves (Sharlene E. Sing, USDA FS RMRS) 

Flowers 

Flowers are pale yellow and snapdragon-like with an obvious upper and lower lip and a spur 

pointing downward. The spur on yellow toadflax flowers is reduced compared to that on 

Dalmatian toadflax. Each flower is 0.8-1.6 inches long (2-4 cm) with a fuzzy, bright orange 

throat that functions as a nectar guide to entice pollinators (Figure 17a). Flowers occur in tightly 

grouped, spiked clusters at the tops of stems in groups of 6-30. Flowering occurs throughout 

the summer and into fall at some locations. 

Fruits and Seeds 

Each flower produces an oval-shaped capsule fruit (Figure 17b) that is 0.2-0.5 inches long 

(0.5-1.2 cm). Seed capsules have the potential to produce a maximum of 250 seeds, though 

most contain only 10-40 viable seeds. Seeds are very small, lightweight, flat, prominently 

winged discs, and approximately 0.06 inches in diameter (1.5 mm) (Figure 17c). A mature 

plant produces 1,500 to 30,000 seeds annually. 

a b c

Figure 17. Yellow toadax a. owers (Michael Shephard, Forest Service); b. fruits (John Cardina, Ohio 

State University); c. seeds (Steve Hurst, USDA NRCS PLANTS database) (a-c bugwood.org) 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 2: Getting to Know Toadaxes 23 

Figure 18. Line drawing of yellow toadax key traits of a. plant; b. ower; c. fruit; d. seed 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

24 Chapter 2: Getting to Know Toadaxes

Biology and Ecology 

Yellow toadflax spreads by seeds, creeping roots, and root fragments. Seeds are dispersed 

from late summer through winter, and typically spread by humans and animals. Seeds can be 

caught on motorized equipment, mud on tires or clothing, hay, or animal fur. Because seeds 

ingested by animals often remain viable upon defecation, livestock, birds, elk, and deer grazing 

toadflax fruits in autumn is one of the primary modes of toadflax long distance seed dispersal. 

Yellow toadflax seeds have low viability, with germination rates commonly less than 50%. 

Some researchers have reported that seed capsules maturing late in the season (November) 

contained more viable seeds than those maturing earlier in the season (September), though 

this may not be true for all yellow toadflax populations. While some yellow toadflax seeds 

germinate immediately, many can remain dormant but viable in the soil for 8 years or more. 

Yellow toadflax seeds germinate in spring. Seedlings grow quickly, developing lateral roots 

capable of vegetative reproduction within three weeks of germination. Plants can produce up 

to 100 stems from the root system during the first growing season, then up to 250 new shoots 

during the second year. Because all yellow toadflax stems die back completely in winter, spring 

re-growth in established plants occurs only from sub-soil root buds (Figure 19a) and not, as is 

the case for Dalmatian toadflax, from an overwintered rosette. Spring stem growth (Figure 19b) 

begins as early as March in warm regions, or in April or even later in cooler, more northerly 

or high elevation sites. Flowering occurs throughout summer and into fall (May to November, 

depending on site conditions). Flowers are cross-pollinated by bumblebees and other large 

bees, and seeds are produced from summer to fall. A mature plant can produce 1,500 to 30,000 

seeds annually, on average. These are gradually released from the seed capsules throughout 

fall and winter. Plants re-sprout each spring from adventitious buds in their roots. Severed root 

segments as short as 4 inches long (10 cm) can also develop into new plants. Yellow toadflax 

plants live four years on average. 

a b

Figure 19. Yellow toadax a. overwintering subsoil root buds (inside yellow circle); b. 

stems sprouting in spring (a, b Sharlene E. Sing, USDA FS RMRS) 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 2: Getting to Know Toadaxes 25 

Habitat 

Soil disturbance can be an important contributor to yellow toadflax seedling establishment. 

The weed is often found at chronically disturbed sites such as roadsides, railroads, cultivated 

fields, pastures, and rangeland. Yellow toadflax has also been found in backcountry locations 

where there has been very little to no disturbance, indicating it also has the ability to invade 

healthy ecosystems. Yellow toadflax is a common weed across North America occurring in a 

variety of habitat types and plant communities (Figure 18a-c). It is frequently found in more 

fertile and moist soil than Dalmatian toadflax. 

a b c

Figure 20. Yellow toadax infestations a. plants in a roll of barbed wire; b. in a montane forest 

opening (a, b Hal Pearce, USDA FS); c. in a eld in the sagebrush steppe (Mark 

Schwarzländer, University of Idaho, bugwood.org) 

Distribution 

As of 2015, yellow toadflax is considered established in all 49 continental states, ten Canadian 

provinces and two Canadian territories (Figure 2a, repeated here in Figure 21a). It has been 

declared noxious in 13 of the states and three of the provinces where it is currently established 

(Figure 21b). Yellow toadflax is more likely to be a minor contributor to plant communities 

composed of mixed weedy and native species in the eastern USA and Canada, but is capable of 

generating significant monoculture infestations in the Intermountain West. 

a b

Figure 21. States and provinces where yellow toadax is a. established (USDA PLANTS Database, 

EDDMapS); b. listed as noxious 
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26 Chapter 2: Getting to Know Toadaxes

Comments 

Toadflaxes produce secondary compounds known to deter herbivory, which may make them 

initially less attractive for grazing; however, with sufficient exposure, acceptance and even 

preference for grazing on yellow toadflax typically increase. Both cattle and sheep have been 

trained to feed on yellow toadflax. Grazing animals can pass viable yellow toadflax seed in their 

excrement, so it is important to corral animals that have grazed on mature toadflax plants, and 

feed them weed-seed free forage/hay to ensure the yellow toadflax seed has been eliminated 

before moving them onto other pastures. This may take up to 72 hours. 

In states where yellow toadflax is not listed as noxious, it still is sold by some nurseries as 

“butter and eggs,” “Jacob’s ladder,” or “wild snapdragons,” and is frequently included in seed 

mixes sold for wildflower and pollinator gardens. 

Commonly Confused Species 

The large, yellow snapdragon-like flowers help differentiate yellow toadflax from most potential 

look-alikes. The majority of Linaria species present in North America (all of them exotic) have 

pink, purple, or bi-colored flowers. There are two Linaria species present in North America 

and one cultivated yellow snapdragon (Antirrhinum majus L.) with similar yellow flowers that 

could be confused with yellow toadflax. Other species present in North America have foliage 

and growth traits similar to yellow toadflax, and could be confused for this species, especially 

when observed prior to flowering. Some of the species that most closely resemble yellow 

toadflax are listed in Table 2, along with key characteristics that can be used to differentiate the 

look-alikes. 

Dalmatian toadflax and yellow/Dalmatian toadflax hybrids are the plants most likely to be 

confused with yellow toadflax. A section devoted to differentiating yellow, Dalmatian toadflax, 

and their hybrids can be found in Table 3 on page 34. 

Table 2. North American species similar in appearance to yellow toadax, and key traits for 

dierentiation. 

SPECIES IMAGE DIFFERENTIATING FEATURES 

Ballast toadflax 

Linaria spartea 

Plantain Family 

Exotic annual forb 

Weed 

Ballast toadflax, an exotic Linaria reportedly 

present only in Connecticut and Michigan, is 

weedy along roadsides, fields and waste areas. 

Similarities to yellow toadflax: snapdragonlike flowers; narrow leaves. Differences from 

yellow toadflax: lacks lateral roots; tiny but 

obvious hairs present on upper stems; leaves are 

narrower (less than 1 mm wide). 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 2: Getting to Know Toadaxes 27 

SPECIES IMAGE DIFFERENTIATING FEATURES 

Bastard toadflax Bastard toadflax grows on open wooded hillsides, 

Comandra umbellata rocky outcrops, and in upland rangeland. 

Sandalwood Family Similarities to yellow toadflax: habitats occupied; 

Native perennial forb leaf and growth form; stems have a reddishor subshrub colored base. Differences from yellow toadflax: 

shorter height (maximum 1 foot or 30 cm); 

presence of rhizomes; parasitic roots; rhizomes 

turn robin’s-egg blue when cut; leaves drier to the 

touch with obvious lateral veins on the underside; 

tiny, whitish-pink, five-petal flowers that only 

appear at the tip of the stem. 

Leafy spurge Leafy spurge, also frequently listed as a noxious 

Euphorbia esula weed, inhabits many of the same habitats as 

Spurge Family yellow toadflax. Similarities to yellow toadflax: 

Exotic perennial forb creeping lateral roots; linear leaves; growth 

Weedy; listed as form. Differences from yellow toadflax: 

noxious in many states milky sap produced by foliage and stem 

when damaged; inconspicuous green flowers 

surrounded by yellow-green bracts. 

Leafy spurge Prostrate toadflax is a rare, exotic Linaria 

Euphorbia esula ornamental that could escape into disturbed, 

Spurge Family waste areas, similar to yellow toadflax. 

Exotic perennial forb Other similarities to yellow toadflax: yellow 

Weedy; listed as snapdragon-like flowers; long, narrow leaves. 

noxious in many states Differences from yellow toadflax: does not 

have lateral roots; upper stems have tiny hairs; 

leaves are narrower; stems are more sprawling; 

maximum plant height is 8 inches (20 cm). 

Stoneseed Stoneseed grows in similar habitats to yellow 

Lithospermum toadflax in western North America, including 

ruderale rangeland, forest openings, moist roadsides, 

Forget-me-not Family and abandoned fields. Similarities to yellow 

Native perennial forb toadflax: height; produces numerous stems; 

leaf shape and form of leaf attachment to stem. 

Differences from yellow toadflax: does not 

have lateral roots; leaves and stems are covered 

with fine hairs; has small, star-shaped flowers 

with 5 whitish-yellow petals. 

Yellow snapdragon Yellow snapdragon is often planted as an 

Antirrhinum majus ornamental; it could co-occur with yellow 

Plantain Family toadflax where it has escaped cultivation or 

Exotic annual to where yellow toadflax invades gardens and 

perennial forb fields. Similarities to yellow toadflax: color and 

Used as an ornamental form of flowers; alternate, long, and narrow 

leaves. Differences from yellow toadflax: 

flowers and leaves are larger; has multiple 

leaves per axil; roots are typically fine and not 

creeping. 

Ballast toadax (Javier Martin); Bastard toadax (©2015 Keir Morse); Leafy spruge (K. George Beck & 

James Sebastian, Colorado State University, bugwood.org); Prostrate toadax (Ghislain 

118 (AD); Stoneseed (Matt Lavin, Bozeman MT); Yellow snapdragon (MChance666) 
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28 Chapter 2: Getting to Know Toadaxes

Hybrid Toadax 

Scientic Name 

Linaria vulgaris x L. dalmatica; Linaria dalmatica x L. vulgaris 

Common Names 

Hybrid toadax 

Classication 

KINGDOM Plantae Plants

 SUBKINGDOM Tracheobionta Vascular plants

 SUPERDIVISION Spermatophyta Seed plants

 DIVISION Magnoliophyta Flowering plants

 CLASS Magnoliopsida Dicotyledons

 SUBCLASS Asteridae

 ORDER Lamiales

 FAMILY Plantaginaceae Plantain family

 GENUS Linaria Linaria

 SPECIES Linaria vulgaris x L. dalmatica Hybrid toadflax 

History 

By the late 1800s, yellow and Dalmatian toadflax were introduced to North America from 

Eurasia and southeastern Europe, respectively, for ornamental and medicinal purposes. Hybrids 

of these species were first reported in North America in 2009. 

Description 

Due to the many possible combinations of genetic contributions of either parental toadflax 

species, a set description for hybrid toadflax is impossible. Hybrids may very closely resemble 

Dalmatian toadflax if the genetic contribution from yellow toadflax was only minor, or vice 

versa. In the most clear-cut cases, hybrid toadflax presents traits that are truly intermediate 

between both parent species (Figure 22). The below descriptions are based on a combination 

of traits exhibited by both parental toadflax species and are supplemented by field observations. 

Hybrid toadflaxes are erect, herbaceous perennials that grow few to numerous stems 1-3 feet 

tall (0.3-1.2 m), although individual hybrids may grow shorter or taller depending on site 

conditions and the interaction of genes. Dalmatian toadflax has a prominent taproot with short 

lateral roots, while yellow toadflax has a comparatively smaller taproot and more developed 

lateral roots. Hybrids observed in the field have possessed prominent taproots as well as 

prominent lateral roots. 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 2: Getting to Know Toadaxes 29 Figure 22. Toadax plants a. Dalmatian toadax; b,c. hybrid toadax; d. yellow toadax (a-d Sharlene E. Sing, USDA FS RMRS) 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

30 Chapter 2: Getting to Know Toadaxes

Dalmatian toadflax leaves are often heart-shaped, waxy, thick, clasp the stem, and have multiple 

veins (Figure 22a) while yellow toadflax leaves are often long and narrow, non-waxy and 

thin, and have short stalks and a single prominent midvein (Figure 22d). The leaves on hybrid 

toadflax are highly variable in terms of size, shape, and color (Figure 22b,c; Figure 23a-c). 

Hybrid leaves are generally wider than yellow toadflax leaves, usually do not clasp the stem, 

have a prominent midvein as well as multiple, less prominent side veins, and are intermediate 

in terms of thickness and waxy texture. Because both Dalmatian and yellow toadflax leaves 

can vary considerably depending on local population genetics and site conditions (Figure 

22a,d), intermediate leaf forms are not always a reliable characteristic for identifying hybrid 

individuals. 

Figure 23. Variation in hybrid toadax leaves (a-c Sarah M. Ward, Colorado State University) 

Hybrid toadflax blossoms can range in color from the pale yellow of yellow toadflax to the 

bright yellow of Dalmatian toadflax (Figure 24 a-c). Hybrids have an orange throat, though this 

can sometimes resemble either the vibrant orange throat of yellow toadflax or the less bright 

coloration of Dalmatian toadflax. Similar to both parent species, hybrid toadflax flowers have 

a snapdragon-like shape with two lips and a long spur. Hybrid toadflax flowers occur in spiked 

clusters either at the top of the stem or from leaf axils from summer through fall. Fruit capsules 

of hybrid toadflax are similar in size and shape to both Dalmatian and yellow toadflax (round 

and 0.2-0.5 inches or 0.5-1.2 cm long). Hybrid seeds are variable in shape; they can resemble 

those of Dalmatian or yellow toadflax, or be intermediate in form (Figure 25). 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 2: Getting to Know Toadaxes 31 

a b c d e

Figure 24. Variation in hybrid toadax owers (a-d Sarah M. Ward, Colorado State University; e Sharlene 

E. Sing, USDA FS RMRS) 

Figure 25. Toadax seeds: yellow toadax (left), hybrid toadax (center), Dalmatian toadax (right) (Sarah 

M. Ward, Colorado State University) 

Biology and Ecology 

Similar to both parent species, hybrid toadflax spreads by seeds, lateral roots, and root fragments. 

Toadflax hybrid seeds are highly viable, dispersed from late summer through winter, and are 

likely spread by humans and animals. Seeds can likely be caught on motorized equipment, 

mud on tires or clothing, hay, or animal fur. As far as we know, hybrid toadflax seeds ingested 

by animals may remain viable upon defecation, and so ingestion by livestock, birds, elk, and 

deer grazing toadflax fruits in autumn may contribute to long distance seed dispersal. Hybrid 

toadflax grown under controlled conditions produces large quantities of viable seeds. Seed 

production by hybrids growing under typical field conditions and across the full range of 

known hybrid-infested sites requires additional investigation. 

Seasonal growth of stems has been observed as beginning earlier in the spring for hybrid 

toadflax compared to either parent species. Flowering occurs throughout summer and into 

fall, depending on site conditions. Similar to both parent species, hybrid flowers are cross-
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

32 Chapter 2: Getting to Know Toadaxes

pollinated by bumblebees and other large bees, and seeds are produced from summer to fall. It 

is not yet known how long hybrid toadflax plants live on average, though neither parent species 

typically lives longer than five years. 

Habitat 

Soil disturbance is a very important contributor to Dalmatian and yellow toadflax seedling 

establishment. Hybrid toadflaxes have been found in chronically disturbed sites suitable for 

either parent species, including roadsides, riverbanks, slash piles, abandoned lots, pastures, 

and rangeland in a variety of soils and climatic conditions (Figure 26a-b). The presence of both 

Dalmatian and yellow toadflax on-site increases the possibility that hybridization has taken 

place, although on some sites, either or both parental species may have been eliminated by 

competitively superior hybrid offspring. 

a b

Figure 26. Hybrid toadax infestations a. in a forest understory, with Dalmatian toadax uphill, hybrid 

 toadax plants mid-slope, and yellow toadax downhill; b. following a prescribed burn for

 aspen regeneration (a,b Sharlene E. Sing, USDA FS RMRS) 

Distribution 

As of 2015, hybrid toadflaxes were confirmed as present in five western states (Figure 2c, 

repeated here in Figure 27a). Scouting continues to be the best way to identify other potential 

hybrid toadflax populations in North America. Due to the recent confirmation of naturally 

occurring infestations, hybrid toadflax has thus far only been listed as noxious in Colorado. 

However, the other states and provinces where the parent species are declared noxious (Figures 

10b and 17b, repeated here in Figures 27b and 27c, respectively) may likely also treat hybrid 

toadflax as noxious. 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 2: Getting to Know Toadaxes 33 

a b c

Figure 27. States and provinces where a. hybrid toadax is established (Sarah M. Ward, unpublished 

data); b. Dalmatian toadax is listed as noxious; c. yellow toadax is listed as noxious 

Comments 

Grazing animals can pass viable yellow and Dalmatian toadflax seed in their excrement. 

Though not yet studied, this is likely also true for hybrid toadflax. It is important to corral 

animals that have grazed on mature toadflax plants, and feed them weed-seed free forage/hay 

to ensure the toadflax seed has been eliminated before moving them onto other pastures. This 

may take up to 72 hours. 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

34 Chapter 2: Getting to Know Toadaxes

Table 3. Comparison of Dalmatian toadax, yellow toadax, and their hybrids.

Feature Dalmatian toadflax Yellow toadflax Hybrid toadflax

LEAVESDalmatian: waxy, heart-shaped, significant outward bulging mid-leaf, clasping, multiple prominent veinsYellow: not waxy, linear (consistent width entire length), short stalk (non-clasping), single prominentvein, ‘aromatic’Hybrid: often one prominent midvein with many lessprominent side veins, many intermediate combinationsof both parents, mid-leaf outward bulging typically lessexaggerated than in Dalmatian toadflaxFLOWERSDalmatian: bright yellow, yellowish-orange throat, long spurYellow: pale yellow, bright orange throat, spur and blossom slightly shorter than Dalmatian toadflax, tightclustering of flowers resembles small popcorn ballsHybrid: often medium orange throat, many intermediate combinations of both parentsSEEDSDalmatian: triangular Yellow: winged, roundedHybrid: moderately winged triangular

Dalmatian, yellow, and hybrid toadax leaves (Sharlene E. Sing, USDA FS RMRS); Dalmatian toadax owers (Bonnie Million, National Park Service, bugwood.

org), yellow toadax owers (Mary Ellen Harte, bugwood.org); Dalmatian and yellow toadax seeds (Steve Hurst, USDA NRCS PLANTS database); Hybrid toadax owers, seeds (Sarah M. Ward, Colorado State University) 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 3: Biology of Toadax Biocontrol Agents

CHAPTER 3: BIOLOGY OF TOADFLAX BIOCONTROL AGENTS 

Basic Insect Biology 

Insects are the largest and most diverse class of animals. Basic knowledge of insect anatomy 

and lifecycle will help in understanding insects, and recognizing them in the field. 

Most insects used in weed biocontrol have complete metamorphosis, which means they exhibit 

a life cycle with four distinct stages: egg, larva, pupa, and adult (Figure 28). Insects have an 

exoskeleton (a hard external skeleton) and a segmented body divided into three regions (head, 

thorax, and abdomen, Figure 29a,b). Adult insects have three pairs of segmented legs attached 

to the thorax, and a head with one pair each of compound eyes and antennae. 

Figure 28. Line drawings of a beetle lifecycle showing complete metamorphosis (University of Idaho) 

Head

Head

Abdomen

Figure 29. Line drawings of insect anatomy a. beetle; b. moth (a,b adapted from Biological Control of 

Weeds in the West, Rees et al. 1996) 

Thorax

Abdomen

↑

Thorax

35 
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36 Chapter 3: Biology of Toadax Biocontrol Agents

Because insects have an external skeleton, they must shed their skeleton in order to grow. This 

process of shedding the exoskeleton is called molting. Larval stages between molts are called 

“instars.” Larvae generally complete three to five instars before they molt into pupae. During 

the pupal stage, insects change from larvae to adults. Insects do not feed or molt during the pupal 

stage. Adult insects emerge from the pupal stage and do not grow or molt. 

Toadax Biological Control Agents 

Nine species of exotic insects have been intentionally or accidentally introduced for biocontrol of 

toadflax in North America. They belong to two groups: beetles and moths. 

Beetles (Order Coleoptera) 

Adult beetles are hard-bodied insects with tough exoskeletons. Adult beetles possess two pairs 

of wings. The two front wings, called elytra, are thickened and meet in a straight line down the 

abdomen, forming a hard, shell-like, protective covering (Figure 29a). The two hind wings are 

membranous and used for flight. These are larger and are folded under the elytra when not in use. 

Beetle larvae are grub- or worm-like with three small pairs of legs, allowing some to be quite 

mobile. Many are pale white with a brown or black head capsule, though some may be quite 

colorful and change markedly in appearance as they grow. Beetles, like those used for toadflax 

biocontrol, have chewing mouthparts. 

Species from two different families are used for toadflax biocontrol: weevils (Curculionidae) and 

flower beetles (Kateretidae). Weevils are plant-feeding beetles with chewing mouthparts at the 

tip of a long snout. They use their snouts to chew inside plant tissues to feed or to notch out holes 

in which they lay their eggs. Some adult weevils cause significant foliar feeding damage. Weevil 

larvae feed internally in the flowers, seeds, stems, or roots of their target plants. Weevil larvae 

often cause more damage to plants than adult weevils. 

Adult flower beetles are small, dark, oval insects that eat leaves, young stems, and occasionally 

floral tissues and pollen. Flower beetle larvae live inside the flower and consume floral tissue, 

pollen, and developing seeds. Both larval and adult flower beetles can cause significant feeding 

damage to their host plants. 

Butteries and Moths (Order Lepidoptera) 

Adult moths are soft-bodied insects with two pair of membranous wings that are covered with 

powder-like scales (Figure 29b). Adult moths have prominent antennae and coiled mouthparts 

that are adapted to siphoning sap and nectar from plant flowers. They can be bright- or dullcolored, and males and females of the same species do not always have the same coloration. 

Adult moths feed very little, if at all, and do not damage their host plant. Moth larvae (known 

as caterpillars) have a toughened head capsule, chewing mouthparts, and a soft body. They are 

active feeders, developing internally or externally on the host plant. The pupal stage of moths 

is known as a chrysalis and is often enclosed in a cocoon. The moth species used for toadflax 

biocontrol in North America belong to two families: the Noctuidae and the Cosmopterigidae. 

Insects used for North American toadflax biocontrol attack different parts of the plant. They 

include two seed-feeding weevils, a flower-feeding beetle, two stem-mining weevils, a root-
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Chapter 3: Biology of Toadax Biocontrol Agents

galling weevil, a defoliating moth, and two root-boring moths. As such, roots, stems, flowers, 

seeds, and foliage are all attacked by the toadflax biocontrol agents. Toadflax biocontrol agents 

preferentially attack Dalmatian or yellow toadflax, but may survive to some degree on both 

species and potentially on their hybrids. Figure 28 illustrates the toadflax species and plant parts 

attacked by each biocontrol agent. Each insect is described in detail in the following sections, 

with separation between beetles and moths. All toadflax biocontrol agents already established in 

North America are summarized and compared in Tables 4-6 near the end of this chapter. 

Seed feeders 

Rhinusa antirrhini 

Rhinusa neta 

Flower feeder 

Brachypterolus 

pulicarius 

Stem miners 

Mecinus janthinus 

M. janthiniformis 

Defoliator 

Calophasia lunula 

Root borers 

Eteobalea intermediella 

E. serratella 

Root galler 

Rhinusa linariae 

Figure 30. Generalized drawing of toadax, including the biocontrol agents and the plant parts they attack. Note: 

Most biocontrol agents can attack both Dalmatian and yellow toadax but have a preference for one 

of the two species. Rhinusa spp., Brachypterolus pulicarius, Eteobalea serratella, and Mecinus janthinus 

prefer yellow toadax; E. intermediella and M. janthiniformis prefer Dalmatian toadax. All biocontrol 

agents listed above are able to attack hybrid toadax. (Plant: modied from Regina O. Hughes, mtwow. 

org); R. antirrhini (Ivo Toševski, CABI); R. neta (Gyorgy Csoka, Hungary Forest Research Institute); B. 

pulicarius (Daniel K. MacKinnon, Colorado State University); R. linariae, Mecinus spp. (Bob Richard, USDA 

APHIS PPQ); C. lunula (Laura Parsons, University of Idaho); E. intermediella (Ivo Toševski, CABI) 

37 
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38 Chapter 3: Biology of Toadax Biocontrol Agents

Brachypterolus pulicarius (L.) 

Toadax ower-feeding beetle 

Order Coleoptera 

Family Kateretidae 

Native distributiON Europe 

OrigiNal sOurce USA: Accidental 

CAN: Accidental 

First release USA: 1919 

CAN: 1953 

NONtarget eFFects None reported 

Description 

Eggs appear milky white at first, becoming yellow just before hatching. Larvae are yellow and 

up to 7 mm long. The larval head capsule starts out dark brown to black and wider than the 

abdomen, but by the third instar, lightens to a golden brown and becomes more slender than the 

body (Figure 31a). Pupae are up to 3 mm long and 2 mm wide. Adults are shiny, dark brown 

to black, or sometimes black with brown mottling. They are 2-3 mm long and somewhat ovalshaped (Figure 31b). 

a b c

Figure 31. Brachypterolus pulicarius a. larva; b. adult (a,b Daniel K. MacKinnon, Colorado State University); 

c. adults on toadax owers and buds (Susan Turner, British Columbia Ministry of Forests) (a-c 

bugwood.org) 

Life Cycle 

Adults emerge in late spring and feed on young toadflax shoot tips and leaf buds. Females lay 

eggs singly into unopened toadflax buds, just beneath the folded petals. Larvae feed on flower 

pollen, anthers, ovaries, and immature seeds. They develop through three instars and drop to 

the soil in fall to overwinter as pupae in soil or plant litter. There is one generation per year. 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 3: Biology of Toadax Biocontrol Agents 39 

Egg 

Larva 

Pupa 

Adult 

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 

Figure 32. Schematic life cycle of Brachypterolus pulicarius. Bars indicate the approximate length of 

activity for each life stage; dates will vary depending on local conditions. Black bars represent 

the inactive overwintering period. 

Habitat Preference 

The toadflax flower-feeding beetle is well adapted to a variety of environmental conditions and 

can be found throughout the majority of toadflax infestations in North America. 

Damage 

Adult feeding can delay flowering and reduce the number of healthy flowers (and thereby 

seeds) produced by yellow toadflax. At high densities, adult feeding increases branching and 

reduces the height of Dalmatian toadflax plants. Injury from larval feeding is generally more 

significant, reducing seed output by more than 75% in attacked flowers. Seeds surviving to 

maturity in attacked flowers are smaller, lighter weight, and less viable. Decreasing seed output 

does not kill existing plants but can help reduce the rate of spread and genetic diversity of 

toadflax populations. 

Current Status and Availability 

This beetle was unintentionally introduced. First reported on yellow toadflax in New York, 

it has spread naturally and via redistributions throughout North America on both yellow and 

Dalmatian toadflax. Brachypterolus pulicarius biotypes (or strains) were believed to have 

evolved to specialize on either yellow toadflax or Dalmatian toadflax; however, a recent study 

found no genetic basis for this claim. B. pulicarius prefers and performs better on yellow 

toadflax, even for individuals collected from Dalmatian toadflax. Its use of Dalmatian toadflax, 

therefore, remains incidental in both the USA and Canada. 

On Dalmatian toadflax in the USA, high densities (such as those observed in Idaho, Oregon, 

and Washington) can stunt stem height and cause increased branching. However, the overall 

impact on Dalmatian toadflax flowering and seed production is considered minimal at most 

sites. Brachypterolus pulicarius is typically more abundant on yellow toadflax in the USA, 

delaying flowering and reducing seed production by 80-90% at some locations. However, the 

overall impact on yellow toadflax populations also appears to be minimal. 

On yellow toadflax in Canada, B. pulicarius is abundant, but its overall impact has been limited. 

It delays flowering and seed production, but has not truly changed the scope or prevalence of 

problems associated with yellow toadflax. B. pulicarius is found sporadically on Dalmatian 

toadflax in Canada but appears to be too rare to have any major impact on seed production. The 

impacts of B. pulicarius on hybrid toadflax have not yet been studied in North America. 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

40 Chapter 3: Biology of Toadax Biocontrol Agents

a b

Figure 33. North American establishment of Brachypterolus pulicarius on a. Dalmatian 

toadax; b. yellow toadax. Note: B. pulicarius is anecdotally reported as established 

on yellow toadax in other northeastern states in the USA not specied in the 

literature. 

Comments 

Though B. pulicarius was first an accidental introduction in the USA, it is approved for 

redistribution within North America. Because the beetle is already widespread and its overall 

impact is low, it is not a high priority for redistribution. 

Adult B. pulicarius can be differentiated from the other toadflax beetle species by their lack 

of snouts; the other toadflax beetles are weevils and have long snouts. Competition between 

Rhinusa antirrhini and Brachypterolus pulicarius prevents both species from having an additive 

impact in many locations. 

Adult B. pulicarius have been observed feeding on the pollen of many plant species, including 

dandelion, clovers, wild mustards, strawberry, apple, and dogwood. This feeding causes little 

to no impact. 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 3: Biology of Toadax Biocontrol Agents 41 

Mecinus janthinus Germar 

Yellow toadax stem-mining weevil 

Mecinus janthiniformis Toševski & Caldara 

Dalmatian toadax stem-mining weevil 

Mecinus janthinus 

Order Coleoptera 

Family Curculionidae 

Native distributiON Eurasia 

OrigiNal sOurce USA: France, Germany 

CAN: France, Germany 

First release 

USA: 1996 

CAN: 1991 

NONtarget eFFects None reported 

Mecinus janthiniformis 

Order Coleoptera 

Family Curculionidae 

Native distributiON southeastern Europe 

OrigiNal sOurce 

USA: Macedonia via Canada 

CAN: Macedonia 

First release USA: post 1996 

CAN: 1992 

NONtarget eFFects None reported 

Description 

These species are morphologically very similar. Eggs are white and oval-shaped. Larvae are 

C-shaped, creamy-white with brown head capsules, and are up to 5 mm long (Figure 34a). 

Adults are bluish-black (rarely greenish-black), elongated, and have long snouts (Figure 34c). 

Newly emerged adults may have a subtle metallic sheen that becomes more dull black with 

age. Mecinus janthinus adults are smaller (2.4-3.4 mm vs. 3.2-6.0 mm long, excluding snout) 

and their snouts are less abruptly curved than M. janthiniformis. Otherwise, these two species 

are nearly identical. 
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42 Chapter 3: Biology of Toadax Biocontrol Agents

a b c

Figure 34. Mecinus spp. a. larva (Rosemarie De Clerck-Floate, Agriculture and Agri-Food 

Canada); b. pupa; c. adult. Top bar M. janthinus, bottom bar M. janthiniformis (b,c 

Bob Richard, USDA APHIS PPQ) (a-c bugwood.org) 

Life Cycle 

Overwintering adults emerge in early spring and feed on shoot tips. In the native range, Mecinus 

janthinus reportedly emerges a few weeks earlier on yellow toadflax than M. janthiniformis 

does on Dalmatian toadflax (Figure 35,36). Spring emergence of adult weevils in North 

America varies significantly due to the influence of site-specific characteristics such as latitude, 

elevation, aspect, and residual snow cover. Adult feeding on toadflax shoot tips and leaves 

produces a distinctive shot hole injury pattern, which tends to be more obvious on Dalmatian 

toadflax. Females chew holes into toadflax stems and lay eggs singly (up to 45 in a lifetime), 

covering eggs with chewed plant tissue. Larvae feed through three instars in short tunnels 

chewed inside the toadflax stems. Mecinus janthinus tends to mine lower in toadflax stems than 

M. janthiniformis. Pupation occurs in mid-summer in chambers located in the larval feeding 

tunnels. Development to adulthood occurs by late summer, with adults overwintering inside the 

pupal chambers. There is one generation per year, with all development from egg deposition to 

adult emergence the following spring taking place in the same toadflax stem. 

Egg 

Larva 

Pupa 

Adult 

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 

Figure 35. Schematic life cycle of Mecinus janthinus. Bars indicate the approximate length of activity 

for each life stage; dates will vary depending on local conditions. Black bars represent the 

inactive overwintering period. 

Egg 

Larva 

Pupa 

Adult 

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 

Figure 36. Schematic life cycle of Mecinus janthiniformis. Bars indicate the approximate length of activity 

for each life stage; dates will vary depending on local conditions. Black bars represent the 

inactive overwintering period. 
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Chapter 3: Biology of Toadax Biocontrol Agents 43 

a

Habitat Preference 

Mecinus janthiniformis is well adapted to a variety of environmental conditions and can be 

found on many Dalmatian toadflax infestations in North America. The overwintering of adults 

within dead Dalmatian toadflax stems, which typically stand above snow cover, exposes the 

weevils to extremes in fluctuating ambient temperature and humidity. Adult mortality can 

reach 75 to 100% where temperatures drop lower than -18.5° F (-28° C); however, affected 

populations can rebound over time. Mecinus janthinus prefers milder, low-elevation sites in 

its native range compared to M. janthiniformis. The North American distribution and habitat 

preferences of M. janthinus are still being determined; however, successful yellow toadflax 

biological control with M. janthinus has been observed at elevations above 7,000 feet (2,180 

m), and establishment so far has been confirmed at latitudes of up to 53.5° N in Northern 

Alberta, Canada. 

Damage 

Adult weevils consume/chew on the growing tips of toadflax shoots, stems, and leaves, producing 

a distinctive shot hole injury pattern (Figure 37a, 38a). This damage weakens the plant, can 

suppress flowering and seed production, and severely stunts shoots. Large aggregations of M. 

janthiniformis adults feeding on new toadflax shoot growth can result in significant injury to 

shoot tips and leaves; heavily attacked shoot tips may turn brown and shrivel. Larval mining 

(Figure 37c) severs water/nutrient-conducting tissues, causing desiccation and death (Figure 

38b). Larval feeding also likely depletes nutrient reserves in the roots, which is important for 

the year-to-year persistence of individual plants. Repeated, yearly attack by both adults and 

larvae can lead to striking reductions in toadflax plant density. 

a b c

Figure 37. Mecinus spp. damage on Dalmatian toadax a. adult feeding on leaves; b. oviposition scars 

(a,b Sharlene E. Sing USDA FS RMRS); c. larval mining (Laura Parsons, University of Idaho) 

b

Figure 38. Mecinus spp. damage on yellow toadax a. adult and feeding holes on foliage; b. 

plants dying from larval mining (a,b Sharlene E. Sing USDA FS RMRS) 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

44 Chapter 3: Biology of Toadax Biocontrol Agents

Current Status and Availability 

Agents originally released in the USAand Canada as Mecinus janthinus were recently discovered 

to be a mixture of M. janthinus and a closely related species, M. janthiniformis. Field surveys 

and lab-based experiments have determined that M. janthiniformis prefers Dalmatian toadflax. 

Mecinus janthiniformis is currently established in northwestern North America (Figure 39a), 

where it has reduced Dalmatian toadflax populations dramatically at some locations. 

Surveys and studies have similarly found that M. janthinus prefers yellow toadflax. While 

currently not widely distributed (Figure 39b), M. janthinus densities and impact on yellow 

toadflax can be high locally, and this species appears to establish well in new areas. The impacts 

of Mecinus spp. on hybrid toadflax have not yet been fully determined. 

a b

Figure 39. North American establishment of a. Mecinus janthiniformis on Dalmatian toadax; b. Mecinus 

janthinus on yellow toadax; Note: because the identication of M. janthiniformis has only 

recently been made, sorting the establishment status of each Mecinus species on the two 

toadax species is a work in progress in North America. 

Comments 

Mecinus spp. weevils are strong fliers and can easily disperse throughout toadflax-infested 

areas. Field observations showed that in southern British Columbia, M. janthiniformis was 

capable of spreading over 2 miles (3.2 km) in four years. Mecinus janthinus readily located 

isolated plants and small toadflax populations throughout an extensive area where it had become 

established in west-central Montana. Dalmatian toadflax has live prostrate stems that persist 

even under snow over winter, providing a food supply and little incentive for newly emerged 

adult M. janthiniformis to disperse in spring. Because there is no equivalent overwintering 

rosette produced by yellow toadflax, adult M. janthinus emerging in spring are left marooned 

without a food supply and readily disperse to seek out host plants. 

Low rates of parasitism have been documented on Mecinus spp. in the USA and Canada. Adult 

Mecinus spp. can be differentiated from the other toadflax weevil species by their elongated 

shape, compared to the more rounded bodies of Rhinusa spp. Adult Brachypterolus pulicarius 

do not have the snouts of the Mecinus and Rhinusa weevils. 
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Chapter 3: Biology of Toadax Biocontrol Agents 45 

Rhinusa antirrhini (Paykull) 

Toadax seed-galling weevil 

Synonyms: Gymnetron antirrhini (Paykull), Gymnaetron antirrhini (Paykull) 

Rhinusa neta (Germar) 

Toadax seed-feeding weevil 

Synonyms: Gymnetron netum (Germar), Gymnaetron netum (Germar) 

Rhinusa antirrhini 

Order Coleoptera 

Family Curculionidae 

Native distributiON Eurasia, Mediterranean 

OrigiNal sOurce USA: Accidental & former Yugoslavia 

CAN: 1917 accidental & former Yugoslavia 

First release USA: 1909 accidental; 1996 intentional 

CAN: 1917 accidental; 1993 intentional 

NONtarget eFFects None reported 

Rhinusa neta 

Order Coleoptera 

Family Curculionidae 

Native distributiON Europe 

OrigiNal sOurce USA: Accidental 

CAN: Accidental 

First release USA: 1937 

CAN: 1957 

NONtarget eFFects None reported 

Description 

Rhinusa antirrhini and R. neta are similar weevils attacking the seeds of toadflaxes in North 

America. Rhinusa antirrhini eggs are oval and flattened. Larvae are C-shaped, creamy yellow 

(Figure 40a) with dark brown head capsules, and are up to 4 mm long. Pupae are dark gray, 

typically 2.5 mm long, and have two tiny ‘horns’ protruding from the top of the thorax (see 

arrow in Figure 40b). Adults are gray to black and covered in dense, short hairs (Figure 40c). 

They have a long, distinctly curved, and pointed snout and a wide body. Adults collected from 

yellow toadflax are typically 2.5-3 mm long, while those developing on Dalmatian toadflax are 

up to 5 mm long. 

Rhinus neta eggs are oval and flattened. Larvae are C-shaped, creamy yellow with light brown 

head capsules, and are up to 4 mm long. Pupae are gray or brown, typically 3 mm long, and 

have two small bumps at the top of the thorax. Adults are gray or brown and covered in dense, 

short hairs (Figure 41a,b). Adult snouts are somewhat blunt and only slightly curved, and are 

not tapered or pointed. Adults are typically 3 mm long. 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

46 Chapter 3: Biology of Toadax Biocontrol Agents

a

a b c

→

→

Figure 40. Rhinusa antirrhini a. arrow points to larva in seed capsule; b. pupa, arrow points to 

‘horns’ on top of the thorax (© Arnold Grosscurt); c. adult (a,c Ivo Toševski, CABI) 

b

Figure 41. Rhinusa neta adults a. (Gyorgy Csoka, Hungary Forest Research Institute, 

bugwood.org); b. (Ivo Toševski, CABI) 

Egg 

Larva 

Pupa 

Adult 

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 

Figure 42. Schematic life cycle of Rhinusa antirrhini and R. neta. Bars indicate the approximate length of 

activity for each life stage; dates will vary depending on local conditions. Black bars represent 

the inactive overwintering period. 

Habitat Preference 

The overall habitat preferences of R. antirrhini and R. neta are unknown. Rhinusa antirrhini is 

distributed throughout most yellow toadflax infestations in North America, indicating it is well 

adapted to a variety of conditions. 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 3: Biology of Toadax Biocontrol Agents 47 

Damage 

Rhinusa antirrhini 

Adult feeding (Figure 43a) is typically insignificant. Female’s egg deposition triggers the 

development of a spur (bump) on the seed capsule (see arrow, Figure 43b). The growing spur 

pushes the R. antirrhini egg into the developing toadflax seeds, triggering the formation of a 

gall. The gall causes the 8-17 seeds closest to the egg to grow up to 10 times their normal size 

and turn a watery, pale yellow color. As a result, attacked capsules can be easily identified 

(Figure 43c). Abnormal seeds are not viable, and larval feeding destroys additional seeds 

within attacked capsules. 

Rhinusa neta 

Adult feeding is typically insignificant. While oviposition and feeding by R. neta does not 

cause seed swelling, a single larva can consume a high proportion of seeds in the capsule. 

For both species, at densities of more than two larvae per capsule, all viable seeds in an attacked 

capsule can be destroyed. Decreasing seed output does not kill existing plants but can help 

reduce the rate of spread and genetic diversity of toadflax populations. 

a b c

→

→

Figure 43. Rhinusa antirrhini a. adults on owers (Eric Coombs, Oregon Department of Agriculture, 

bugwood.org); b. larvae in seeds, yellow arrow points to ‘spur’ while red arrow points 

to a larva (Eric Coombs, Oregon Department of Agriculture, bugwood.org); c. galled, 

swollen seed capsules of yellow toadax (right) and normal seed capsules (left) (© Arnold 

Grosscurt) 

Current Status and Availability 

Rhinusa antirrhini 

This beetle (yellow toadflax biotype) was unintentionally introduced. First reported on yellow 

toadflax in Massachusetts, it has spread naturally and via redistributions throughout North 

America on both yellow and Dalmatian toadflax. An additional strain (Dalmatian biotype) was 

intentionally introduced from former Yugoslavia and released against Dalmatian toadflax in 

Canada and the USA from 1993. 

Rhinusa antirrhini is established on Dalmatian toadflax in the USA and Canada (Figure 44a), 

but it is not as abundant as R. antirrhini on yellow toadflax, and its host impacts have not 

been studied. Rhinusa antirrhini is well established on yellow toadflax throughout the USA 

and Canada (Figure 44b). Larval feeding destroys some seeds in attacked capsules, and seed 

reductions between 85 and 90% have been reported in Washington; however, seed reduction 

is typically much lower. Attack rates from 30-40% in Oregon had minimal impacts on plant 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

48 Chapter 3: Biology of Toadax Biocontrol Agents

density. In Canada, widespread distribution of R. antirrhini has yet to lead to satisfactory 

control. It is believed that the overall impact of R. antirrhini on yellow toadflax is limited, and 

likely also limited on Dalmatian toadflax. 

The impacts of R. antirrhini on hybrid toadflax have not yet been studied in North America. 

a b

Figure 44. North American establishment of Rhinusa antirrhini on a. Dalmatian toadax; b. yellow 

toadax. Note: R. antirrhini is established on yellow toadax in other northeastern and 

northwestern states in the USA not specied in the literature (where yellow toadax is 

established) and has yet to be fully assessed for current distribution within Canada. 

Rhinusa neta 

This beetle was unintentionally introduced and found on both Dalmatian and yellow toadflax 

in the northeastern USA, and it is now established other parts of North America on both yellow 

and Dalmatian toadflax (Figure 45a,b). In the USA, it occurs on both toadflaxes in several 

eastern states and at least Washington in the Northwest, but only in scattered populations. In 

Canada, it is more widespread on yellow toadflax, but only found sporadically on Dalmatian 

toadflax. In both countries, R. neta prefers yellow toadflax over Dalmatian toadflax. Larval 

feeding destroys a high proportion of seeds in attacked capsules, though overall attack rates on 

yellow toadflax are typically limited in the USA. Even in Canada, where yellow toadflax attack 

rates are higher, satisfactory control has yet to be achieved. 

The impacts of R. neta on hybrid toadflax have not yet been studied in North America. 

a b

Figure 45. North American establishment of Rhinusa neta on a. Dalmatian toadax; b. yellow toadax. 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 3: Biology of Toadax Biocontrol Agents 49 

Comments 

At least one parasitic wasp species has been reported to attack R. antirrhini in the USA. 

Competition between Brachypterolus pulicarius and Rhinusa antirrhini/R. neta prevents these 

species from having an additive impact in many locations. 

Rhinusa antirrhini pupae have tiny ‘horns’ that are more pronounced than the small bumps on 

R. neta. Adult R. antirrhini have a more pointed and curved snout than R. neta and are dark 

grayish-black while R. neta adults are a lighter gray to brown. Both R. antirrhini and R. neta 

differ from R. linariae in their location of attack (adults attack flowers and shoot tips and larvae 

attack seeds while R. linariae adults attack stems and larvae attack roots). Mecinus spp. adults 

have more elongated bodies compared to Rhinusa spp. Adult Brachypterolus pulicarius do not 

have the snouts of the Mecinus and Rhinusa weevils. 

Though R. antirrhini was first an accidental introduction in the USA, it is approved for 

redistribution within North America. Because this weevil is already widespread and its overall 

impact is low, it is not a high priority for redistribution. Rhinusa neta is not approved for 

redistribution in the USA. 

Rhinusa linariae Panzer 

Toadax root-galling weevil 

Synonyms: Gymnetron linariae (Panzer) 

Order Coleoptera 

Family Curculionidae 

Native distributiON Europe 

OrigiNal sOurce USA: Germany 

CAN: central southern Europe, Russia 

First release USA: 1996 

CAN: 1996 

NONtarget eFFects None reported 

Description 

Eggs are pale yellow, smooth surfaced, and pear-shaped (Figure 46a). Larvae are C-shaped, 

creamy white with brown head capsules, and are up to 4 mm long. Pupae are dark gray and 

typically 2.5 mm long. Adults are small and black with pronounced, curved snouts (Figure 

46b). They are covered in dense, short hairs. 
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50 Chapter 3: Biology of Toadax Biocontrol Agents

a b

↓ 

Figure 46. Rhinusa linariae a. egg position inside of a root gall on yellow toadax (note arrow) (Ivo 

Toševski, CABI) ; b. adult (Bob Richard, USDA APHIS PPQ, bugwood.org) 

Life Cycle 

Overwintering adults emerge in spring and feed on new toadflax shoots, consuming stem tissue 

and sap. Females lay eggs singly into pockets chewed into toadflax roots and root crowns, 

triggering gall formation. Larvae feed on galled root tissue through three instars. Pupation 

occurs in galls with new adults emerging in mid- to late summer. Adults often feed briefly on 

toadflax stems and then overwinter in soil or plant litter. Some new, fully developed adults 

remain within the root galls throughout the fall and winter, and do not emerge until the following 

spring. There is one generation per year (Figure 47). 

Egg 

Larva 

Pupa 

Adult 

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 

Figure 47. Schematic life cycle of Rhinusa linariae. Bars indicate the approximate length of activity 

for each life stage; dates will vary depending on local conditions. Black bars represent the 

inactive overwintering period. 

Habitat Preference 

The overall habitat preferences of R. linariae in North America are unknown because confirmed 

established populations are restricted to limited sites in British Columbia. In Europe, R. linariae 

does well in grassland habitats, is rarely found in subalpine habitats, and is absent from alpine zones. 

Damage 

In European field studies, between 20 and 100 galls per plant were found on the roots of attacked 

yellow toadflax. Adjacent individual root galls can fuse into gall complexes comprised of up 

to 40 individual galls (Figure 48a,b). Root galls disrupt the transport of nutrients and water 

to and from the roots. Root galls may also act as a metabolic sink, directing root nutrients 

to the developing galls and ultimately to the R. linariae larvae that feed on the gall tissues, 

therefore robbing the toadflax plant of essential nutrients for normal plant growth. Although 

significant gall development can occur, it is not yet known what impact, if any, this agent is 

having on Dalmatian or yellow toadflax populations in the United States and Canada because 

of its limited confirmed establishment to date. 
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Chapter 3: Biology of Toadax Biocontrol Agents 51 

a b

Figure 48. Rhinusa linariae galls on yellow toadax roots a,b (Ivo Toševski, CABI) 

Current Status and Availability 

After the initial USA introductions failed to establish, a population from British Columbia 

was redistributed to Colorado in 2008. This introduction failed as well. Another redistribution 

attempt was made in 2015, though it is too soon to know the fate of this release. To date, R. 

linariae is confirmed as established at a limited number of sites only in British Columbia and 

only on yellow toadflax (Figure 49a,b). Because populations are slow to build, redistributions 

are made whenever possible. Adult foliage feeding and larval galling are known to reduce plant 

nutrient reserves; however, current populations are too low to have a significant impact on 

yellow toadflax populations. The impacts of R. linariae on hybrid toadflax have not yet been 

studied in North America. 

a b

Figure 49. North American establishment of Rhinusa linariae on a. Dalmatian toadax (not established); 

b. yellow toadax 

Comments 

Rhinusa linariae can be differentiated from the other toadflax Rhinusa beetles by the location of 

attack on host plants. Rhinusa linariae adults attack toadflax stems, and their larvae attack the 

roots; R. antirrhini/R. neta adults attack toadflax flowers and shoot tips, and their larvae attack 

the seeds. In addition, R. linariae has a more pointed and curved snout than R. neta and is black 

while R. neta is gray to brown. Mecinus spp. adults have more elongated bodies compared 

to Rhinusa spp. Adult Brachypterolus pulicarius do not have the snouts of the Mecinus and 

Rhinusa weevils. 
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52 Chapter 3: Biology of Toadax Biocontrol Agents

Calophasia lunula (Hufnagel) 

Toadax defoliating moth 

Order Lepidoptera 

Family Noctuidae 

Native distributiON Eurasia 

OrigiNal sOurce USA: Switzerland via Canada 

CAN: Switzerland and former Yugoslavia 

First release USA: 1968 

CAN: 1962 

NONtarget eFFects Multiple species 

Description 

Eggs are pale yellow, strongly ribbed, and slightly conical. Larvae (caterpillars) are gray 

initially but have vivid black and yellow stripes with white spots at the final instar (Figure 

50a). Final instar larvae reach a maximum length of 4.6 cm. Pupae are reddish-brown or golden 

brown within green cocoons (Figure 50b). Adults are a mottled gray-brown with light and dark 

markings on the wings (Figure 50c) and are 1-1.5 cm long with a wingspan of 2.5-3 cm. 

a b c

Figure 50. Calophasia lunula: a. larva; b. cocoon (Gary Piper, Washington State University, bugwood. 

org); c. adult. Top bar length of body, bottom bar wingspan (a,c Laura Parsons & Mark 

Schwarzländer, University of Idaho) 

Life Cycle 

Adult moths emerge in late spring and feed on the nectar of toadflaxes and other plant species. 

Females lay an average of 100 eggs singly on toadflax foliage and, less frequently, on toadflax 

flowers. Larvae feed on young, tender leaves but will consume older and tougher lower stem 

leaves as plants become increasingly defoliated. Larvae nearing the end of the fifth instar move 

to the base of toadflax plants and spin cocoons of silk, chewed leaves, and soil that they attach 

to stem bases, plant litter, or soil. There are 1-3 generations per year, depending on weather 

conditions and the length of the growing season. At northern latitudes and high elevations, 1-2 

generations are most common; three may occur in warmer locales, at lower elevations, and in 

regions with longer growing seasons. The moth overwinters as a pupa within the cocoon. 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 3: Biology of Toadax Biocontrol Agents 53 

Egg 

Larva 

Pupa 

Adult 

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 

Figure 51. Schematic life cycle of Calophasia lunula. Bars indicate the approximate length of activity 

for each life stage; dates will vary depending on local conditions. Black bars represent the 

inactive overwintering period. There are 1-3 generations per year, but most frequently 1-2 in 

North America. 

Habitat Preference 

Calophasia lunula prefers warm, dry sites with coarse-textured soils. Establishment can be 

limited in cold climates, at northern latitudes, and at high elevations. Caterpillars are most 

often found in relatively sparse toadflax infestations. 

Damage 

Severe defoliation of seedlings and one-year-old plants can be fatal; older, larger plants can usually 

rebound from defoliation, although defoliated plants are less vigorous and may produce fewer 

flowers. Complete defoliation of an entire patch of toadflax by this moth has not been documented. 

a b

Figure 52. Calophasia lunula damage: a. larvae feeding on Dalmatian toadax leaves (Laura Parsons 

& Mark Schwarzländer, University of Idaho); b. larvae defoliating a Dalmatian toadax stem 

(Susan Turner, British Columbia Ministry of Forests)(a,b bugwood.org) 

Current Status and Availability 

Although population densities are typically low, this species occurs consistently on both Dalmatian 

and yellow toadflax infestations throughout much of the USA. Localized population explosions 

occasionally occur. Feeding by high densities of early instar C. lunula larvae can cause substantial 

patch defoliation. Overall, larval feeding typically decreases leaf area but does not disrupt the 

photosynthetic capacity sufficiently to have a significant impact on attacked plants. 

Calophasia lunula is established on both yellow and Dalmatian toadflax in southern parts of 

Canada (Figure 53a,b), but its spread north is limited by the colder climates, and its impact is 

limited for the same reasons as in the USA. Parasitism may also limit populations in some parts of 

Canada. The impacts of C. lunula on hybrid toadflax have not yet been studied in North America. 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

54 Chapter 3: Biology of Toadax Biocontrol Agents

a b

Figure 53. North American establishment of Calophasia lunula on a. Dalmatian toadax; b. yellow 

toadax. 

Comments 

Populations may be limited by parasitism, predation, and pathogen outbreaks in some locations. 

Calophasia lunula caterpillars are known to feed and develop on plants related to toadflaxes, 

including non-native ornamentals and one native North American species, Sairocarpus virga. 

Because C. lunula poses a risk to nontarget plant species in the USA, some land managers have 

ceased collecting and redistributing this defoliating moth. Caution should be taken during its 

redistribution, especially in areas with desirable snapdragon species present. 

Eteobalea intermediella Riedl. 

Dalmatian toadax root-boring moth 

Eteobalea serratella Treitschke 

Yellow toadax root-boring moth 

Eteobalea intermediella 

Order Lepidoptera 

Family Cosmopterigidae 

Native distributiON Southern Europe 

OrigiNal sOurce USA: former Yugoslavia 

CAN: Serbia 

First release USA: 1996 

CAN: 1991 

NONtarget eFFects None reported 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 3: Biology of Toadax Biocontrol Agents 55 

Eteobalea serratella 

Order Lepidoptera 

Family Cosmopterigidae 

Native distributiON Southern Europe 

OrigiNal sOurce USA: Italy 

CAN: Italy 

First release USA: 1996 

CAN: 1992 

NONtarget eFFects None reported 

Description 

These species are very similar in appearance, differing most obviously in the surface texture 

of their eggs. The pattern on the surface of E. intermediella eggs is netlike while the surface 

of E. serratella eggs has a ridged appearance, marked by fine parallel lines or furrows (Figure 

54). Larvae (caterpillars) are cream-colored with brown head capsules and are up to 12 mm 

long (Figure 55a). Adults are slender, 8-10 mm long, and are black with white and yellow spots 

(Figure 55c). 

Figure 53. Eteobalea eggs a. E. intermediella; b. E. serratella 

Figure 55. Eteobalea spp. a. E. intermediella larva; b. E. intermediella pupa (both a,b in Dalmatian toadax 

root); c. E. intermediella adult; E. serratella adult (Ivo Toševski, CABI) 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

56 Chapter 3: Biology of Toadax Biocontrol Agents

Life Cycle 

Adults of both species emerge in late spring and live for only a few weeks. Adult moths are 

active from dawn to dusk and do not feed; they spend their entire adulthood mating and laying 

eggs. Eteobalea intermediella lays eggs in loose strings of 3-8 in the lower leaf axils or on 

the base of yellow toadflax and non-flowering Dalmatian toadflax stems. Eteobalea serratella 

lays eggs in loose strings of 3-8 at the base of yellow toadflax stems or on the soil surface. 

Adult females of both species can lay up to 180 eggs. Hatching larvae bore into the root 

crown where they feed on tissue inside tunnels they carve and line with silk. Larvae develop 

through five instars. Mature larvae tunnel back to the root crown or up into the base of a stem 

to construct a cocoon in which to pupate. Eteobalea serratella has one generation per year 

(Figure 56), overwintering as larvae in the roots and pupating the following spring. In contrast, 

E. intermediella typically has two generations per year (Figure 57). New adults emerge in midsummer, quickly mate, and lay eggs. Larvae of this second generation feed inside toadflax roots 

through the fall and winter. Both species pupate within silken cocoons the following spring, 

and adults emerge through a small hole in the base of the stem. 

Egg 

Larva 

Pupa 

Adult 

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 

Figure 56. Schematic life cycle of Eteobalea intermediella. Bars indicate the approximate length of 

activity for each life stage; dates will vary depending on local conditions. Black bars represent 

the overwintering period. There are typically two generations per year. 

Egg 

Larva 

Pupa 

Adult 

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 

Figure 57. Schematic life cycle of Eteobalea serratella. Bars indicate the approximate length of activity 

for each life stage; dates will vary depending on local conditions. Black bars represent the 

overwintering period. 

Habitat Preference 

The overall habitat preferences of Eteobalea intermediella and E. serratella in North America 

are unknown because neither species is known to have established. 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 3: Biology of Toadax Biocontrol Agents 57 

Damage 

The impact of both root-boring moths on toadflax is similar. 

In studies conducted in Europe, three to seven larvae can 

be found within a single root of a toadflax plant, depending 

on the size of the roots. Root tunneling and boring by 

moth larvae does not usually kill toadflax plants directly. 

However, attacked plants are generally less vigorous, have 

fewer flowers, and produce fewer seeds than unattacked 

plants (Figure 58). 

Current Status and Availability 

Despite multiple introductions, neither species is known to 

have established on toadflaxes in North America. 

Figure 58. Eteobalea serratella 

damage to yellow toadax 

(reddish brown dying 

stems) (Ivo Toševski, CABI) 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

58 Chapter 3: Biology of Toadax Biocontrol Agents Table 4. Traits of biological control beetles introduced against toadaxes in North America. Underlined plant species is preferred host.

biOlOgical 

cONtrOl 

ageNt 

speciesattacked 

geNeratiONs/ year 

OverwiNteriNgstage, lOcatiON 

adult 

egg 

larva 

pupa 

Brachypterolus pulicariusToadflax flower-feeding beetle 

Dalmatian, Yellow One Pupae in soil or

plant litter 

Milky white;becoming yellow 

Yellow; brown head capsules;up to 7 mmlong 

Up to 3mm longand 2 mm wide 

Mecinus janthinusYellow toadflax stem-mining weevilMecinus janthiniformisDalmatian toadflaxstem-mining weevil 

M. janthinus: Dalmatian, YellowM. janthiniformis:Dalmatian, Yellow 

One Adults inside

stems 

White; oval C-shaped;

creamy-white;brown headcapsules; up to5 mm long 

Creamy-white;3-5 mm long 

Rhinusa antirrhiniToadflax seed-galling weevil 

Dalmatian, Yellow One Adults in soil or

plant litter; lesscommonly adultsremain in seedcapsules 

Oval; flattened C-shaped:

creamy-yellow;dark brownhead capsules;up to 4 mmlong 

Dark gray;typically 2.5mm long; 2 tiny‘horns’ on top of thorax 

Rhinusa linariaeToadflax root-galling weevil 

Dalmatian, Yellow One Adults in soil;

less commonlyadults remain inroot galls 

Pale yellow;smooth-surfaced;pear-shaped 

C-shaped;creamy white;brown headcapsules; up to4 mm long 

Dark gray;typically 2.5 mmlong 

Rhinusa netaToadflax seed-feeding weevil 

Dalmatian, Yellow One Adults in soil or

plant litter; lesscommonly adultsremain in seedcapsules 

Oval; flattened C-shaped;

creamy yellow;light brownhead capsules;up to 4 mmlong 

Gray or brown;typically 3 mmlong; 2 tinyrounded bumpson top of thorax 

Brachypterolus pulicarius (Daniel K. MacKinnon, Colorado State University); Mecinus spp. (Bob Richard, USDA APHIS PPQ); Rhinusa antirrhini (Ivo Toševski, 

CABI); Rhinusa linariae (Bob Richard, USDA APHIS PPQ); Rhinusa neta (Gyorgy Csoka, Hungary Forest Research Institute) 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 3: Biology of Toadax Biocontrol Agents 59 

Table 5. Traits of biological control moths introduced against toadaxes in North America. Underlined plant species is preferred host.

biOlOgical 

cONtrOl 

ageNt 

speciesattacked 

geNeratiONs/ year 

OverwiNteriNgstage, lOcatiON 

adult 

egg 

larva 

pupa 

Calophasia lunulaToadflax defoliating moth 

Dalmatian,Yellow 

One or two mosttypically; threein some warmlocations withlong growingseasons 

Pupae withincocoons attachedto toadflax stembases, plant litteror soil 

Pale yellow;strongly ribbed;slightly conical 

Gray initially;older larvae withblack and yellowstripes and whitespots; up to 4.6cam long 

Reddish- to golden-brown withingreen cocoons 

Eteobalea intermediella Dalmatiantoadflax root-boringmothEteobalea serratella Yellow toadflax root-boring moth 

E. intermediellaDalmatian, YellowE. serratella; Dalmatian, Yellow 

E. intermdiella

Typically two

E. serratella

One 

Larvae in roots E. intermediella;

surface patternnetlike; E. serratella: surfacepattern furrowedwith ridges 

Cream-colored;brown headcapsules; up to 12mm long 

Slender; blackwith white andyellow spots;8-10 mm long 

Calophasia lunula (Laura Parsons & Mark Schwarzländer, University of Idaho); Eteobalea intermediella (Ivo Toševski, CABI) 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

60 Chapter 3: Biology of Toadax Biocontrol Agents Table 6. Comparison of established toadax biocontrol agent activity according to toadax growth stage (plant and agent stages will vary by climate and location). Month Dalmatian toadflax life stage Yellow toadflax life stage Brachypterolus pulicarius Calophasia lunula Mecinus janthinus Mecinus janthiniformis Rhinusa antirrhini R. neta Rhinusa linariae January Prostrate stems overwinter; seeds continue to disperse from previous year’s stems; new shoots begin sprouting at warm sites Seeds continue to disperse from previous year’s stems; new shoots begin sprouting at warm sites Pupae overwinter in soil or plant litter Pupae overwinter in cocoons attached to toadflax stem bases, plant litter, or soil Adults overwinter within previous year’s toadflax stems Adults overwinter within previous year’s toadflax stems Adults overwinter in soil or plant lit- ter, less commonly adults overwinter within toadflax seed capsules Adults overwinter in soil or plant lit- ter; less commonly adults overwinter within toadflax root galls February March April New shoots sprout from buds on root crown; seeds germinate; flowers begin to form Warm sites: shoots sprout from buds on lateral roots; seeds germinate At warmer sites, adults begin to emerge, feed on young toadflax and lay eggs inside toadflax stems; new larvae feed on toadflax tissue inside short chewed tunnels At warmer sites, adults begin to emerge, feed on young toadflax and lay eggs inside toadflax stems; new larvae feed on toadflax tissue inside short chewed tunnels May Colder sites; shoots sprout, seeds ger- minate; All sites: stems elongate, flowers begin to form Adults emerge and feed on young toadflax; eggs are laid in young toadflax buds Adults emerge and lay eggs on toadflax foliage Adults emerge and feed on young toadflax Adults emerge and feed on young toad- flax; adults lay eggs into toadflax root crowns, triggering gall formation 

June 

Flowers form Flowers form 

Adult emergence and egg laying continue; new larvaefeed on floral/seedtissue 

New larvae feedon toadflax foliage(young leavesattacked first) 

Adults continue toemerge at colder sites; Larvae continue feeding within toadflax stems;pupation begins 

Adults continue toemerge at colder sites; larvae continue feeding withintoadflax stems;pupation begins 

Adults lay eggsinside developingtoadflax flowers;new larvae feed onseed tissue 

New larvae feed ontoadflax galled roottissue July 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 3: Biology of Toadax Biocontrol Agents 61 

Table 6 continued. Comparison of established toadax biocontrol agent activity according to toadax growth stage (plant and agent stages will vary by 

climate and location). 

Month 

Dalmatiantoadflaxlife stage 

Yellow toadflaxlife stage 

Brachypterolus pulicarius 

Calophasialunula 

Mecinusjanthinus 

Mecinusjanthiniformis 

RhinusaantirrhiniR. neta 

Rhinusalinariae 

August 

Flowers and seedsmature; senescencebegins; prostratestems sprout 

Flowers and seedsmature; senescencebegins 

Larvae continuefeeding on floraland seed tissue 

Pupation occurs incocoons near plantbases; new adultsbegin emerging/laying eggs 

New adults emerge in pupal cells, butremain withintoadflax stems 

New adults emerge in pupal cells, butremain withintoadflax stems 

Larvae continuefeeding on seedtissue; pupationbegins in seedcapsules 

Pupation occurs intoadflax root galls 

September 

Larvae drop to thesoil to pupate 

New larvae feed ontoadflax leaves 

Adults overwinterwithin toadflaxstems 

Adults overwinterwithin toadflaxstems 

Pupation finishes;adults emerge from seed capsules tooverwinter in soilor plant litter 

Adults emerge from root galls,feed briefly ontoadflax stems, andoverwinter in soilor plant litter 

October 

Upright stems dieback; prostratestems overwinter;seeds on current-year stemsdisperse 

Stems die back;seeds on current-year stemsdisperse 

Pupae overwinterin soil or plant litter 

Pupation occursin cocoons nearplant bases; pupaeoverwinter 

Adults overwinterin soil or plant litter; less commonlyadults overwinterwithin toadflaxseed capsules 

Adults overwinterin soil or plant litter; less commonlyadults overwinterwithin toadflax rootgalls 

NovemberDecember 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

62 Chapter 3: Biology of Toadax Biocontrol Agents

Prospective Toadax Biological Control Agents 

(Not available as of the publication of this manual, but may become available soon) 

Several potential toadflax biocontrol agents are currently undergoing testing to determine their 

suitability for release in North America. These include five stem-galling weevils. 

Mecinus spp. 

(Coleoptera, Curculionidae) 

Three additional species of Mecinus weevils are currently being evaluated overseas by CABI 

as potential toadflax biocontrol agents. All three closely resemble the currently established 

M. janthinus and M. janthiniformis, but differ in two significant aspects of their life history. 

Eggs laid by the three candidate Mecinus species cause the stem to swell and produce a semigall in which the larva feeds; Mecinus janthinus and M. janthiniformis larval feeding is not 

similarly confined to a gall, so their feeding tunnels are significantly longer. M. janthinus/M. 

janthiniformis adults overwinter in toadflax stems, whereas the candidate Mecinus species 

overwinter as adults in the soil. This difference may aid the overwintering success of the new 

species because they are at a lower risk of temperature fluctuations, drying out, and injury from 

wind and animals. Additional traits of all three weevils are given below. 

Mecinus heydenii Wencker 

Yellow toadflax stem-galling weevil 

Mecinus heydenii has been collected only from yellow toadflax in its native range of Europe, 

Scandinavia, and Russia. Adults emerge in early March from the soil around the previous year’s 

yellow toadflax stems and intensively feed on host shoots. Egg laying begins shortly thereafter, and 

extends over an unusually long period, from mid-March through mid-June. Eggs are deposited in 

the top or middle of actively growing toadflax stems, causing the stems to swell and form semi-galls. 

Larvae feed exclusively on this swollen stem tissue, creating chambers where pupation eventually 

occurs (Figure 59a). Larval feeding results in stunted shoots (Figure 59d). Adults exit host stems 

in early August via a ‘window’, where a thin layer of the outer stem tissue is all that remains after 

larvae chew away the internal gall tissue (Figure 59b). Adult M. heydenii (1.6-2.8 mm long, Figure 

59c) are smaller than both M. janthinus (2.4-3.4 mm) and M. janthiniformis (3.2-6.0 mm). Mecinus 

heydenii has been successfully propagated on a range of hybrid toadflax genotypes in North America 

under quarantine greenhouse conditions, showing promise for release against field hybrids. 

a b c d

Figure 59. Mecinus heydenii attacking yellow toadax a. pupa in stem; b. larval feeding ‘windows’ (left) 

through which adults exit (right); c. adult; d. stunted and deformed stems (a-d Ivo Toševski, CABI) 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 3: Biology of Toadax Biocontrol Agents 63 

Mecinus laeviceps ssp. laeviceps Tournier 

Dalmatian toadflax stem-galling weevil 

Mecinus laeviceps ssp. laeviceps has been collected from Dalmatian toadflax and broomleaf 

toadflax (Linaria genistifolia, closely related to Dalmatian toadflax) in its native range of 

Macedonia, northern Greece, and Montenegro. In their native range, adult M. laeviceps emerge 

much earlier in the growing season and begin laying eggs up to two months earlier than M. 

janthiniformis. Similar to M. janthiniformis, large aggregations of M. laeviceps adults feeding on 

new toadflax shoot growth can result in significant damage to shoot tips and leaves. Eggs (Figure 

60a) are typically deposited within, but near the base of growing toadflax shoots between midApril and the end of May. Egg laying causes swelling of stem tissue, resulting in the formation 

of reddish-colored semi-galls. The larvae of M. laeviceps develop at the base of the toadflax stem 

while the larvae of M. janthiniformis tend to occupy more upper regions of the stem. Following 

pupation, new adults remain in the pupal chamber feeding on the gall tissue until mid-August 

(Figure 60b), when they emerge to overwinter in the soil near their host plant. Adult M. laeviceps 

(2.4-3.3 mm long, Figure 58c) are significantly smaller than M. janthiniformis (3.2-6.0 mm). 

a b c

Figure 60. Mecinus laeviceps ssp. laeviceps a. eggs in a broomleaf toadax stem; b. adults feeding within 

a Dalmatian toadax stem; c. adult male (left) and adult female (right) (a-c Ivo Toševski, CABI) 

Mecinus peterharrisi Toševski & Caldara sp. n. 

Dalmatian toadflax stem-galling weevil 

Mecinus peterharrisi has been collected from both subspecies of Dalmatian toadflax (Linaria 

dalmatica ssp. dalmatica and L. dalmatica ssp. macedonica) in its native range of Macedonia, 

northern Greece, and Montenegro. The life cycle and other biological attributes of M. peterharrisi 

are similar to M. laeviceps; however, M. peterharrisi has been collected from higher elevations than 

M. laeviceps, which may make it better adapted than either M. laeviceps or M. janthiniformis for 

release at North American Dalmatian toadflax sites experiencing colder climates. In their native 

range, M. peterharrisi emerges earlier in the growing season and begins laying eggs up to two 

months before M. janthiniformis. Similar to M. janthiniformis and M. laeviceps, large aggregations 

of M. peterharrisi adults feeding on new toadflax shoot growth can result in significant damage to 

shoot tips and leaves. Eggs are typically deposited near the base of growing toadflax shoots, and 

oviposition causes stem swelling and the formation of semi-galls on host stems. The larvae of M. 

peterharrisi develop at the base of the toadflax stem while the larvae of M. janthiniformis tend to 

occupy the upper part of the stem. Following pupation, new adults remain in the pupal chamber 

feeding on the gall tissue until mid-August (Figure 61a), when they emerge to overwinter in the soil 

near their host plant. Adult M. peterharrisi (2.5-3.7 mm long, Figure 61b) are slightly larger than M. 

laeviceps (2.4-3.3 mm long) but significantly smaller than M. janthiniformis (3.2-6.0 mm). 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

64 Chapter 3: Biology of Toadax Biocontrol Agents

a b

Figure 61. Mecinus peterharrisi a. adult in Dalmatian toadax stem; b. adult male (left) and adult female 

(right) (a,b Ivo Toševski, CABI) 

Rhinusa spp. 

(Coleoptera, Curculionidae) 

Two new species of Rhinusa weevils are currently under consideration as potential toadflax 

biocontrol agents. Both physically resemble the currently established R. antirrhini and R. linariae, 

and are described in greater detail below.

Rhinusa pilosa (Gyllenhal) 

Yellow toadflax stem-galling weevil 

Rhinusa pilosa has been collected from yellow toadflax throughout its native range of northern 

Europe. Adults are black, covered in upright hairs, have a distinctive curved profile (Figure 62a), 

and are up to 4 mm long (excluding the snout) (Figure 62b). In comparison, average R. antirrhini 

and R. linariae adults are approximately 3.0 and 2.5 mm long, respectively. The snout gives this 

weevil a distinctive hook-nosed appearance. In their native range, adult R. pilosa adults emerge 

up to two months earlier in spring compared to the Rhinusa species currently established in 

North America. Eggs are laid in the actively growing tips of yellow toadflax stems, triggering the 

formation of large, obvious galls (sometimes red-tinged) that can be up to 9 mm wide and 20 mm 

long (Figure 63a,b). The galls are nearly fully developed by the time eggs hatch, after which the 

larvae undergo three instars while feeding on the nutrient-rich inner gall tissues before pupating, 

also within the gall. Galls reduce yellow toadflax height, number of stems, and biomass. The 

newly emerged adults also remain in the gall for a period of time in early summer-mid fall and 

feed on remnant gall tissues before chewing their way through the gall wall to exit. Feeding 

continues on host shoots for a brief period before adults move to the soil or litter where they 

become inactive, waiting out periods of intense daytime heat, reduced humidity, and food scarcity. 

These mostly inactive R. pilosa adults may occasionally emerge from temporary refuges in the 

soil or litter to feed on toadflax shoots during cooler, more humid hours in the evening and at 

night. Once temperatures cool consistently in late autumn, adult R. pilosa leave their soil or litter 

refuges and feed extensively on toadflax re-growth before overwintering in soil or plant litter near 

senescing host plants. Adaptations for dealing with environmental challenges, such as summer 

inactivity and overwintering near the ground, make R. pilosa especially attractive for release in 

North America over the wide range of climates where yellow toadflax is invasive. 

Rhinusa pilosa was recommended for release in North America by the Technical Advisory Group 

for Biological Control Agents of Weeds (TAG), but a USA release permit has not yet been granted. 

Canadian regulatory authorities (CFIA) approved the release of R. pilosa in Canada in March 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 3: Biology of Toadax Biocontrol Agents 65 

2014. Limited releases of R. pilosa were made in Alberta and British Columbia, Canada in both 

spring 2014 and 2015, after which successful galling of yellow toadflax was confirmed. There 

also was successful overwintering survival of first generation adults produced from the 2014 

releases. Continued monitoring of the new weevil populations is planned to determine population 

changes, spread, and impact. 

a b

Figure 62. Rhinusa pilosa a. adult on yellow toadax; b. adult male (left) and adult female 

(right) (a,b (Ivo Toševski, CABI) 

a

b

Figure 63. Rhinusa pilosa galls a. development over one week 

(oviposition, 4 days, 7 days); b. mature galls (Ivo Toševski, CABI) 

Rhinusa rara Toševski & Caldara sp.n. 

Dalmatian toadflax stem-galling weevil 

Rhinusa rara is a relatively rare species, but has been collected from Dalmatian and broomleaf 

toadflax (Linaria genistifolia) in its native range of Serbia, Hungary, southern Slovakia, southern 

Czechia, Austria, and southern Russia. Adults are shiny black, covered in flat-laying hairs, have 

a distinctly flattened profile, and are up to 3.8 mm long (excluding the snout) (Figure 64a). 

In comparison, R. antirrhini and R. linariae adults are approximately 3.0 and 2.5 mm long, 

respectively. Similar to R. pilosa, R. rara adults in their native range emerge up to two months 

earlier in spring compared to R. antirrhini and R. linariae in North America. Eggs are laid at the 

base of new toadflax shoots, triggering the formation of galls (Figure 64b,c). Galls formed very 

early in the season suppress any further shoot growth. When R. rara eggs are laid on toadflax 

stems later in the season, gall development is not triggered. Larvae feed exclusively on gall 

tissue. New adults exit galls mid-summer after completing all development within the same gall 

(egg, larva, pupation, adult emergence). Similar to R. pilosa, newly emerged R. rara adults may 

continue to feed sporadically on toadflax through autumn, but are frequently inactive in the hot, 

dry conditions of late summer. Following a brief, but intensive fall feeding period, adult weevils 

overwinter in the soil or plant litter. 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

66 Chapter 3: Biology of Toadax Biocontrol Agents

a b c

Figure 64. Rhinusa rara a. adult; b. gall development over 11 days; c. mature galls in the eld (a-c Ivo 

Toševski, CABI) 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 4: Elements of a Toadax Biological Control Program 67 

CHAPTER 4: ELEMENTS OF A TOADFLAX BIOLOGICAL CONTROL PROGRAM 

Before You Begin 

The results of using biological control to treat toadflaxes vary from site to site for a variety of 

reasons. Land managers should develop treatment programs that complement land use activities 

and management objectives unique to the area. This is accomplished by first understanding the 

scope of the toadflax problem, defining overall goals for the toadflax management program, 

and understanding the control methods available for accomplishing the goals. 

Determining the Scope of the Problem 

Your first step should be to develop a distribution map of toadflaxes at a scale that will allow you 

to address the problem in a manner consistent with your overall land management objectives and 

available weed management resources. The most appropriate scale may encompass a large landscape 

with a variety of site characteristics and land uses managed by many different land owners/managersall of whom contribute to mapping efforts (Figure 65a). In large landscapes with significant 

toadflax infestations and limited mapping resources, aerial mapping of large patches of toadflaxes 

may be sufficient to identify priority areas for additional survey and weed management activities. 

In other management areas with small, discrete toadflax infestations, or where an infestation’s 

characteristics affect your ability to meet management objectives, your weed management strategy 

might have to include more extensive mapping and analysis of the scope of the infestations (e.g. 

size, density, cover, or location in relation to roads and waterways over time) (Figure 65b). 

In many cases, it may prove useful to check for existing toadflax distribution data before collecting 

your own. Several different agencies and organizations maintain weed distribution databases, 

including state agricultural 

departments, provincial 

ministries (e.g. British 

Columbia IAPP Application), 

invasive plant/species councils, 

USDA PLANTS database, 

EDDMapS, and many others. 

EDDMapS can be particularly 

useful for land mangers 

a b interested in creating toadflax 

Figure 65. Dalmatian toadax data for a. counties with Dalmatian toadax in the state of Utah 

(EDDMapS); b. infestations on Antelope Island in the Great Salt Lake, Utah (Becca VanKampen, 

MIA Consulting, EDDMapS) 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

68 Chapter 4: Elements of a Toadax Biological Control Program

distribution maps for their area. By visiting www.eddmaps.org and creating a free account, users 

can view existing distribution maps for toadflaxes or other weeds at the state, county, or point 

level. By selecting the GIS view option, users can view toadflax data on various backgrounds 

and zoomed into different scales, add hand drawn labels, boundaries, points and other shapes 

to the map, perform measurements such as perimeter estimates or distance between points, add 

new toadflax data from user shapefiles, edit the management status of various infestations, and 

print finished maps (see page 90 for more information on EDDMapS). 

Dening Goals and Objectives 

Goals broadly define the “what” or desired outcome of management; objectives define the 

“how” or specific activities through which desired outcomes can be achieved. To be effective, 

objectives must be SMART: specific, measurable, achievable, realistic, and timely. Defining 

your weed management goals and objectives is the crucial first step in developing a successful 

biological control program. By defining what you want to achieve, you will be able to determine 

if, when, and where you should use biological control. 

As precisely as possible, you must define what will constitute a successful toadflax management 

program. For example, the objective of “. . . a noticeable reduction in toadflax density over 

the next ten years . . . ” might be achievable, but it uses a subjective measurement of success 

that is open to observer bias. Alternatively, the objective of “. . . a 50 percent reduction in 

toadflax stems over the next three years . . .” is objectively measurable (and therefore SMART). 

If your goal is to reduce the abundance of toadflaxes, then biological control might be an 

appropriate weed management tool; however, by itself biological control will not completely 

and permanently remove toadflaxes from the landscape. If your goal is to eradicate toadflaxes, 

then you should plan to employ other weed control techniques instead of, or in addition to, 

biological control (see Chapter 5 for more details). 

Understanding Toadax Management Options 

Once you determine the scope of your toadflax infestations and define your overall program 

goal and objectives, review the weed control methods available (biological control, physical 

treatments, cultural practices, and herbicides), and determine the conditions (when, where, if, 

etc.) under which it might be appropriate to use each method or combination of methods (see 

Chapter 5). Consult commercial, agency, or university biological control experts, cooperative 

weed management area partners, or county weed coordinator/supervisors to learn about other 

toadflax management activities (herbicide use, grazing, etc.) underway or planned for your 

area, and the level and persistence of control that might be achieved by each. 

Identify the resources that will be available for weed management activities, and determine if 

they will be consistently available until you meet your weed management program objectives. 

If resources are not currently available, or will not be available consistently, identify what will 

happen at the treatment site if planned management activities are not implemented or are not 

completed. This information will help you determine the best management activities to use as 

you initiate and continue your integrated toadflax management program. 

With a map of toadflax infestations in your management area, an understanding of your land 

management goals, well defined weed management objectives, and a list of the weed control 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 4: Elements of a Toadax Biological Control Program 69 

methods available with the level of control you can realistically expect from each, you can 

identify sites where biological control would be a good fit, alone or in combination with other 

control methods. 

Developing, Implementing, and Managing a Toadax Biological 

Control Program 

When biological control is deemed suitable for treating your toadflax infestations, there are 

several important factors to consider. These include selecting appropriate release sites, obtaining 

and releasing biocontrol agents, and monitoring the success of the program. Familiarity with 

all aspects of a biocontrol program before beginning will greatly facilitate its implementation 

and increase its chances of success. These items are discussed in their own sections below. If 

problems are encountered following the initiation of a toadflax biological control program, 

refer to the troubleshooting guide in Appendix I for potential solutions. 

Selecting Biological Control Agent Release Sites 

Establish goals for your release site 

Consider your overall management goals for a given site when you evaluate its suitability for 

the release of biological control agents. Suitability factors will differ depending on whether the 

release is to be a: 

1. general release, where biological control agents are simply released for toadflax management, 

2. field insectary (nursery) release, used primarily to mass produce biological control agents for 

redistribution to other sites, or 

3. research release, used to investigate biological control agent biology and/or the agent’s impact 

on the target weed and nontarget plant community. 

A site chosen to serve one of the roles listed above may also serve additional functions over time 

(e.g., biological control agents might eventually be collected for redistribution from a research or 

general release). 

Determine site characteristics 

For practical purposes, no toadflax infestation is too large for biocontrol releases; however, it 

might not be large enough (Figure 66a). Very small, isolated patches of toadflaxes may not be 

adequate for biological control agent populations to build up and persist and are often better 

off treated with other weed control methods, such as herbicides or physical control. Toadflax 

infestations of at least 4 acres (1.6 hectares) are typically the minimum size recommended for 

biological control releases, but larger infestations are more desirable (Figure 66b), especially if 

the land manager hopes to someday use the release site as a field insectary. Biocontrol agents 

disperse more easily in contiguous toadflax infestations than in infestations with only a few 

scattered plants and distant patches. If your biological control program goals involve 

evaluating the program’s efficacy, establish permanent monitoring sites before you release any 

biocontrol agents. Monitoring sites require regular inspections, so consider the site’s ease of 

accessibility, terrain, and slope. 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

70 Chapter 4: Elements of a Toadax Biological Control Program

a b

Figure 66. Toadax infestations a. too small for biological control (Hal Pearce, USDA FS); b. 

appropriate size for biological control (Sharlene E. Sing, USDA FS RMRS) 

Note land use and disturbance factors 

Release sites should experience little to no regular disturbance. Abandoned fields/pastures and natural 

areas are good choices for biological control agent releases. Sites where insecticides are used should 

not be utilized for biocontrol agent releases. Such sites include those near wetlands that are subject to 

mosquito abatement, rangelands that are subjected to grasshopper control, or near agricultural fields 

or orchards where pesticide applications occur regularly. Roadside infestations along dirt or gravel 

roads with heavy traffic should also be avoided; extensive dust makes toadflax plants less attractive to 

biocontrol agents and silica may kill larvae. Do not use sites where significant land use changes will 

take place, such as road construction, cultivation, building construction, and mineral or petroleum 

extraction. If supply of biocontrol agents is limited, prioritize release sites that are not regularly burned 

or treated with herbicides. 

Survey for presence of biological control agents 

Always examine your prospective release sites to determine if toadflax biological control agents are 

already present. If an agent you are planning to release is already established at a site, you can still 

release it at that site to augment the existing population. If populations already appear to be abundant, 

then it may be better to make the release at another site. Re-evaluate planned releases if another species 

of biological control agent is already present; e.g. competition between Brachypterolus pulicarius and 

Rhinusa antirrhini/R. neta prevents these species from having an additive impact in many locations. 

Consider releasing a biocontrol agent known to be more effective, such as the toadflax stem miners M. 

janthinus or M. janthiniformis, on sites where less effective, widely distributed agents as B. pulicarius, 

Rhinusa antirrhini and Calophasia lunula are already established. 

Record ownership and access 

If you release biological control agents on private land, it is a good idea to select sites on land likely 

to have long-standing, stable ownership and management. Stable ownership will help you establish 

long-term agreements with a landowner, permitting access to the sites to sample or harvest biological 

control agents and collect insect and vegetation data for the duration of the project. This is particularly 

important if you are establishing a field insectary site, because five years or more of access may be 

required to complete insect harvesting or data collection. General releases of biological control agents 

to control toadflax populations require less-frequent and short-term access; you may need to visit such 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 4: Elements of a Toadax Biological Control Program 71 

a site only once or twice after the initial release. When releasing biocontrol agents on private land, it 

may be a good idea to obtain the following: 

• written permission from the landowner allowing use of the area as a release site, 

• written agreement with the landowner allowing access to the site for monitoring and collection 

for a period of at least six years (three years for establishment and buildup and three years for 

collection), 

• permission to put a permanent marker at the site, and 

• written agreement with the landowner that land management practices at the release site will not 

interfere with biological control agent activity 

The above list can also be helpful for releases made on public land where the goal is to establish 

an insectary. In particular, an agreement should be reached that land management practices will 

not interfere with biological control agent activity (e.g. spraying or physically destroying the weed 

infestation). It is often useful to visit the landowner or land manager at the release site annually to 

ensure they are reminded of the biological control endeavors and agreement. 

You may wish to restrict access to release locations, especially research sites and insectaries, and allow 

only authorized project partners to visit the sites and collect insects. The simplest approach is to select 

locations that are not easily visible to or accessible by the general public (Figure 67a). To be practical, 

most if not all of your sites will be readily accessible, so in order to restrict access you should formalize 

arrangements with the landowner or manager. This will require you to post no-trespassing signs, install 

locks on gates, etc. (Figure 67b). 

Another consideration is physical access to a release site. You will need to drive to or near the release 

locations, so determine if travel on access roads might be interrupted by periodic flooding or inclement 

weather. You might have to accommodate occasional road closures by private landowners and public 

land managers for other reasons, such as wildlife protection. 

Choosing the Appropriate Biological Control Agents for Release 

You should consider several factors when deciding which biological control agent to release at 

a site, including agent efficacy, availability, and site preferences (Table 7). 

Figure 67. Methods for discouraging biocontrol agent release site access a. being very dicult to 

approach (Jesse Young, USDA FS RMRS); b. posting “no disturbance” sign (Alan Martinson, 

Latah County Weed Control & Paul Brusven, Nez Perce BioControl Center) 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

72 Chapter 4: Elements of a Toadax Biological Control Program Table 7. Summary of general characteristics and site preferences of toadax biological control agents established in North America Agent Characteristics Site characteristics

SpecieS 

part 

attacked 

efficacy 

availability 

favorableconditionS 

Unfavorable conditionS 

Brachypterolus pulicariusToadflax flower-feeding beetle 

Flowers Prefers yellow toadflax, on

which it delays floweringand reduces seed production.Though abundant, its overallimpact is minimal. 

Widespread in the USA and CAN, but because it has lowimpact, it is a low priority forredistribution. 

Well adapted to a variety of conditions throughoutthe majority of toadflaxinfestations in NorthAmerica. 

No specific unfavorable conditionsdetermined todate. 

Calophasia lunulaToadflax defoliating moth 

Leaves Widespread but usually in 

low densities on yellow andDalmatian toadflax in theUSA and CAN. High densities cause heavy defoliation, butmature plants usually recover. 

Limited throughout the NorthAmerican Northwest and inON, NB, and NS. Becauseit has low impact, and mayattack desirable snapdragons,it is a low priority for redistribution. 

Warm, dry sites with coarse-textured soils.Frequently found insparse toadflax infestations. 

Cold climates,northern latitudes,high elevations,dense toadflaxinfestations. 

Mecinus janthiniformisDalmatian toadflaxstem-mining weevil 

Stems, leaves,shoot tips 

Successful in warmer intermountain climates. Miningand adult feeding significantlydecrease Dalmatian toadflaxpopulations in the USA and CAN (Southern Interior, British Columbia). Like to traveluphill 

Common through parts of theNorth American Northwest. 

Well adapted to a variety of conditions; wintertemperatures lower than-18.5° F (-28° C) causetemporary populationreductions. 

Cold climatesand regions withfluctuating springtemperatures (e.g.eastern slope ofRocky Mountains)less ideal, thoughpopulations canrebound fromkilling wintertemperatures. 

Mecinus janthinusYellow toadflax stem-mining weevil 

Stems, leaves,shoot tips 

Populations are still limited.Mining and adult feedingdecrease yellow toadflax populations locally in the USAand still under study in CAN.Like to travel uphill. 

Limited distribution on sitesthroughout the North American Northwest and in NovaScotia. Populations are smallbut increasing; adults readily disperse to colonize newplants/patches. 

Mild, low-elevationsites, though successfulpopulations have beenobserved above 7,000feet (2,180 m). 

Still being determined for NorthAmerica, thoughlikely to includecold climates. 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 4: Elements of a Toadax Biological Control Program 73 

Table 7 continued. Summary of general characteristics and site preferences of toadax biological control agents established in North America 

Agent Characteristics Site characteristics

SpecieS 

part 

attacked 

efficacy 

availability 

favorableconditionS 

Unfavorable conditionS 

Rhinusa antirrhiniToadflax seed-galling weevil 

Seeds Prefers yellow toadflax, on

which it reduces seed production. Despite its highabundance, overall impact islimited. 

Limited on Dalmatian toadflaxin the Northwest and in Ontario. Widespread on yellow toadflax in northern USA and southern CAN. Because it haslow impact, it is a low priorityfor redistribution. 

Well adapted to a variety of conditions throughoutthe majority of toadflaxinfestations in NorthAmerica. 

No specific unfavorable conditionsdetermined todate. 

Rhinusa linariaeToadflax root-galling weevil 

Roots Prefers yellow toadflax on

which it reduces plant nutrientreserves. Established in BConly, its populations are too low for significant impact. 

Populations are very limitedand established only in BCCAN to date. Insufficient forredistribution. 

Largely unknown because of its low establishment. In Europe, itdoes best at low elevation sites. 

Unknown, possibly high elevationsites. 

Rhinusa netaToadflax seed-feeding weevil 

Seeds Prefers yellow toadflax, on

which it reduces seed production. Despite its highabundance, overall impact islimited. 

Limited on yellow toadflaxand even more so on Dalmatian toadflax in the USAand CAN. Not approved forredistribution in the USA. 

Unknown Unknown 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

74 Chapter 4: Elements of a Toadax Biological Control Program

Biocontrol agent ecacy 

Efficacy refers to the ability of the biological control agent to directly or indirectly reduce the 

population of the target weed below acceptable damage thresholds or cause weed mortality 

resulting in control. It is preferable to release the most effective biocontrol species rather than 

releasing all available biocontrol species against the target weed. Consult with local weed 

biological control experts, neighboring land managers, and landowners to identify the agent(s) 

that appear(s) more effective given local site characteristics and management scenarios. 

Biocontrol agent availability 

The toadflax root moths, Eteobalea spp., are not known to have established in North America. 

All seven of the remaining toadflax biocontrol agents described in this manual are established, 

though their availability varies greatly between species and sites. Mecinus janthiniformis is 

currently the most effective Dalmatian toadflax biocontrol agent, and is readily available for 

collection throughout the northwestern USA and the Southern Interior of British Columbia. 

Mecinus janthinus prefers yellow toadflax, and though it is currently less widespread than 

M. janthiniformis, populations of M. janthinus are increasing in parts of northwestern North 

America. The toadflax defoliating moth, Calophasia lunula, is established on both Dalmatian 

and yellow toadflax at multiple locations in the USA and Canada, though its abundance and 

impact are typically limited. The toadflax root-galling weevil, Rhinusa linariae, is established 

only in British Columbia, and populations are limited. The flower- and seed-feeding beetles 

Brachypterolus pulicarius and R. antirrhini are widespread on their hosts in North America; 

however, their low impact and wide distribution make them low priorities for redistribution. 

The seed-feeding beetle R. neta is more limited in its distribution throughout North America; 

however, it has low impact and is also not approved for redistribution in the USA. 

Federal and state/provincial departments and commercial biological control suppliers may be 

able to assist you in acquiring agents not yet available but permitted for use in your area 

(see Obtaining and Releasing Toadflax Biological Control Agents, below). In the USA, state 

departments of agriculture, county weed managers, extension agents, or federal and university 

weed biological control specialists should be able to recommend in-state sources. 

Release site characteristics 

General physical site and biological preferences for each agent have been developed from 

anecdotal observations and experimental data. These are listed in Table 7 to help land managers 

ensure that insects are released in sites with suitable conditions. 

Obtaining and Releasing Toadax Biological Control Agents 

You can obtain toadflax biological control agents by collecting or rearing them yourself, having 

someone collect them for you, or by purchasing them from a commercial supplier. This section 

provides information on collecting and purchasing toadflax biocontrol agents, with emphasis on 

Mecinus janthinus and M. janthiniformis. The toadflax root-galling weevil, Rhinusa linariae, 

is currently less available in the field. Brachypterolus pulicarius, Calophasia lunula, and R. 

antirrhini are already widespread and have limited impact, so are not highly recommended for 

redistribution. R. neta is not approved for redistribution in the USA. 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 4: Elements of a Toadax Biological Control Program 75 

a 

Factors to consider when looking for sources of biological control agents 

You do not need to take a “lottery approach” and release all available biological control agents at 

a site in the hopes that one of them will work. In fact, some biological control agents will not be 

available even if you want them (e.g. Eteobalea spp.), and some have been shown to have little 

or no effectiveness in certain areas (e.g Brachypterolus pulicarius and Rhinus antirrhini). The 

best strategy is to release the best agent! Ask the county, state, provincial, or federal biological 

control experts in your area for recommendations of agents for your particular project. 

If available, biological control agents from local sources are best. Using local sources increases 

the likelihood that biocontrol agents are adapted to the climate and site conditions present and 

are available at appropriate times for release at your target infestation. Using locally sourced 

agents also reduces the possibility of accidentally introducing biocontrol agent pathogens 

or natural enemies to your area. Local sources may include neighboring properties or other 

locations in your and adjacent counties/districts. Remember that in the USA, interstate transport 

of biological control agents requires a USDA-APHIS-PPQ permit (see Regulations Pertaining 

to the Transfer of Toadflaxes Biological Control Agents, page 88). Get your permits early to 

avoid delays. 

Some USA states, counties, and universities have “field days” at productive insectary sites 

(Figure 68a,b). On these days, land managers and landowners are invited to collect or receive 

freshly collected toadflax biological control agents for quick release at other sites. These 

sessions are an easy and often inexpensive way for you to acquire biological control agents. 

They are good educational opportunities as well, because you can often see first-hand the 

impacts of various biocontrol agents on toadflax plant communities. 

Typically, field days are conducted at several sites in a state and on several dates. Although 

designed for intrastate collection and redistribution, out-of-state participants may be welcome 

to participate (remember that USDA permits are required for interstate movement and release 

of biological control agents). Contact county weed supervisors, university weed or biological 

control specialists, or federal weed managers for information about field days in your region. 

Collecting Toadax Biological Control Agents 

Planning and timing of collection is critical. For all species, it is usually most efficient to 

scout the potential collection site well in advance to ensure your desired species is present at 

suitable densities. The species of biological control agent and weather characteristics at your 

b 

Figure 68. Toadax eld days a. yellow toadax (Sharlene E. Sing, USDA FS RMRS); b. Dalmatian 

toadax (Melissa Griths, Madison Valley Ranchlands) 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

76 Chapter 4: Elements of a Toadax Biological Control Program

collection and release site will determine the best time in the season to collect. Ensure that all 

necessary collection supplies are on hand. Also, accurate identification of the biological control 

agents is essential. General guidelines for collecting toadflax biological control agents are listed 

below and in Table 8. 

For all species, collect only on a day with good weather. Do not collect in the rain; insects will 

hide and become difficult to find in rainy weather, excess moisture causes health problems, and 

biocontrol agents may drown in wet collection containers. As a general rule of thumb, biocontrol 

agent populations are large enough to permit redistribution collections if the number of insects 

recommended for an initial release can be harvested in a fairly short period of time (less than an 

hour). For example, if 200 adult weevils are recommended for a stem-mining weevil release, you 

should be able to easily collect several hundred adult weevils in about 30 minutes or less from a 

collectible population. If it takes several hours to collect 200 weevils, then the population is not 

large enough to support redistribution collections. There is generally no danger of over-collecting 

at an established site, provided 1) collections stop when it becomes difficult to find insects; and 

2) collections are made once or, at most, only a few times during a season. 

Collection methods 

Tray sampling, hand picking, aspirating, sweep netting, and transferring biocontrol agentinfested plant material are commonly used methods for collecting toadflax biocontrol agents. 

The most appropriate method will depend on the physical characteristics of the insect, the 

density of the insect population, time of year, time available for collecting, and available 

personnel. Regardless of the method used, it is most effective to collect biocontrol agents and 

release them on the same host species (i.e. if collecting from Dalmatian toadflax, release the 

collected individuals on Dalmatian toadflax). 

Tray sampling: The tray sampling method is the most efficient way to collect adult beetles 

(Brachypterolus pulicarius, Mecinus spp., and Rhinusa spp.), especially when their populations 

are high. Using your hand or a short stick, gently tap the plant, knocking the beetles from the 

plant into a plastic tray or tub (Figure 69a,b). Choose a tub or tray appropriate for the size of the 

plants/position of agents on the plants: for example, if you need to capture M. janthiniformis 

adults sheltering in leaf axils all along the length of a tall Dalmatian toadflax stem, a larger 

sized tub or tray will be required than for collecting M. janthinus from stunted yellow toadflax 

plants. Avoid disturbing the toadflax before tapping because this will often cause most beetles 

to drop to the ground. Cover or frequently shake the tray or tub to prevent biocontrol agents 

from escaping, and sort the agents prior to shipping (see below). 

Hand picking: Hand picking is required for collecting easily damaged insects such as the 

larvae of Calophasia lunula. Flexible forceps, which bend around larvae without injuring them 

as traditional tweezers would, are typically used to pluck agents from toadflaxes. In some 

cases it may be easier and more productive to break off a section of host plant where insects 

are aggregated, rather than collect them on an individual basis. Small paintbrushes (e.g., those 

used for art projects) are also useful for delicate hand picking jobs with small larvae or eggs. 

Aspirating: An aspirator is a device used to suck insects from a surface into a collection 

vial. Aspirators can be used to collect insects out of a sweep net or off a sorting tray (both 

described below), out of a sorting cage, or to collect adults of B. pulicarius, Mecinus spp., 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 4: Elements of a Toadax Biological Control Program 77 

Table 8. Recommended timetable and methods for collecting toadax biological control agents in North America. Methods are listed in the order of ease of 

collection. 

biocontrol 

agent 

biocontrol 

agent 

Stage 

toadflax 

plant 

Stage 

timing 

method 

noteS 

Brachypterolus pulicariusToadflax flower-feeding beetle 

Adults Stems bolting to early

flowering 

May to June Aspirate or hand-pick

adults from inside flowers,or collect using a sweep netor tray. 

Though approved for redistribution, it is already widespread with low impact, so is not ahigh priority for redistribution.

Calophasia lunulaToadflax defoliating moth 

Larvae (caterpillars) Stems early flowering

to mature 

Mid-June throughSeptember 

Hand pick larvae fromplants 

Limited impact makes lowpriority for redistribution.Reports of nontarget attack; redistribute with caution.

Eteobalea intermediellaDalmatian toadflax root-boring mothEteobalea serratellaYellow toadflax root-boring moth 

N/A N/A N/A N/A Despite multiple releases,

these species have not beenconfirmed as established inNorth America. 

Mecinus janthiniformisDalmatian toadflax stem-mining weevil 

Adults Stems bolting

to flowering 

Adults: April to late June; Infested Stems: fall-earlyspring 

Tray sampling, sweep netting, or moving M. janthiniformis-infestedstems to uncolonized weedpatches 

Already widespread, butshould be redistributed toDalmatian toadflax populations where not currentlyestablished. 

Mecinus janthinusYellow toadflax stem-mining weevil 

Adults Stems bolting

to flowering 

Adults: late March to midJune depending on climaticregion; Infested stems:fall-early spring 

Tray sampling, sweep netting, or moving M. janthinus-infested stems touncolonized weed patches 

Not widespread and shouldbe redistributed to yellowtoadflax populations where notcurrently established.

Rhinusa antirrhiniToadflax seed-galling weevil 

Adults Stems bolting

to flowering 

May to mid-June Tray sampling, sweep 

netting, or aspirating adultsfrom flowers 

Though approved for redistribution, it is already widespread with low impact, so is not a

high priority for redistribution.

Rhinusa linariaeToadflax root-galling weevil 

Adults Stems bolting

to flowering 

May Tray sampling or sweep 

netting 

Failure to determine establishment at many release sitesand low impact of establishedpopulations make this a lowpriority for redistribution.

Rhinusa netaToadflax seed-feeding weevil 

N/A N/A N/A N/A This species is not

approved for redistributionwithin the USA. 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

78 Chapter 4: Elements of a Toadax Biological Control Program

a b 

Figure 69. Tray sampling to collect toadax biocontrol agents a. (Sharlene Sing, USDA FS 

RMRS); b. (Carol Bell Randall, USDA FS) 

and Rhinusa spp. directly from toadflax plants. A variety of aspirators can be purchased from 

entomological, forestry, and biological supply companies, or you can construct one yourself. 

Aspirators are powered by mouth suction, manually by using an aspirating bulb (Figure 70a), 

or mechanically using a modified hand vacuum (Figure 70b). Inline filters are commercially 

available to prevent unintentional inhalation or swallowing of debris or insects during mouth 

aspiration. At the very least, mouth aspirators should be equipped with fine-mesh screening on 

the vial end of the tubing held in the mouth so that insects and small particles are not inhaled 

(Figure 70a). In some cases, biocontrol agents might be abundant enough to collect with a 

specialized insect vacuum (Figure 70c). 

Sweep netting: A sweep net consists of a conical canvas or muslin bag held open on one 

end by a sturdy wire hoop 10-15 inches in diameter (25-38 cm) attached to a handle 3 feet 

long (0.9 m, Figure 71a). Insects are ‘swept’ off toadflax plants and accumulate in the closed 

(narrow) end of the conical net. Sweep nets can be purchased from entomological, forestry, and 

biological supply companies, or you can construct them yourself. Heavy-duty nets and rigorous 

sweeping are required to dislodge biocontrol agents from toadflaxes. However, many beetles 

will fail to fall into the net. Sweeping also breaks off many shoots, killing any Mecinus eggs 

and larvae contained inside. Sweeping is not a recommended method for collecting toadflax 

agents because it can significantly reduce the number of Mecinus offspring emerging on swept 

sites in following year(s). 

a b c 

Figure 70. Aspirators for collecting toadax biocontrol agents a. mouth aspirator with inline HEPA 

lter, bulb, and collection vial indicating release density ll levels; b. modied hand vacuum 

aspirator (Carol Bell Randall, USDA FS); c. motorized backpack aspirator (a,c Sharlene E. Sing, 

USDA FS RMRS) 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 4: Elements of a Toadax Biological Control Program 79 

b c

A sweep is made by swinging the net through the upper plant canopy and collecting insects off the 

foliage. It is best to use no more than 25 sweeps before removing the biocontrol agents from the net. 

Removing insects at regular intervals reduces the harm that could result from knocking biocontrol 

agents around with debris, and reduces opportunities for predatory insects and spiders swept up 

with the biocontrol agents to find and devour the biocontrol agents. It is often helpful to dump the 

contents of the sweep net into a shallow tray or basin to facilitate sorting by aspirating biocontrol 

agents from debris and other insects in the net. 

Transferring agent-infested plant material: This method is applicable for the Mecinus weevils. 

Because adults overwinter within toadflax stems, infested stems can be cut, bundled (Figure 71b), 

and moved to new sites where the weevils are not yet established. Stems can be collected from late 

fall through early spring. However, all collected stems must then be retained under consistently cold, 

moist conditions (9°C or 48°F at ~60% humidity) to keep agents alive and discourage them from 

leaving the stems, until host plants begin growing on release sites the following spring. If you use 

this method, always remove roots, seed capsules and loose seeds to eliminate the spread of toadflax 

propagules (seeds and root buds) to new sites as this can introduce new toadflax genetic material. 

Sorting: Tray sampling, sweep netting, and vacuum sampling are not selective collection methods, 

so other insects and spiders are usually collected along with the biocontrol agents. Sorting separates 

the biocontrol agents from unwanted insects, other organisms and debris, such as weed seeds, 

collected along with the biocontrol agents. The easiest way to sort is to empty the contents of 

the net or tray into a plastic tub and aspirate the toadflax biocontrol agents out of the debris. If 

the collected material is first chilled in a cooler, the insects will move more slowly and will be 

easier to catch and sort. Use an aspirator (described above) to sort the biocontrol agents (Figure 

72a,b). To speed up the sorting process, count out a set number of agents 2-5 times (for example, 

200 or 500 adult Mecinus spp. weevils) into separate collecting vials. Tap the bottom of vial to 

knock down all the weevils, then mark the fill level on the vial. Use the average fill level based on 

those 2-5 collection vials to collect approximate release-size densities of agents without needing 

to count out each individual insect. Remember that M. janthinus adults are smaller than M. 

janthiniformis adults, so different release density fill levels need to be used for these two species. 

a 

Figure 71. Toadax biocontrol agent collection methods a. sweep net (Laura Parsons, University of 

Idaho, bugwood.org); b. 50-stem bundles of Mecinus-infested yellow toadax stems (top) 

and Dalmatian toadax stems (bottom)(after removing all roots, seed capsules, and loose 

seeds); c. the same 50-stem bundles of Dalmatian toadax stems (left) and yellow toadax 

stems (right) shown in 71b, with stems fanned out on one end to facilitate the dispersal of 

emerging adult Mecinus spp. (b,c Sharlene E. Sing, USDA FS RMRS) 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

80 Chapter 4: Elements of a Toadax Biological Control Program

a b 

Figure 72. Sorting toadax biocontrol agent collections a. in the eld with mechanical 

aspirators and trays (Carol Bell Randall, USDA FS); b. in a cage with a mechanical 

aspirator (Sharlene E. Sing, USDA FS RMRS) 

Collection methods by species 

Toadflax flower-feeding beetle: (Brachypterolus pulicarius): Collect adult beetles. Adults 

are easily collected by aspirating individual beetles from inside the flowers and from stem 

tips. Adults can also be collected using the tray sampling method if their populations are 

large. Sweeping the tops of plants is a slower, more destructive, and less selective method 

for collecting adults. Depending on location, the best time to collect adult beetles is May 

to June, when they have emerged from overwintering sites and are actively feeding, 

aggregating near the tops of the plants, and mating. The best time of day to collect adults is 

mid- to late morning, when they are active but still moving slowly. Adult beetles are very 

sensitive to heat; hot afternoons cause them to seek shaded niches. This beetle is already 

widespread throughout North America, but has a low overall impact on toadflax populations. 

Consequently, it is not a high priority for redistribution. 

Toadflax defoliating moth: (Calophasia lunula): When collecting the defoliating moth, it 

is better to collect the larvae. Although care still needs to be taken when collecting larvae, 

the adult moths are substantially more fragile and difficult to find. Gently pick larvae off of 

plants by hand or with the aid of flexible forceps that were designed to prevent the crushing 

of soft-bodied larvae, carefully dislodge them into shallow plastic tubs, or just break off and 

collect toadflax shoots where multiple early-instar larvae are feeding. Larger caterpillars may 

regurgitate a green liquid when handled; this is a normal defensive response and does not 

indicate the caterpillar is injured. Larvae will frequently drop from the plant when approached 

or touched. Sweeping is not advised because it will injure the larvae. Young larvae will be 

found on young foliage or flowers; older larvae are found on larger leaves or stems. It is 

important not to place too many larvae (less than 50) in a container as overcrowding may result 

in cannibalism. Ensure that collecting bins and shipping containers are well provisioned with 

healthy toadflax leaves and kept cool because larvae are heat sensitive. Caterpillars can be 

collected from mid-June through September. Because of concerns about the host specificity 

of this insect and its tendency to disperse widely from its point of release, we do not 

recommend collecting the defoliating moth for redistribution, particularly in the USA. 

Toadflax stem-mining weevils (Mecinus janthinus/M. janthiniformis): Collect adult beetles. 

Adults are collected by tapping plants over tubs or trays to dislodge the insects, or by sweeping 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 4: Elements of a Toadax Biological Control Program 81 

the tops of toadflax plants. Tray sampling is preferable to sweeping because sweeping can break 

off shoots with eggs and larvae developing inside, which reduces the number of adults that can 

emerge the following spring. Choose a tub or tray appropriate for the size of the plants/position 

of agents on the plants: for example, if you need to capture abundant Mecinus janthiniformis 

adults sheltering in leaf axils all along the length of a tall Dalmatian toadflax stem, a larger 

sized tub or tray will be required than for collecting M. janthinus from stunted yellow toadflax 

plants. At peak densities, several thousand M. janthiniformis adults can be collected in 2-3 

hours. Depending on location, the collecting period is generally from late April through June 

when adults have emerged from overwintering in last year’s stems and are actively feeding and 

mating on the top portions of new toadflax shoots. Mecinus janthinus adults can be collected 

slightly earlier than M. janthiniformis adults. 

Because adults overwinter within attacked toadflax stems, infested plants can also be cut, 

bundled, and moved to new sites where the weevils are not yet established. When releasing 

by transferring toadflax stems infested with Mecinus spp., begin by confirming that agent 

population densities are high by splitting 10-20 stems randomly selected throughout the 

collection site. If most stems evaluated contain more than 2 adults, carefully harvest entire 

stems, keeping them as intact as possible by cutting them off at soil level with gardening 

pruners. Gently remove seed capsules, brush away any loose seeds and soil, and cut off all root 

material at the collecting site. Assemble bundles of 20-50 stems that are tied with kitchen twine 

at each end of the bundles (Figure 71b). Transport bundles loosely stacked in plastic bins fitted 

with lids. Do not allow stems to become warm or dried out during transportation or storage. 

Stems can be collected from fall through early spring but must be stored under consistently 

cold, moist conditions (9°C or 48°F with ~60% humidity) to keep agents alive and discourage 

them from leaving the stems prematurely. Once host plants in the field begin spring growth, 

release Mecinus by cutting the binding on one end of the stem bundle so that the stems can 

be fanned out and the bundle can be placed upright within a dense stand of uncolonized host 

plants. Failing to cut binding from one end of the bundle can prevent adult Mecinus in interior 

stems from successfully exiting the bundle. Precautions must be taken to eliminate the spread 

of toadflax propagules (seeds and root buds) to new sites as this can introduce new toadflax 

genetic material. Though this method requires a large effort, it can be useful for transferring M. 

janthinus to uncolonized yellow toadflax infestations due to the relatively limited establishment 

of M. janthinus in North America. Stem transfers can also be useful for both yellow and Dalmatian 

toadflax infestations that occur at high elevations where toadflax plant development is often 

delayed. Adult Mecinus spp. emergence on low elevation toadflax can occur too early to be used 

for making biocontrol releases on high elevation sites. The stem transfer method is therefore also 

a useful alternative for making later season releases on high elevation toadflax infestations. 

Toadflax seed-galling weevil (Rhinusa antirrhini): Collect adult beetles. Adults are collected 

by tapping plants over tubs or trays to dislodge the insects, or by sweeping the tops of toadflax 

plants. Aspirating individual adults or mating pairs from plants is possible but slow and laborious. 

Collect the seed-galling weevils during the heat of the day. The optimal time to collect is the period 

between the appearance of flower buds and the onset of flowering. Mating pairs aggregate at the 

top of plants, and are easily seen. Depending on location, the collecting period is generally from 

May to mid-July when adults are actively feeding and mating on the top portions of plants. More 

beetles are collected from yellow toadflax than from Dalmatian toadflax. This beetle is already 

widespread throughout North America, but has a low overall impact on toadflax populations. 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

82 Chapter 4: Elements of a Toadax Biological Control Program

a 

Consequently, it is not a high priority for redistribution. A related species, the toadflax seedfeeding weevil Rhinusa neta, is not approved for redistribution in the USA. 

Toadflax root-galling weevil (Rhinusa linariae): Only a few known populations are believed 

to be established in Canada, so this weevil is largely unavailable at this time. When collections 

are deemed possible, this should only be done under the guidance of the appropriate Canadian 

authority. Generally adult beetles are collected throughout May when they are actively feeding 

and mating on the top portions of plants but before females move to the bases of the plants to 

oviposit. Tapping weevils into collection trays or tubs is the recommended collection method. 

Release Containers for Toadax Biological Control Agents 

The manner in which biological control agents are handled during transportation to the release 

site will affect whether they will survive and multiply at the new site. To reduce mortality or 

injury, it is best to release biocontrol agents the same day they are collected. 

Following collection, biocontrol agents need to be transferred to release containers intended to 

protect them (and to prevent insects from escaping en route). Release containers should be rigid 

enough to resist crushing but also ventilated to provide adequate airflow and reduce condensation. 

Un-waxed paperboard cartons are ideal; they are rigid, permeable to air and water vapor, and are 

available in many sizes. As an alternative, you can use release containers made of either lightcolored lined or waxed paper (e.g., ice cream cartons are particularly suitable, see Figure 73a) or 

plastic, providing they are ventilated; simply poke numerous holes in the container or its lid with 

an ordinary push pin or thumb tack (Figure 73b), and cover larger holes with a fine mesh screen 

or fabric. Untreated paper bags (lunch bags) work well for transporting biocontrol agents short 

distances; however, they are fragile and offer little physical protection for the material within, 

must be sealed tightly to prevent biocontrol agents from escaping, and some biocontrol agents 

are capable of chewing through them. Do not use glass or metal release containers; they are 

breakable and make it difficult to regulate temperature, airflow, and humidity. 

b 

Figure 73. Containers for transporting toadax biocontrol agents a. cardboard release containers 

(Martin Moses, University of Idaho, bugwood.org); b. plastic container with pinholes for 

ventilation on the sides, containing Mecinus janthiniformis and Dalmatian toadax sprigs 

(Sharlene E. Sing, USDA FS RMRS) 
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Chapter 4: Elements of a Toadax Biological Control Program 83 

Fill release containers half full with crumpled paper towels or tissue paper to provide a substrate 

for biocontrol agents to rest on and hide in, and to help regulate humidity. Fill the other half 

with toadflax sprigs. Sprigs must be inspected to ensure they are free of seeds, flowers, dirt, 

spiders, and other insects and should not be placed in water in the release container. Seal the 

release container lids either with masking tape or label tape. If you are using paper bags, fold 

over the tops several times and staple them shut. Be sure to label each container with (at least) 

the biological control agent(s) name, the collection date and site, and the name of the person(s) 

who did the collecting. 

Transporting Toadax Biological Control Agents 

Keep the containers cool at all times: If you sort and package the biocontrol agents while in 

the field, place the release containers in large coolers equipped with frozen ice packs. Do not 

use ice cubes unless they are contained in a separate, closed, leak-proof container. Wrap the ice 

packs in crumpled newspaper or bubble wrap to prevent direct contact with release containers 

and to absorb any condensation that forms. Place extra packing material in coolers to prevent 

ice packs from shifting and damaging biocontrol agent containers. As an alternative to coolers 

with ice packs, electric car-charged coolers may be utilized, provided the cycle is set to cool 

and not warm. Always keep coolers out of direct sun, and only open them when you are ready 

to remove the biological control agent containers to place them in a refrigerator for overnight 

storage or to release the biocontrol agents. If you sort and package your agents indoors, keep 

them in a refrigerator (no lower than 40°F or 4.4°C) until you transport or ship them (which 

should occur as soon as possible but no longer than 48 hours). 

Transporting short distances: If you can transport your biocontrol agents to their release sites 

within 3 hours after collection, and release them the same day or early the next, you need not 

take any measures other than those already described. 

Shipping long distances: If you will be shipping your insects to their final destination, use a bonded 

carrier service with guaranteed overnight delivery (e.g., USPS, FedEx, UPS, or DHL) and send 

the recipient the tracking number for the package. In such cases, the release containers should 

be placed in insulated shipping containers with one or more ice packs. Some specially designed 

foam shippers have pre-cut slots to hold biocontrol agent containers and ice packs (Figure 74). 

This construction allows cool air to circulate but prevents direct contact between the ice and 

the release containers. Laboratory and medical 

suppliers sell foam “bioshippers” that are used 

to transport medical specimens or frozen foods. 

If neither foam product is available, you can use 

a heavy-duty plastic cooler. Please note that 

for safety reasons, dry ice cannot be used for 

transporting biocontrol agents. 

Careful packaging is very important regardless 

of the shipping container you use. Ice packs 

need to be wrapped in crumpled newspaper, 

wrapping paper, or bubble wrap, and should be Figure 74. Commercially made shipping container 

firmly taped to the inside walls of the shipping (University of Idaho, bugwood.org) 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

84 Chapter 4: Elements of a Toadax Biological Control Program

container to prevent them from bumping against and possibly crushing the release containers during 

shipping. Empty spaces in the shipping container should be loosely filled with crumbled or shredded 

paper, bubble wrap, packing “peanuts,” or other soft, insulating material. Use enough insulation to 

prevent release containers and ice packs from shifting during shipment, but not so much that air 

movement is restricted. Tape the release container lids shut. Enclose all paperwork accompanying 

the biocontrol agents (including copies of permits and release forms) before sealing the shipping 

container. For additional security and protection, you may place the sealed shipping containers or 

coolers inside cardboard boxes. 

Other factors to consider 

• Make overnight shipping arrangements well before you collect your biological control agents, 

and make sure the carrier you select can guarantee overnight delivery. 

• Plan collection and packaging schedules so that overnight shipments can be made early in 

the week. Avoid late-week shipments that may result in delivery on Friday through Sunday, 

potentially delaying release of the agents for several days. 

• Clearly label the contents of containers and specify that they are living insects. 

• Check with a prospective courier to make sure that they can accept this type of cargo and will 

not treat the packages in ways that could harm the biological control agents. If the courier 

cannot guarantee that such treatments will not occur, choose a different carrier. 

• Contact personnel at the receiving end, tell them what you are shipping and when it is due to 

arrive, provide a tracking number, verify that someone will be there to accept the shipment, and 

instruct them not open the container prior to releasing the agents. 

Common Packaging Mistakes 

Crushing- Secure all material included in the shipping container so that blue ice, bundles of plant 

material, etc. do not become loose and move around in transit thereby crushing, tearing or popping 

open release containers and killing or scattering the biocontrol agents inside. 

Escape- Tape release containers securely with masking or other easily removable/resealable tape to 

prevent agents from escaping into the shipping container. 

Excess heat- Do not expose release containers to direct sunlight or temperatures above 80°F (27°C). 

Avoid shipping delays that can expose agents to high temperatures. 

Excess moisture- Remove spilled or excess water in release and shipping containers. Do not ship 

weed sprigs with any type of water source (e.g., floral foam or tubes) inside release containers; use 

only a small square of new, well-rinsed, moist but not damp cellulose sponge. Add crumpled paper 

towels to release containers to absorb incidental moisture or condensation. 

Lack of ventilation- Provide adequate ventilation; use air-permeable release containers or make air 

holes in plastic containers with push pins or other small diameter tools. 

Starvation- Provide sufficient food, and do not store release containers with biological control 

agents more than 48 hours. Larval Calophasia lunula eat constantly so they need to be shipped with 

abundant foliage. 

Stress- Provide root-, flower- and seed-free sprigs of the target weed (free also of other weed 

species’ seeds, flowers, dirt, spiders, or other insects) and crumpled paper towels where biocontrol 

agents can shelter; avoid over-crowding. 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 4: Elements of a Toadax Biological Control Program 85 

a 

Purchasing Toadax Biological Control Agents 

A number of commercial suppliers provide toadflaxes biological control agents. In the USA, county 

weed managers, extension agents, or university weed or biological control specialists may be able to 

recommend one or more suppliers. Make sure that a prospective supplier is reputable, can provide 

copies of required permits, can provide healthy individuals of the species you want (parasite- and 

pathogen-free), and can deliver them to your area at a time appropriate for field release (you will 

want to know where and when the biocontrol agents were collected). Avoid purchasing agents from 

a supplier who collects biocontrol agents from an environment significantly different from your 

planned release location. Interstate shipments of toadflax biological control agents by commercial 

suppliers also require a USDA permit, a copy of which should be enclosed in the shipping box 

(see page 88). Confirm in advance that there is a permit in place for the species you are acquiring 

as well as the region in which the release will occur. DO NOT purchase or release unapproved 

or non-permitted biological control organisms. Note that before any agents can be taken across 

national borders, whether collected or purchased, an importation permit from the regulatory 

agency of the receiving country is required (USDA-APHIS in the USA and CFIA in Canada). 

Releasing Toadax Biological Control Agents 

Establish permanent location marker: Place a steel fence post or plastic/fiberglass pole as a marker 

at the release point (Figure 75a). Avoid wooden posts; they are vulnerable to weather and decay. 

Markers should be colorful and conspicuous. Bright orange or pink are superior to red, blue, yellow 

and green, which can blend into surrounding vegetation. Where conspicuous posts may encourage 

vandalism, mark your release sites with short, colorful plastic tent/surveyor’s stakes or steel plates 

that can be tagged with release information and located later with a metal detector and GPS. 

Record geographical coordinates at release point using GPS: Map coordinates of the site 

marker should be determined using a global positioning system device (GPS) or a GPScapable tablet/smartphone. There are numerous free apps available for recording GPS 

coordinates on a tablet/smartphone (Figure 75b). Coordinates should complement but not 

replace a physical marker. Accurate coordinates will help re-locate release points if markers 

are damaged or removed. Along with the coordinates, be sure to record what coordinate 

system and datum you are using, e.g., latitude/longitude in WGS 84 or UTMs in NAD83. 

Prepare map: The map should be detailed and describe access to the release site, including roads, trails, 

and relevant landmarks. 

Use your vehicle’s trip 

odometer to measure 

and record mileage 

between specified 

locations on your map, 

e.g., when you turn on 

to a new road, at cattle 

guards along the route, 

and where you park. The b 

map should complement 

but not replace a 

physical marker and 

Figure 75. Biocontrol agent release site tools a. permanent marker; b. 

smartphone with free weed and biocontrol agent mapping app 

iBioControl (a,b Rachel Winston, MIA Consulting) 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

86 Chapter 4: Elements of a Toadax Biological Control Program

GPS coordinates. Maps are especially useful for long-term biological control programs in which 

more than one person will be involved or participants are likely to change. Maps are often necessary 

to locate release sites in remote locations or places physically difficult or confusing to access. 

Complete relevant paperwork at site: Your local land management agency/authority may have 

standard biocontrol agent release forms for you to complete. Typically, the information you provide 

includes a description of the site’s physical location, including GPS-derived latitude, longitude, 

and elevation; a summary of its biological and physical characteristics and land use; the name(s) of 

the target weed and biocontrol agent(s) released; date and time of the release; weather conditions 

during the release; and the name(s) of the person(s) who released the agents (see Sample Biological 

Control Agent Release Form in Appendix II). The best time to record this information is while you 

are at the field site. Consider using a smartphone and reporting app such as iBioControl. This free 

application uses EDDMapS (see page 90 for more information) to help county, state, and federal 

agencies track releases and occurrences of biological control agents of noxious weeds. Once back 

in the office, submit the information to your local weed control office, land management agency, or 

other relevant authority/database. Always keep a copy for your own records. 

Set up photo point: A photo point is used to visually document changes in toadflax infestations 

and the plant community over time following the release of biocontrol agents. Use a permanent 

feature (landmark) in the background as a reference point (e.g., a mountain, large rocks, trees, or a 

permanent structure) and make sure each photo includes your release point marker. Avoid capturing 

images that mostly show only the target weed without reference points that can identify specific 

release sites. Pre- and post-release photographs should be taken from roughly the same place and at 

the same time of year (Figure 76a,b). Label all photos with the year and location. 

a b 

Figure 76. Multi-year photos of a Dalmatian toadax biocontrol agent release site at Oster, Idaho 

utilizing permanent geographical features in the background and taken from roughly 

the same place and time in both years a. 2003; b. 2010 (a,b Joseph Milan, BLM/ISDA) 

Release as many agents as possible: As a general rule of thumb, it is better to release an adequate 

number of individuals of a biocontrol agent species on one toadflax infestation than it is to spread 

those individuals too thinly over multiple toadflax infestations. Releasing all the agents within a 

release container in one spot will help ensure that a sufficient number of males and females can find 

one another to reproduce; this also reduces the risks of inbreeding and other genetic problems. An 

optimal release of the defoliating moth, Calophasia lunula, would consist of at least 100 larvae; 

however, redistributions of this biocontrol agent are not recommended because of nontarget feeding 

concerns. Generally for toadflax beetles, a minimum release of 200 insects is recommended to 

establish a population. You may want to release 500 or more beetles if you want to establish an 

insectary site for future collecting. 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 4: Elements of a Toadax Biological Control Program 87 

Often, a single release will be sufficient to establish an insect population, especially if a large 

number (500 or more) of insects were released. The only way to determine if biocontrol agents 

have established is to inspect them annually for up to 5 years (or more) after releases were made. 

Subsequent releases may be necessary if initial releases fail to establish. For species or locations 

where establishment is likely to be slow (e.g. due to high levels of overwintering mortality), planning 

to make releases on the same site for 2 or 3 consecutive years may increase successful establishment 

and reduce the time until agent impact on target weed populations is seen. If more than one release 

is available in a given year, be sure to put some distance between releases; 1 km (2⁄3 mile) is ideal. 

If possible, make more than one release per drainage or in adjoining drainages; if one of your 

releases is wiped out by flooding, fire, herbicide application or other catastrophic disturbance, then 

biocontrol agents from adjoining releases can repopulate it. Strategically releasing biocontrol agents 

in adjoining weed infested drainages can over time lead to sustainable, effective suppression of 

toadflaxes at a landscape level. 

Mecinus spp. weevils typically travel uphill rather than downhill to colonize uninfested host plants, 

so releases of this biocontrol agent should be made at the bottom of weed infested hillsides. When 

releasing by transferring toadflax stems infested with Mecinus spp., remove the ties on one end of 

each bundle. Fan out the stems at the loose end of the bundle so adult weevils can easily escape 

from the stems (Figure 71c). Deposit bundles into dense patches of toadflax on uncolonized sites. 

In general, you can release biocontrol agents either in open or caged releases. Caged releases prevent 

immediate dispersal of biocontrol agents but require you to put up and take down equipment. For 

open releases, get to the desired release location, open the release container, and gently shake out 

all insects and toadflax stems and foliage in one small area (Figure 77a). Do not scatter biocontrol 

agents throughout the infestation. Do not walk back overthe area where you just made a release. 

Make sure the toadflax stems in the release container do not have any immature or mature seeds on 

them before dumping them out at the new site. Gently dislodge any insects hiding in or clinging to 

the paper towels in the release containers. For caged releases, place a mesh bag over a toadflax plant 

or a caged area containing multiple plants (Figure 77b), release insects into the cage, and secure the 

bottom of the cage to either the stem or the ground. Cages confine the insects for a period of time 

so they adjust to the site and easily find one another. Cages should be removed after a few weeks to 

prevent them from being vandalized or damaged by animals or weather. 

It is most effective to collect biocontrol agents and release them on the same host species (i.e. 

if collecting from Dalmatian toadflax, then release those onto Dalmatian toadflax. Releases of 

all biocontrol agents should be made under moderate weather conditions (mornings or evenings 

a b 

Figure 77. Releases of Mecinus spp. a. open release of M. janthiniformis on Dalmatian toadax 

(Curt Leibrand, USDA FS RMRS); caged release of M. janthinus on yellow toadax 

(Carol Bell Randall, USDA FS) 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

88 Chapter 4: Elements of a Toadax Biological Control Program

of hot summer days, mid-day for cold season releases). Making releases under these conditions 

reduces the immediate dispersal of stressed agents when they are dumped out of release containers; 

appropriately timed releases can significantly enhance the probability of establishment. If you 

encounter an extended period of poor weather, however, it is better to release the insects than 

wait three or more days for conditions to improve as the agents’ vitality may decline with 

extended storage. Do not worry if it snows after you made your release – biocontrol agents 

are well adapted to most field conditions and cold, wet conditions are preferable to hot, dry 

conditions for making releases. Avoid transferring biocontrol agents to areas with obvious ant 

mounds or signs of ground dwelling animals that may prey upon biological control agents. 

Regulations for the Transfer of Toadflax 

Biological Control Agents 

USA, intrastate 

Generally, there are few if any restrictions governing collection and shipment of approved biological 

control agents within the same state; however, you should check with your state’s department of agriculture or agriculture extension service about regulations governing the release and intrastate transport 

of your specific biological control agent. The state of California regulates release permits at the county 

level. 

USA, interstate 

The interstate transportation of biological control agents is regulated by the U.S. Department of Agriculture (USDA), and a valid permit is required to transport living biological control agents across state 

lines. You should apply for a Plant Protection and Quarantine (PPQ) permit from the Animal and Plant 

Health Inspection Service (APHIS) as early as possible—but at least six months before actual delivery 

date of your biological control agent. You can check the current status of regulations governing intrastate shipment of weed biological control agents, PPQ Form 526 at the USDA-APHIS-PPQ website. 

The permit process can be accessed by doing an Internet search for “USDA APHIS 526 permit application”. This allows the complete online processing of biological control agent permit requests. 

Canada 

Canada requires an import permit for any new biological control agent or shipments from overseas of 

previously released agents. Permits are issued by the Plant Health Division of the Canadian Food Inspection Agency. Redistribution within a province (or even within Canada) of weed biological control 

agents that have been officially approved for use in Canada is generally allowed; however, you should 

consult with provincial and federal authorities and specialists prior to moving any weed biological 

control agent between areas (e.g., from the prairies to the interior or coast of British Columbia). Accidentally introduced biocontrol agents that have become adventive in a region, or native organisms that 

may feed on a weed targeted for control should not be moved to new areas without consulting federal 

authorities and specialists as their host range or potential ecological impacts are not fully known. 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 4: Elements of a Toadax Biological Control Program 89 

Documenting, Monitoring, and Evaluating a Biological Control Program 

The Need for Documentation 

The purpose of monitoring is to evaluate the success of your toadflax biological control 

program and to determine if you are meeting your weed management goals. Documenting 

outcomes (both successes and failures) of biocontrol release programs will help generate a 

more complete picture of biocontrol impacts, guide future management strategies, and serve 

education and public relations functions. Monitoring can provide critical information for other 

land managers by helping them predict where and when biological control might be successful, 

helping them avoid releasing ineffective biocontrol agents or the same biocontrol agent in 

an area where they were previously released, and/or helping them avoid land management 

activities that would harm local biocontrol agent populations or worsen the toadflax problem. 

(See the Code of Best Practices for Classical Biological Control of Weeds on page 5.) 

Monitoring activities utilize standardized procedures over time to assess changes in populations 

of the biocontrol agents, toadflaxes, other plants in the community, and other components of 

the community. Monitoring can help determine: 

• If biological control agents have become established at the release site 

• If biological control agent populations are increasing or decreasing, and how far they have 

spread from the initial release point 

• If biological control agents are having an impact on toadflaxes 

• If/how the plant community or site factors have changed over time 

Monitoring methods can be simple or complex. A single year of monitoring may demonstrate 

whether or not the biocontrol agents established, while multiple years of monitoring may allow 

you to follow the population of the biocontrol agents, the decline of the target weed, changes 

in the plant community, and changes in other factors such as climate or soil. 

Information Databases 

Many federal and state/provincial departments have electronic databases for archiving 

information about weed biological control releases. We have included a standardized biological 

control agent release form that, when completed, should provide sufficient information for 

inclusion in any number of databases (see Appendix II). 

At the federal level in the USA, the USDA Animal and Plant Health Inspection Service 

(APHIS) maintains the Cooperative Agricultural Pest Survey (CAPS) database, which is part 

of the National Agricultural Pest Information System (NAPIS). Biological control agent release 

information is entered into CAPS by a number of state and federal agency personnel who serve 

on the state’s CAPS survey committee. Contact your local APHIS officials or state department 

of agriculture for more information on participation. Similarly at the federal level in Canada, 

Agriculture and Agri-Food Canada maintains a database of initial releases of all biocontrol 

agents permitted by CFIA for use. 

The USDA Forest Service maintains a database of biological control agent releases on federal 

and non-federal lands. As of the writing of this document, weed biocontrol agent releases made 

on Forest Service lands are entered into the Forest Service ACtivity Tracking System (FACTS) 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

90 Chapter 4: Elements of a Toadax Biological Control Program

database. Other agencies may maintain their own databases for this information. Many of 

the databases maintained by state and federal agencies have safeguards in place to prevent 

exploitation of the information they contain. 

The USDA Forest Service (in conjunction with the University of Georgia, MIA Consulting, 

University of Idaho, CAB International, and the Queensland Government) also maintains a 

worldwide database for the Biological Control of Weeds: A World Catalogue of Agents and 

their Target Weeds. The database includes entries for all weed biocontrol agents released 

through 2014, including the year of first release within each country, the biocontrol agents’ 

current overall abundance and impact in each country, and more. This database can be accessed 

at www.ibiocontrol.org/catalog/. 

EDDMapS (Early Detection & Distribution MAPping System) is a web-based mapping 

system increasingly being used for documenting invasive species as well as biocontrol agent 

distribution in North America. EDDMapS combines data from existing sources (e.g. databases 

and organizations) while soliciting and verifying volunteer observations, creating an inclusive 

invasive species geodatabase that is shared with educators, land managers, conservation 

biologists, and beyond. Information can be added in online forms through home computers 

and/or apps created for smartphones. For more information on how to utilize or contribute to 

these tools, visit www.eddmaps.org and apps.bugwood.org. 

Monitoring Methods 

There are three main components to measure in a toadflax monitoring program: biological 

control agent populations, toadflax populations, and the rest of the plant community (including 

nontarget plants). More detailed monitoring might also examine effects on other biotic 

community components (such as other insects, birds, mammals, etc.) or abiotic factors (such 

as erosion, soil chemistry, etc.). Only the three main monitoring components are discussed in 

this manual. 

Assessing biological control agent populations: If you wish to determine whether or not 

toadflax biocontrol agents have established after initial release, you simply need to find the 

agents in one or more of their life stages, or evidence of their presence (Table 9). Begin looking 

for biocontrol agents where they were first released, and then expand to the area around the 

release site. 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 4: Elements of a Toadax Biological Control Program 91 

Table 9. Life stages/damage to look for to determine establishment of toadax biological control agents (Eteobalea spp. are not included as these root moths 

have not been conrmed as established in North America). a. Brachypterolus pulicarius adults congregating on toadax buds and owers (Susan Turner, British Columbia Ministry of Forests); b. B. pulicarius larva (Daniel K. MacKinnon, Colorado State University); c. Calophasia lunula cocoon (Gary Piper, Washington State University); d. C. lunula larvae defoliating toadax (Laura Parsons & Mark Schwarzländer, University of Idaho); e. M. janthiniformis adult feeding damage on foliage (Carol Bell Randall, USDA FS); f. M. janthiniformis larval mines in toadax stem (Laura Parsons, University of Idaho); g. Mecinus spp. adult (Bob Richard, USDA APHIS PPQ); h. yellow toadax dying from M. janthinus larval mining (Sharlene E. Sing, USDA FS RMRS); i. Rhinusa antirrhini adults on toadax owers; j. R. antirrhini larvae in swollen seed capsules (i-j Eric Coombs, Oregon Department of Agriculture); k. R. linariae adult (Bob Richard, USDA APHIS PPQ); l. R. linariae galls on yellow toadax stem (Ivo Toševski, CABI); m. R. neta adult (Gyorgy Csoka, Hungary Forest Research Institute)

agent 

life Stage 

Where to 

look 

When to 

look 

What to 

look 

for 

appearance 

Brachypterolus pulicariusToadflax flower-feeding beetle 

Adults Toadflax shoot tip leaves and buds; flowers May to June 

Feeding damage (holes) in the side offlowers, or on shoot tips leaves andbuds; adults congregating on toadflaxbuds and flowers to lay eggs 

Larvae Inside toadflax flowers June to September 

Larvae feeding within flowers onpollen, anthers, ovaries and immatureseeds 

Calophasia lunulaToadflax defoliating moth 

Adults 

Toadflax stem bases, plant litter, soil beneath toadflax plants 

August through April 

Cocoons made of silk, chewed leavesand soil attached to stem bases, plantlitter, or soil 

Larvae Toadflax foliage June to September 

Extensive defoliation of upper halfof shoots; groups of actively feedinglarvae on foliage; feeding damagefocused on the edge of leaves. 

Mecinus janthiniformisDalmation toadflax stem-mining weevil 

Adults Toadflax shoot tips, foliage April to late June 

Intense shot-hole feeding damagefocused on foliage and buds at tops ofstems; adults congregating on leavesand stems to mate and lay eggs. 

Larvae Inside toadflax stems May to July 

Larvae mining inside stems; deadplants; plants with shoot tips curledand leaning over, stunted growth and limited flowering. 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

92 Chapter 4: Elements of a Toadax Biological Control Program

agent 

life Stage 

Where to 

look 

When to 

look 

What to 

look 

for 

appearance 

Mecinus janthinusYellow toadflax stem-mining weevil 

Adults Toadflax shoot tips, foliage March to mid-June 

Minor shot-hole feeding damage ontoadflax foliage; adults congregatingon upper leaves and stems to mate andlay eggs. 

Larvae Inside toadflax stems April to late June 

Larvae mining inside stems; deadplants; plants with twisted shoot tips,stunted growth, and limited flowering 

Rhinusa antirrhini Toadflax seed-galling weevil 

Adults Toadflax shoot tips, buds, flowers May to mid-July Feeding damage on flowers or shoot tips; adults congregating on toadflax buds and flowers to lay eggs 

Larvae Inside toadflax flowers July to August 

Spur on swollen seed capsules; swollen, watery pale seeds; larvae feedingon seeds. 

Rhinusa linariaeToadflax root-galling weevil 

Adults Toadflax shoots, root 

crowns May Feeding damage on stems; adults con- gregating at root crowns to lay eggs. 

Larvae Galled tissue of toadflax roots June to July Galls extending downward from toadflax root crowns; larvae feeding in galled tissue 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 4: Elements of a Toadax Biological Control Program 93 

agent 

life Stage 

Where to 

look 

When to 

look 

What to 

look 

for 

appearance 

Rhinusa netaToadflax seed-feeding weevil 

Adults Toadflax shoot tips, buds, flowers May to mid-July Feeding damage on flowers or shoot tips; adults congregating on buds and flowers to lay eggs 

Larvae Inside toadflax flowers July to August 

Larvae feeding within seed capsuleson immature seeds (neither the seedcapsules nor the seeds are swollen) 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

94 Chapter 4: Elements of a Toadax Biological Control Program

Populations of some biocontrol agents may take two to three years to build to detectable levels. 

If no biocontrol agents are detected a year after release, it does not mean they failed to establish. 

Revisit the site at least once annually for three years. If no evidence of biocontrol agents is 

found, either select another site for release or make additional releases at the monitored site. 

Consult with your county extension educator or local biological control of weeds expert for 

assistance. 

A systematic monitoring approach is required to determine the changing densities of biocontrol 

agent populations. The Standardized Impact Monitoring Protocol (SIMP) is one such approach 

to monitoring biocontrol agent populations, weed populations, and the surrounding plant 

community over time (Appendix III). This protocol was cooperatively developed by the Bureau 

of Land Management, the University of Idaho, USDA Forest Service Forest Health Protection, 

the Nez Perce Biocontrol Center, and the Idaho State Department of Agriculture. SIMP 

was designed to be simple, efficient, and sufficiently versatile to allow for the collection of 

information from the same sites over multiple years. The SIMP method can be easily modified 

to meet your personal or agency needs for toadflaxes. For example, rather than counting adult 

Mecinus spp. during repeated sweep intervals, one could count the number of Calophasia 

lunula larvae (or any other agent species-life stage combination) present on toadflax foliage 

during a timed interval. An alternative general toadflax biological control agent monitoring 

form can be found in Appendix IV. Feel free to modify existing data sheets by adding extra 

columns, descriptive classes, etc. to satisfy your monitoring needs. 

Assessing the status of toadflaxes and co-occurring plants: The ultimate objective of a toadflax 

biological control program is to permanently reduce the abundance of toadflaxes and enable 

the recovery of more desirable vegetation on the site. To determine the efficacy of biocontrol 

efforts, there must be monitoring of plant community attributes, such as target weed distribution 

and density. Ideally, monitoring begins before biological control efforts are started (pre-release) 

and at regular intervals after release. There are many ways to qualitatively (descriptively) or 

quantitatively (numerically) assess weed populations and other plant community attributes at 

release sites. 

Qualitative (descriptive) vegetation monitoring: Qualitative monitoring uses subjective 

measurements (words, images, or objects) to describe toadflaxes and the rest of the plant 

community at the management site. Examples include listing plant species occurring at the 

site, estimating density, age and distribution classes, visual infestation mapping (as opposed 

to mapping with a GPS unit), and a series of photos from designated photo points through 

time (Figure 78a,b). See Appendix V for a sample data form where you can record qualitative 

toadflax monitoring data along with information on associated vegetation. Qualitative 

monitoring provides insight into the status or change of toadflaxes populations. However, its 

descriptive nature does not generally allow for detailed statistical analyses. Data obtained in 

qualitative monitoring may trigger more quantitative monitoring later. 

Quantitative vegetation monitoring: Quantitative monitoring measures changes in the toadflax 

population as well as the vegetative community as a whole before and after a biocontrol agent 

release using numbers and statistics. It may be as simple as counting the number of toadflax 

stems in a small sample area, or as complex as measuring toadflaxes plant height, flower and 

seed production, biomass, species diversity, and species cover (Figure 79a,b). 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 4: Elements of a Toadax Biological Control Program 95 

a b 

Figure 78. Dalmatian toadax infestation with large populations of Mecinus janthiniformis 

a. in 2010; b. in 2011 in Idaho County, Idaho (a,b Rachel Winston, MIA 

Consulting) 

a b

Figure 79. Monitoring a. measuring toadax density; b. estimating toadax cover 

(Sharlene E. Sing, USDA FS RMRS) 

Quantitative sampling data can be more readily analyzed using statistical methods and 

demonstrate significant plant community changes. Pre- and post-release monitoring should 

follow the same protocol and be employed at the same time of year. Post-release assessments 

should be planned annually for at least three to five years after the initial biocontrol agent 

release. 

The SIMP approach described earlier and found in Appendix III is a combination of qualitative 

and quantitative monitoring elements. See Appendix VI for a sample data form where you can 

record qualitative toadflax monitoring data along with information on associated vegetation. 

Assessing impacts on nontarget plants: To address possible nontarget attacks on species related 

to toadflaxes, you must become familiar with the plant communities present at and around your 

release sites and be aware of species present that are related to toadflaxes. Start by compiling 

a list of the Plantaginaceae species present that are closely related to the Linaria, including 

native and exotic species of snapdragons, and native toadflaxes in the genus Nuttallanthus. You 

may need to consult with local, state, or regional botanical experts, or review local herbarium 

records for guidance on areas where related nontarget plants might be growing and additional 

information on how you can identify them. Care should be taken in the management of your 

toadflax biocontrol program to ensure that all related native species are identified and monitored 

along with toadflaxes. 
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96 Chapter 4: Elements of a Toadax Biological Control Program

If you observe approved biocontrol agents feeding on and/or developing on nontarget species, 

the vegetation sampling procedures described above can be easily modified to monitor changes 

in density and/or cover of the nontarget species. Concurrently, you may wish to collect 

additional data, such as the number of agents observed on nontarget plants, the amount of 

foliar attack observed, or the presence of characteristic biocontrol agent damage. Collecting 

this data over subsequent years can help determine if there is a population level impact or if 

the nontarget feeding is temporary or of minor consequence to the nontarget species. Please be 

aware that there are many “look-alike” native insects that feed on related native plants. Correct 

identification by insect specialists is needed to confirm such records. 

If you observe approved biological control agents feeding on and/or developing on native 

species, collect samples and take them to a biocontrol specialist in your area. Alternatively, you 

may send the specialist the site data so he or she can survey the site for nontarget impacts. Be 

sure not to ascribe any damage you observe on native species to any specific species and thus 

bias the confirmation of attack and the identification of the species causing the attack. 

BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 5: An Integrated Toadax Management Program 99 

CHAPTER 5: AN INTEGRATED TOADFLAX MANAGEMENT PROGRAM 

Introduction 

Classical biological control has been applied to many invasive plant species, and there are several 

examples in which both single- and multiple-biocontrol agent introductions have successfully 

controlled the targeted weeds. At some locations, biological control can maintain toadflax 

densities below economically or ecologically significant levels, enabling land managers to live 

with the weed; however, it may take three to five years or more for biological control to reduce 

weed populations to such manageable levels. Furthermore, toadflaxes occur across a wide 

range of conditions. Some habitats are unsuitable to biocontrol agents, so biological control 

is not going to work against toadflaxes every time at every site. Depending on the infestation, 

integration with other weed control methods or resorting to other control measures entirely 

may be required to attain toadflax management objectives. A wide variety of successful weed 

control methods have been developed and may be useful for helping meet management goals 

for toadflaxes. The most successful long-term toadflax management efforts have a number of 

common features, including: 

• Education and Outreach 

• Inventory and Monitoring 

• Prevention 

• Weed Control Activities: A variety of toadflax control activities which are selected based on 

characteristics of the target infestation and planned in advance to use the most appropriate 

method or combination of methods at each site, including: 

○ Biological control 

○ Physical treatment 

○ Cultural practices 

○ Chemical treatment 

Programs that incorporate many of these activities are called Integrated Weed Management 

(IWM) programs, and they address several aspects of land management, not just weed control. 

Land managers or landowners engaged in IWM take the time to educate themselves and 

others about the threat invasive plants pose to the land. They get out on their land and look 

for potential threats, including toadflaxes. When an infestation is found, they map it and make 

plans to address it utilizing single or combined control methods most appropriate for their 

particular infestation. After initiating control activities, they monitor if the control efforts were 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

100 Chapter 5: An Integrated Toadax Management Program

successful. If re-treatment or additional treatments are necessary, these are applied in a timely 

manner with appropriate post-treatment monitoring to ensure that management objectives are 

being met. 

Integrated Weed Management programs undertaken on a landscape level over many years can at 

times prove logistically difficult, expensive, and time-consuming. The concept of Cooperative 

Weed Management Areas (CWMA) was created in western North America in order to erase 

jurisdictional boundaries and make a landscape approach to weed management more feasible 

and successful. CWMAs consist of federal, state and local land managers, as well as concerned 

private landowners, within a delineated area who join efforts against exotic plants, pooling 

and stretching limited resources and manpower for managing invasive species and protecting/ 

restoring habitat. Cooperation between neighboring CWMAs helps transfer knowledge and 

experience between heavily treated regions and places not yet as impacted by toadflaxes. 

Sharing successes and failures in toadflax management saves time and funding and reduces 

the incidence of negative impacts from management efforts, such as herbicide resistance. 

Numerous CWMAs exist throughout the western states of the USA and are excellent sources 

of information, experience, and resources for treating toadflax infestations using an IWM 

approach. 

The components of toadflax IWM are described individually below. Because the focus of this 

manual is the biological control of toadflaxes, the potential to integrate biocontrol with other 

weed control methods is described at the end of each control method’s section. Long-term 

management success is greatly improved when control methods are identified according to 

infested habitat type, land use, ownership, and available resources and then integrated when 

appropriate. 

Components of Successful Integrated Weed Management 

Programs to Manage Toadaxes 

Education & Outreach 

Education and outreach activities increase public 

awareness of noxious weeds, the problems they 

cause, their distribution, and ways to manage them 

(Figure 80). Ideally, education and outreach activities 

also foster cooperation and collaboration across land 

ownership boundaries to facilitate the development of a 

landscape-level weed management response. Education 

efforts should be an important component of any weed 

management plan, regardless of the target weed or weed 

control method employed. 

Figure 80. Dalmatian toadax education 

poster (University of Nevada, 

Cooperative Extension) 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 5: An Integrated Toadax Management Program 101 

Toadflax education and outreach should focus on conveying to the public: 

• the threat toadflaxes pose 

• how to identify toadflaxes (and their hybrids) in different stages 

• the importance of not utilizing/planting toadflaxes or their hybrids in any setting 

• ways in which they can help in toadflax management 

By educating land managers and landowners, recreationalists and the public about the threat 

of toadflaxes, enabling them to identify infestations, and enlisting them in mapping and 

management efforts, it becomes possible to cooperatively develop successful weed management 

responses at the landscape level. 

Inventory & Mapping 

Inventory and mapping are key elements of a successful weed management program. It is 

imperative to accurately characterize the size and extent of weed infestations before control 

activities are identified, prioritized, and implemented because the best treatment methods are 

often determined by the size and location of the infestation. Education and outreach activities 

that foster collaboration between adjacent landowners are particularly useful when developing 

landscape-level maps of weed infestations. Once land managers and landowners fully 

understand the threats toadflaxes pose to their land, they are often more willing to participate 

to ensure that their land is inventoried and accurate maps of toadflax are developed so the best 

control activities can be implemented. 

Toadflax infestations are often mapped by foot, vehicle, horse, or airplane using a global 

positioning system unit (GPS) and a geographical information system (GIS), though hard copy 

maps made by hand are suitable for some locations. An exciting recent development is the 

increasing use of free smartphone and tablet apps that make accurate, detailed, and versatile 

weed mapping available to anyone (e.g. the apps available from EDDMapS, see page 90 for 

more information). Inventory efforts should document the following for each infestation: 

location coordinates, boundaries, estimated density (number of stems of target weed per area, 

e.g. square meter or square yard), land usage, treatment history, disturbance history (e.g. 

fire, flooding), habitat type (wetland, upland, shrubland, grassland), and date. Photos of the 

infestation and a list of co-occurring species are also very useful. Documenting inventory and 

mapping efforts enables land managers to determine if all known toadflax infestations have 

been treated, and facilitates post-treatment monitoring. In turn, this allows land managers to 

judge the effectiveness of various treatment methods. See Chapter 4 for suggested techniques 

of monitoring infestations. 

Prevention 

Prevention activities focus on areas not currently infested by toadflaxes with the goal of 

keeping these areas weed-free. Though toadflaxes are already present throughout much of 

North America, there are many sites where they are absent or remain at low densities. Inventory 

efforts help identify the precise borders of these locations. Preventing the introduction and 

spread of toadflaxes to uninfested areas is more environmentally desirable and cost-effective 

than treating of large-scale infestations. 
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102 Chapter 5: An Integrated Toadax Management Program

Toadflaxes are spread by the movement of seed by humans and animals (livestock and wildlife), 

primarily along transportation corridors such as rivers, roads, recreation and game trails, and 

rail lines. Seeds can be caught on motorized equipment, mud on tires or clothing, hay, or 

animal fur. Because seeds ingested by animals often remain viable upon defecation, livestock, 

birds, elk, and deer grazing toadflax fruits in autumn is one of the primary modes of toadflax 

long distance seed dispersal. Limited seed dispersal of yellow toadflax may occur by wind, 

and both toadflaxes and their hybrids may be spread short distances locally by insects and 

rodents. Root fragments can also spread toadflaxes into uninfested areas. Preventing the spread 

of toadflaxes requires cooperation among all affected landowners and land managers. In areas 

where toadflaxes are not yet present, it is important to ensure that possible invasion avenues are 

identified and management actions taken to reduce the risk of spread. This includes minimizing 

soil disturbances and regularly monitoring uninfested sites to confirm that they have remained 

uninfested. 

Cultivation, soil erosion (especially following flooding events and prescribed or wildfire), road 

grading, recreational activities (e.g. riding dirt bikes or four wheelers), and overgrazing all 

weaken existing plant communities, decrease plant cover, and cause disturbance, conditions 

that favor toadflax establishment and persistence (Figure 81). Because such activities are also 

potential ways of spreading toadflax seeds, they should either be avoided or closely monitored 

in toadflax-prone areas. Where grazing does occur, proper livestock management (such as 

strategic timing and stocking rates) will allow grazed vegetation to recover and competitive 

plants to increase which, in turn, will help prevent the establishment of toadflaxes. If possible, 

livestock should be kept off weed-infested land when they are most likely to spread viable 

seeds (e.g. after seed formation). If it is not possible to avoid driving vehicles and machinery 

(e.g. logging, construction, or rangeland fire-fighting equipment) through toadflax infestations, 

it is crucial that a thorough cleaning take place before equipment leaves the contaminated area. 

Prevention and exclusion activities are typically paired 

with education efforts. Examples of exclusion efforts 

include weed-free forage programs, state and provincial 

seed laws, and mandatory equipment cleaning when 

leaving infested sites and before entering uninfested 

sites. 

EDRR 

An early detection and rapid response (EDRR) program 

is a specific protocol for tracking and responding to new 

infestations. It relies heavily on education and outreach 

activities to be effective. An EDRR program targets 

areas where toadflaxes may spread. It consists of three 

complementary activities: 1) educating land managers 

and the public on weed identification and mapping 

techniques, 2) enlisting their aid in immediate and 

thorough detection of the weed and 3) initiating rapid 

response eradication efforts at all verified locations of 

the weed. 

Figure 81. Dalmatian toadax growing 

in soil disturbed by railroad 

activities (Steve Dewey, Utah 

State University, bugwood.org) 
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Chapter 5: An Integrated Toadax Management Program 103 

Weed Control Activities 

Biological Control 

Biological control involves the use of living organisms, usually insects, mites, or pathogens, 

to control a weed infestation and regain the balance among coexisting plant species. Classical 

biological control focuses on the introduction of host specific natural enemies from the 

invasive weed’s native range. This method of toadflax management is the most economical 

and suitable control option for larger infestations (tens to thousands of acres), though some 

smaller infestations have shown great suppression by biocontrol agents. For small patches 

(less than 4 acres or 1.6 hectares) of new satellite (those growing outside of well-established) 

toadflax infestations, more aggressive control methods should be utilized (e.g. physical control 

or herbicides). Refer to Chapter 3 for detailed descriptions of the biological control agents 

currently approved for use against toadflaxes and Chapter 4 for how to implement a toadflax 

biological control program in your area. 

Physical Treatment 

Physical treatment utilizes hand pulling, mowing, or tilling to remove or disrupt the growth of 

weeds and is the oldest method of weed control. Physical methods have had variable success 

in controlling toadflaxes but are often labor-intensive and not suitable for the more rugged and 

inaccessible sites where toadflaxes have invaded. Due to toadflax’s ability to regenerate from 

severed root fragments, extreme care must be taken to ensure physical control methods are 

carried out under the appropriate conditions so that toadflax populations do not increase as a 

result of control efforts. Regardless of the physical method employed, it is imperative that all 

equipment used be thoroughly cleaned following use to prevent the spread of toadflax seeds or 

propagating root or stem fragments. 

Hand pulling 

Hand pulling can provide successful control of small toadflax infestations (under 1 acre or 

0.4 ha) if applied persistently. It is especially effective on young plants growing in sandy, 

moist, and/or loose soil (Figure 82). As plants age, or for plants growing in compacted soils, 

hand pulling can increase the size of the infestation due to seedling recruitment in the newly 

disturbed soil, and to regeneration from the severed roots of pulled plants. To account for this 

plant response, small populations of older toadflaxes individuals must be pulled several times a 

year and often for multiple years. Multiple hand-pulling sessions will also control new toadflax 

individuals sprouting later in the growing season from seeds lying dormant in the seed bank. 

It is important to remove as much of the toadflax root as possible, while minimizing soil 

disturbance. When toadflax plants are in flower or seed, cut off and bag all flowering stems 

prior to pulling. Otherwise, the jarring action of pulling may dislodge and distribute seeds at 

the site. All roots, stems, flowers and seeds should be securely bagged and taken to the trash 

or a transfer site to prevent possible toadflax vegetative growth or seed dispersal from pulled 

material. Re-seeding the open space resulting from toadflax removal with seeds of desirable 

vegetation can provide competition that will decrease successful toadflax seedling germination 

and establishment. 

Due to the destructive nature of hand pulling, this control method is not compatible with 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

104 Chapter 5: An Integrated Toadax Management Program

biological control. Hand pulling is most appropriate for small infestations where immediate 

eradication is feasible, while biological control is more appropriate for much larger, established 

infestations. One way to successfully combine these two methods is to release biological 

control agents in a large, main infestation while employing hand pulling to remove individual 

plants and to control small, satellite patches arising outside of the main toadflax infestation. 

Figure 82. Hand pulling Dalmatian toadax (Rachel 

Winston, MIA Consulting) 

Mowing 

Mowing toadflaxes may decrease seed production. Though this can decrease the rate of 

toadflax spread by seed, it does not alter the existing seedbank and does not kill toadflax 

plants. In many cases, mowing may exacerbate the problem by stimulating toadflax re-growth 

(and subsequent flowering) and reducing competition from surrounding vegetation. Multiple 

mowing events are necessary in order to truly decrease toadflax seed production. However, 

long-term mowing of yellow toadflax populations can result in toadflax plants growing shorter 

and successfully flowering and setting seed beneath the mower height (Figure 83a). Frequent 

mowing of toadflaxes is not feasible in either the crop or rangeland setting where toadflaxes are 

so problematic in North America, but it may provide control of toadflaxes along roadsides and 

rights-of-way. Alternatively, mowing can be used to remove excess plant litter and overgrowth, 

which will improve the effectiveness of herbicide applications on toadflax re-growth. When 

mowing is used as a form of toadflax control, it is important that mowing treatments occur 

after plants flower but before seed production, because mowing can facilitate seed dispersal. 

This can be especially difficult to time properly in populations where plants flower at different 

times. 

The destructive nature of mowing is damaging to the larvae of Brachypterolus pulicarius, 

Calophasia lunula, Mecinus spp., Rhinusa antirrhini, and R. neta, all of which utilize aboveground parts of toadflaxes. Mowing is more compatible with the root-galling weevil, Rhinusa 

linariae, as larvae and pupae can be found in galls in the roots of toadflax. Adults of all toadflax 

beetle species are susceptible to mowing while feeding on toadflax shoot tips, foliage, and 

flowers. 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 5: An Integrated Toadax Management Program 105 

Figure 83. Physical control of toadax a. mowed patch where yellow toadax plants have re-grown 

and successfully owered lower than the height of the mower (Hal Pearce, USDA FS); b. 

tilled eld (background) infested with Dalmatian toadax, with a few scattered Dalmatian 

toadax plants in the foreground (Sharlene E. Sing, USDA FS RMRS) 

Tilling 

Tilling can be an effective form of control for yellow and Dalmatian toadflax if it is repeated 

every 7-10 days throughout the growing season, and repeated for multiple growing seasons. A 

single cultivation event can make the toadflax problem worse (Figure 83b) because toadflaxes 

are capable of regenerating from root fragments as small as 0.4 inches long (1 cm). Repeated 

tilling is not compatible with agricultural practices in active croplands where yellow toadflax 

is frequently a problem. In general, cultivation is not practical or desirable in the wildlands 

and rangelands where toadflaxes are so problematic in North America. Where repeated tilling 

is feasible, toadflax control is enhanced when an herbicide treatment is used in conjunction 

with cultivation, particularly to control the spread and regeneration of toadflaxes from root 

fragments. Sowing competitive pasture species or crops and adding fertilizer may also help 

prevent re-infestation by toadflaxes. 

Because cultivation destroys above-ground growth and can slice toadflax roots into numerous 

fragments, this form of weed control is typically destructive to all established species of 

toadflax biocontrol agents. Repeated tilling is most applicable in a crop setting, where chronic 

disturbance and the need to attain immediate control make biological control fundamentally 

incompatible. 

Cultural Practices 

Cultural methods of weed control (including flooding, burning, grazing, and seeding with 

competitive species) can enhance the growth of desired vegetation, which in turn provide a 

barrier that slows the invasion of noxious weeds onto at-risk sites. Regardless of which method 

is used, all cultural control techniques are more successful when combined with other control 

methods. 

Flooding and Burning 

For toadflax management, flooding is typically not practical due to logistical challenges posed 

by the location and landscape scale of many toadflax infestations. Burning has also largely 

been dismissed as ineffective. While above-ground growth can be destroyed by prescribed or 

wildfires, the extensive root systems of toadflaxes survive even the hottest fires and readily re-
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106 Chapter 5: An Integrated Toadax Management Program

sprout viable shoots. Toadflax re-growth thrives 

and proliferates in the disturbed, nutrient-rich 

soil, especially if competition from other plant 

species is reduced or eliminated following the 

fire. While fire often exacerbates the problem, 

it has been used intentionally in some locations 

to burn off plant litter in order to make the resprouting toadflaxes more visible for applying 

herbicides (Figure 84). When prescribed fire kills 

off competing vegetation, it will only increase 

the toadflax problem, even with subsequent 

herbicide applications. Revegetation with 

desired vegetation is recommended wherever 

fire is utilized to aid in toadflax chemical control. 

High temperature fires destroy the larvae and 

potentially many adults of Brachypterolus 

pulicarius, Calophasia lunula, Mecinus spp., 

Rhinusa antirrhini, and R. neta, all of which 

utilize above-ground parts of toadflaxes. In fires where the roots of toadflaxes are not damaged, 

burning should not affect the larvae of Rhinusa linariae. 

Grazing 

Toadflaxes produce secondary compounds known to deter herbivory, which may make them 

initially less attractive for grazing. Horses, and grazing wildlife have been observed lightly browsing 

Dalmatian toadflax (Figure 85a), and cattle, domestic goats, and domestic sheep have been used 

successfully to suppress Dalmatian toadflax infestations (Figure 85b). Dalmatian toadflax provides 

adequate nutrition to livestock during targeted grazing; the animals feed on Dalmatian toadflax 

regularly and preferentially following a period of exposure. Grazing animals often avoid yellow 

toadflax, though deer and elk have been observed browsing flowering stems. Following prolonged 

exposure, cattle and sheep can be “trained” to graze yellow toadflax, which may help reduce seed 

production if animals are utilized short-term during flowering stages (Figure 85c); however, the 

effectiveness of using grazing to control yellow toadflax is largely unknown. The effect of grazing 

on hybrid toadflax has not been studied. 

Grazing can exacerbate toadflax infestations. Livestock grazing can stimulate re-growth in grazed 

stems, and animals spread toadflax seeds that usually remain viable, even after ingestion. Overgrazing 

infested pastures reduces toadflax competition and increases soil disturbance, enhancing the 

establishment and spread of toadflax. Consequently, utilizing livestock for toadflax management 

must be done with caution, close observation, and only under the right circumstances. 

Grazing the stems and flowers of toadflaxes would destroy populations of Brachypterolus 

pulicarius, Calophasia lunula, Mecinus spp., Rhinusa antirrhini, and R. neta. However, grazing 

that does not disturb the soil or roots of toadflaxes should not hinder the life cycle of the rootgalling weevil, Rhinusa linariae. Biological control may be more compatible with responsible 

bison grazing because the bison diet consists primarily of grasses and, in general, less than 5% forbs. 

Figure 84. Burning toadax with prescribed 

re (David Cappaert, Michigan State 

University, bugwood.org) 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 5: An Integrated Toadax Management Program 107 

Figure 85. Grazing toadaxes a. deer grazing Dalmatian toadax fruits; b. cattle grazing late-season 

Dalmatian toadax (a,b Sharlene E. Sing, USDA FS RMRS); c. cattle-grazed yellow toadax 

outside of exclusion cage and yellow toadax still growing within exclusion cage. Trampled 

area surrounding cage is a result of cattle utilizing the cage panels for rubbing/scratching 

(Jessica Richert, The Nature Conservancy) 

Seeding competitive species 

Yellow toadflax is an economically important weed in crops such as mint, canola, barley, 

wheat, and strawberries. In this setting, planting the affected crops at high densities, using 

high quality seed/transplants, and planting crop species or varieties well adapted to local 

environmental conditions are all helpful for reducing yellow toadflax infestations. Tilling and/ 

or applying selective herbicides and fertilizer to infested fields prior to planting enhances crop 

competitiveness and can increase yellow toadflax control. 

In natural settings where toadflaxes are established and then suppressed by one or more control 

methods, reinvasion by toadflaxes or other undesirable species is likely if the ecological niche 

they occupied remains unfilled. Successful long-term management requires taking active 

measures to enhance the establishment and maintenance of desirable competitive species to 

avoid reinvasions. 

Toadflax seedlings are sensitive to competition for light, moisture, and soil nutrients. Studies 

have shown that seeding with various exotic and native species can successfully reduce toadflax 

establishment while also proving beneficial to wildlife. The most suitable plant species to use 

for competition with toadflaxes depends on habitat, site conditions, climate, management goals, 

and future land use. Ideally, planted seeds should contain a mix of species, some of which 

should be quick to germinate and others to provide more long-term competition to toadflax 

seedlings. Utilizing ecologically equivalent species (those with root and growth patterns 

similar to toadflaxes) may provide the best competition. Inventorying nearby sites that are 

uninvaded by toadflaxes may provide insight into the best replacement species. Consult your 

local county extension agent or Natural Resource Conservation Service (NRCS) representative 

for additional help in determining the best alternatives in your area. Further suggestions for 

ecoregions throughout the United States may be found on the Native Seed Network website 

(please see Chapter 5 References for the URL). Likewise, the “links” section of the USDA 

PLANTS website offers numerous revegetation guideline manuals specific to different regions 

of both the United States and Canada. The USDA PLANTS site also provides access to a 

program and fact sheets that utilize soil, plant, and climate data to select plant species that 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

108 Chapter 5: An Integrated Toadax Management Program

are site-specifically adapted, suitable for the selected practice, and appropriate for the goals and 

objectives of the revegetation project. 

Control of toadflaxes prior to seeding more desirable species is important because established 

toadflax plants are highly competitive. Seeding of competitors should take place immediately 

following exposure of soil to maximize their competitive abilities (Figure 86). For example, 

seeding should occur in bare soil following burning or after young toadflax plants have been hand 

pulled or killed with herbicides. Because high populations of rodents can reduce the success of 

re-seeding, erecting a raptor perch/pole may discourage rodent habitation and help ensure seeded 

species successfully germinate and establish. 

Incorporating biocontrol agents with re-seeding has not been studied explicitly for toadflaxes, but 

could be difficult, primarily because the methods used to establish a productive stand of competitive 

species are not always compatible with the establishment and survival of biological control 

agents. Any method used to initially reduce toadflax stems and foliage to promote the growth of 

competitive species would hinder the survival of Brachypterolus pulicarius, Calophasia lunula, 

Eteobalea spp. Mecinus spp., Rhinusa 

antirrhini, and R. neta. Consequently, 

many successful revegetation programs 

establish competitive plant species first, 

using biological control agents after the 

seeded species have become established 

and toadflaxes begin to reappear. 

Alternatively, revegetation projects 

can target only a small portion of the 

infestation annually, leaving a reservoir of 

toadflax plants to support biocontrol agent 

populations. In some settings, it may be 

the biological control agents that open up 

the competing plant canopy, allowing for 

subsequent re-seeding to occur. 

Chemical Control 

Many herbicides are registered for use against toadflaxes growing in a variety of locations. 

Herbicide usage is most effective on small infestations, including newly established populations 

and recently established satellite patches arising from nearby older, larger toadflax infestations. 

If utilized appropriately, herbicides may also be useful on the leading edge of large, advancing 

toadflax infestations. 

Herbicides may be too costly to be of practical use in treating extensive infestations of toadflaxes 

and, similar to physical and cultural control methods, are also impractical in hard-to-access and 

environmentally sensitive areas. Repeated herbicide applications may be required over time as 

toadflax plants can re-sprout from their root system if not completely killed, and new toadflax 

plants may germinate from the seedbank. Potential nontarget damage to associated vegetation 

must also be considered when using herbicides. For these reasons, herbicides are best used as part 

of a larger, integrated weed management program that employs other weed control methods in 

areas where herbicides are less likely to be cost effective or the most appropriate control choice. 

Figure 86. Revegetation eorts following soil 

disturbance (Lassen Volcanic National Park) 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 5: An Integrated Toadax Management Program 109 

Herbicides are generally applied in one of two ways: spot or broadcast applications. Spot 

treatments are used for individual toadflax plants or small patches. In spot applications, an 

appropriate herbicide is applied to the foliage of target plants only, thus reducing nontarget 

effects (Figure 87a,b). Broadcast treatments spray an appropriate herbicide over an entire area 

to treat larger weed infestations. Broadcast treatments should be used with caution as many 

herbicides also impact plants that land managers may want to retain. If a broadcast treatment 

should kill all plants in a treated area, the bare soil remaining often allows the toadflaxes to 

reinvade from the seedbank, creating a larger infestation than was there originally. Selective 

herbicides are those that target selected species (e.g. broad-leafed forbs vs. grasses) while 

leaving other species virtually unharmed. Utilizing selective herbicides in spot treatments 

helps reduce the nontarget impacts of herbicide applications, and is the recommended approach 

for treating toadflax infestations with chemical control. The herbicide label should always be 

referenced to help determine the chance of nontarget species damage. 

a b 

Figure 87. Applying herbicides a. Dalmatian toadax (Sharlene E. Sing, USDA FS RMRS); b. yellow 

toadax (Hal Pearce, USDA FS) 

The optimal timing for herbicide application depends on site-specific variables including 

the stage of the toadflax plants and the climatic conditions present at the site. For example, 

chemical control of Dalmatian toadflax in California is most effective when treated plants 

receive adequate seasonal rainfall and are in the post-senescence or early rosette stage, as 

opposed to the early flowering stage for Great Plains and Intermountain West plants. Most 

herbicides currently registered for use against yellow toadflax work best when applied during 

flowering or in fall. For Dalmatian toadflax, treatments are most effective using picloram at full 

flower, and using chlorsulfuron in the spring or fall when applied to emerging rosettes (prior 

to bolting). The thick surfaces of leaves on Dalmatian toadflax hinder the uptake of herbicides, 

so adding a surfactant to the herbicide mix is highly recommended. Recent research has 

shown that a methylated seed oil/silicone blend surfactant works much better than the standard 

non-ionic surfactant. In general, yellow toadflax has been found less responsive to herbicide 

treatments than Dalmatian toadflax; higher application rates are often required when treating 

yellow toadflax. For both species, repeat applications and careful attention to the timing of 

application are required. The efficacy of herbicide compounds, application rates, and timing 

are not currently known for hybrid toadflax, though are likely to vary depending on the genetic 

composition of the population. 

Some of the most widely used herbicides to combat toadflaxes in North America include: 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

110 Chapter 5: An Integrated Toadax Management Program

• Chlorsulfuron application recommendations for Dalmatian toadflax vary depending on 

location; the majority state either bud-bloom stages or in fall when plants become dormant. 

The best success against yellow toadflax (up to 98% control for two years post-application) 

has been achieved when chlorsulfuron was applied during late summer or early fall when most 

of the shoots had already flowered so that adventitious root bud activity had begun. The highest 

rates of application are necessary in order to achieve the greatest success against both toadflax 

species, though these rates interfere with grazing restrictions on the label. Chlorsulfuron 

should be mixed with a surfactant to increase weed control results. A methylated seed oil/ 

silicone blend surfactant is recommended. This herbicide is selective against broadleaf 

species, but can also affect some grasses at certain application rates, so limiting its 

use should be considered when used in conjunction with some revegetation efforts. 

• Picloram has been applied more frequently than any other herbicide against Dalmatian or 

yellow toadflax, except where prohibited by proximity to water. It has proven effective 

against Dalmatian toadflax when applied during full flowering or in early fall. Picloram 

alone provides short-term control of yellow toadflax when applied during flowering or in 

fall. Because yellow toadflax can reportedly recover from single applications of picloram, 

repeated annual applications are recommended for three consecutive years to achieve 

lasting results. Control of yellow toadflax increases dramatically if picloram is combined 

with diflufenzopyr and dicamba. Picloram has a long soil residual period, which will 

reduce re-growth from Dalmatian and yellow toadflax roots or seedlings for 2-3 years 

post-application. Picloram is less useful in hot, sunny conditions or in sandy soil because 

it is degraded by sunlight and can leach below the root zone in sandy soils. This herbicide 

is safe to use over established grasses, however young monocots may be affected. 

It will kill desirable legume species, and may kill other desirable broadleaf plants. 

• Imazapic is reportedly effective against both Dalmatian and yellow toadflax, though one 

study found it be somewhat ineffective against Dalmatian toadflax. Imazapic gives the best 

results when applied (along with a surfactant) to Dalmatian and yellow toadflax in fall, after 

a hard frost. This herbicide is selective against broadleaf species, but can also target 

some grasses depending on application rates, so its use should be limited when used in 

conjunction with some revegetation efforts. In particular, cool-season grasses such as 

bluegrass and smooth brome are injured when imazapic is applied at high rates. Always 

follow label recommendations regarding re-planting intervals when using Imazapic. 

• Imazapyr is reportedly best applied to Dalmatian and yellow toadflax anytime plants are 

growing rapidly/actively. However, one study in California found excellent control was 

only achieved when imazapyr was applied in mid-fall to dormant plants. It is a nonselective herbicide and should only be used in spot treatments and in situations where 

loss of nontarget vegetation is acceptable. It is soil-active with a long residual activity, so 

is effective against preventing seedling germination. However, it can harm other plants 

rooted in the general area or even downhill and can interfere with revegetation efforts. 

• Dicamba should be applied to actively growing Dalmatian and yellow toadflax rosettes in 

spring; effectiveness decreases once plants bolt or are dormant. Dicamba alone is usually 

not very effective herbicide against toadflaxes because although it can kill above-ground 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 5: An Integrated Toadax Management Program 111 

growth, plants re-sprout from the roots, and repeated applications are required. However, 

there is some residual activity of dicamba that is useful against the seedbank. Dicamba is 

often mixed with other herbicides (especially picloram and diflufenzopyr) to increase weed 

control results. When mixed with diflufenzopyr, dicamba is accumulated in the plant and is 

more effective against the root system. Dicamba will likely kill desirable broadleaf species, 

including legumes.Alone, it does not kill grasses, sedges, cattails or other monocots (though 

increased effects may be observed when it is used in combination with diflufenzopyr). 

• 2,4-D can be applied to Dalmatian and yellow toadflax rosettes or bolting plants in 

spring in conjunction with other broadleaf herbicides to increase their efficacy or help 

provide short-term control at lower application rates. 2,4-D, alone, will not harm grasses, 

sedges, cattails, or other monocots. However, 2,4-D alone is not the most effective 

herbicide against toadflaxes as there is no soil activity, and though above-ground growth 

may be killed, plants will re-sprout from the roots and from the soil seedbank. Repeated 

applications are required. 2,4-D has a low cost, so is often combined with other herbicides 

that offer more complete and/or residual control, such as picloram or chlorsulfuron. 

• Glyphosate is typically applied to Dalmatian and yellow toadflax in spring during 

the actively growing rosette or bolting stages. It has had variable results against 

toadflaxes. It has no residual activity in the soil, and repeated applications are often 

required. It is a non-selective herbicide and will create bare ground. It should only 

be used in spot treatments and in situations where loss of nontarget vegetation is 

acceptable. Glyphosate use should be accompanied by revegetation of desirable species. 

• Aminocyclopyrachlor is a relatively new herbicide that can provide excellent control 

of toadflaxes (especially Dalmatian) when applied at the beginning of flowering. 

Aminocyclopyrachlor applied to post-flowering yellow toadflax showed no impact, likely 

due to the senescing plants not translocating the herbicide. Studies in Colorado have shown 

potential in the control of yellow toadflax, especially when combined with chlorsulfuron. 

Aminocyclopyrachlor is currently available for use in non-crop areas, and may have a 

range and pasture label in the near future. It is available as a stand-alone herbicide, and 

is also sold pre-mixed with both chlorsulfuron and metsulfuron methyl. Caution should 

be utilized with this compound as aminocyclopyrachlor can cause severe damage to 

nontarget plants, including trees, shrubs, many broadleaf species, and some grasses. 

When herbicides are used against toadflaxes, it is important that the applicator adhere to all label 

instructions to ensure the usage, surfactant requirement, application rate, application timing 

and location/site of herbicide application fall within label recommendations. Not all herbicides 

are registered for use against toadflaxes in all settings (including on or near water), or for use 

in each state of the USA and in Canada. Some herbicides are restricted use and can only be 

applied by a certified and licensed applicator, and then only under specific conditions. Herbicide 

treatments can vary widely depending upon geographic location, climatic conditions and rate 

of application. Please consult your local weed control authority, county agricultural extension 

agent, or forest invasive coordinator to learn which herbicides work best for toadflaxes control 

and when to apply them in your area. 

If land usage of treated areas includes grazing practices, consult the herbicide label for any 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

112 Chapter 5: An Integrated Toadax Management Program

grazing restrictions that might be applicable. 

Heavy herbicide use will reduce the toadflax stems, leaves, and flowers on which Brachypterolus 

pulicarius, Calophasia lunula, Mecinus spp., Rhinusa antirrhini, and R. neta rely, thus hindering 

establishment of these species. Herbicides which kill toadflax root systems in addition to 

above-ground growth will likewise hinder the establishment of Rhinusa linariae. One way to 

successfully combine these two methods is to release biological control agents in a large, main 

infestation while applying herbicides to control small, satellite patches surrounding the main 

toadflax infestation. 

The advantages and disadvantages of the most common toadflax control methods are 

summarized in Table 10. 

Use Herbicides Safely! 

Read the herbicide label, even if you have used the herbicide before. Follow all 

instructions on the label. 

Wear protective clothing and safety devices as recommended on the label. 

Bathe or shower after each herbicide application. 

Be cautious when you apply herbicides. Know your legal responsibility as an 

herbicide applicator. You may be liable for injury or damage resulting from 

herbicide use. 

Follow all storage and disposal instructions on the herbicide label. 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Chapter 5: An Integrated Toadax Management Program 113 

Table 10. Comparison of toadax management options. 

Control Method 

AdvAntAge 

disAdvAntAge CoMpAtibility with 

bioControl 

Biological Control 

Selective 

Measurable changes in weed densitiesmay take many years (eradication isnot the goal) Competition between Rhinusa antirrhini 

and Brachypterolus pulicarius preventsadditive impact in many locations. Heavyfeeding by Mecinus spp. suppresses flowering, which decreases the food source of R. 

antirrhini and B. pulicarius 

sustainable - agents generally do nothave to be reintroduced once established Some risk of undesirable effects on nontarget plants Public acceptance is generally higherthan with other weed control methods Permanent; cannot be undoneMost economical option for large infestations Not successful in all situations 

Physical Control(hand pulling) 

Useful for small infestations that mustbe quickly eradicated 

Must be repeated regularly due toconstant threat of re-establishmentfrom seedbank or plants re-growingfrom root fragments 

applicable only to very small infestationswhere biocontrol is not recommended.Hand pulling is not directly compatible with any biocontrol agent; however, biocontrol can be applied to large, main infestations while hand pulling can be usedon surrounding small, satellite populations

Reduces seed production Expensive and time intensive 

Physical Control(mowing) 

Repeated mowing may reduce seedproduction; leaf removal reducingphotosynthesis impedes root carbohydrate storage essential for plantpersistence and vigor 

May spread toadflaxes if done duringflowering or seeding; can spur compensatory growth; toadflax can setseed below blade 

Not compatible with Brachypterolus pulicarius, Calophasia lunula, Mecinus spp., Rhinusa antirrhini, and R. neta. Mowingis more compatible with larval and pupalstages of the root-galling weevil R. linaria. Expensive and time intensive; re- quires proper timing and equipment 

Physical Control(tilling) 

Can kill toadflax plants when done repeatedly over a single growing season 

Only applicable in limited cropsettings Not compatible with all established

toadflax biocontrol species. Tilling is only suitable in certain crop settings, where biocontrol is not recommended in general.

May spread toadflaxes if done infrequentlyExpensive and time intensive; requires proper timing and equipment 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

114 Chapter 5: An Integrated Toadax Management Program Table 10. Comparison of toadax management options. 

Control Method 

AdvAntAge 

disAdvAntAge CoMpAtibility with 

bioControl 

Cultural Control(grazing) 

Allows use of the land even withheavy toadflax infestations 

Cannot be used in many natural areassuch as national parks and wildernessareas 

Grazing toadflax stems and flowers woulddestroy Brachypterolus pulicarius, Calophasia lunula, Mecinus spp., Rhinusa antirrhini, and R. neta. Grazing may be

compatible with R. linariae if toadflaxroots are not trampled /damaged.Compatible with bison grazing. 

Non-selective; can exacerbate theproblem 

Can be used (under the right conditions) in combination with chemicalcontrol methods 

Can be expensiveKills only above-ground growth;toadflaxes can recover post grazing 

Cultural Control(re-seeding) 

Can be used to restore native species Expensive for large areas Compatible if biocontrol agents are

introduced after competitive species areestablished. Also compatible if re-seeding is done only on small sections of the infestation annually, leaving toadflax “refuges” for the biocontrol agents. In some settings,it is biocontrol that may make re-seedingfeasible. 

Can be self-perpetuating May be ineffective if existing toadflax stands are dense 

Chemical Control 

Fast acting 

Expensive for large areas; repeat applications and monitoring oftenrequired Herbicides are applicable only to small

infestations, which are unsuitable for biocontrol. Compatible when using biocontrolon a main infestation and herbicides onsurrounding small, satellite infestations.Herbicides that kill only above-groundgrowth may be safe for use with Rhinusa linariae, though they interfere with thefood source of Brachypterolus pulicarius, Calophasia lunula, Mecinus spp., Rhinusa antirrhini, and R. neta. 

Successful in reducing toadflax individuals in some settings, especially

in combinations with other controlmethods. 

May harm desirable, culturally sensitive or protected plant species 

If applied correctly and repeatedly, has the potential to eradicate somepopulations of toadflax 

Often ineffective on yellow toadflax; highly dependent on applying aneffective herbicide at the correct time in the growing season

Useful along transportation vectors(roads, trails, and occasionally waterways) 

Public resistance to chemical controlsRegulations or policies may prohibitus in some areas. 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Glossary 115

GLOSSARY

abdomen 

adventive 

alternate 

annual 

antenna (pl. antennae) 

aspirator 

basal

biennial

biological control 

biotype 

bolting

bract

capsule (from plant)

caterpillar

chrysalis

cocoon

community

complete metamorphosis 

compound eyes 

The last of the three insect body regions; usually containing the digestive and reproductive organs 

Species that arrived in the geographical area from elsewhere by any 

means, but is not self-sustaining and whose numbers are only increased 

through non-reproductive means, unlike a naturalized species 

Where leaves appear singly at stem nodes, on alternate side of the stem 

A plant that germinates, flowers , and dies all in the same year 

In arthropods, one of a pair of appendages on the head, normally many 

joined and of sensory function 

An apparatus used to suck insects into a collection container. The 

device can be simple (as in a mouth-aspirator) or mechanical (as in 

gasoline- or battery-powered vacuum aspirator) 

Located at the base of a plant or plant part 

A plant that flowers and dies between its first and second years and 

does not flower in its first year 

The reduction in abundance of a pest through intentional use of its 

natural enemies (predators, parasitoids, and pathogens) 

An informal subdivision of a species; generally, refers to a group of 

organisms that are morphologically identical to other individuals of a 

species but possess distinctive physiological characteristics (e.g., able 

to attack a normally resistant host, or not susceptible to a pesticide 

Plant stage at which the flower stalk begins to develop 

A small, leaf-like structure below a flower 

A pod or seed vessel made of two or more cells, which becomes dry 

and splits open when mature to release its seeds (see “head capsule” for 

capsule from insect) 

The larval stage of a moth or butterfly 

The pupal stage of a moth or butterfly 

A silk case that moth or butterfly larvae spin to contain the chrysalis 

A naturally-occurring group of different species of organisms that live 

together and interact as a more or less self-contained “unit” 

A life cycle with four distinct stages (egg, larva, pupa, adult) 

Paired eyes consisting of many facets, or ommatidia, in most adult 

Arthropoda 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

116 Glossary

coordinates A set of numbers used to specify a location 

defoliation The loss of foliage due to insect or fungal activity or the actions of 

abiotic factors (e.g. hailstorms) 

density Number of individuals per unit area 

dicot Plant with two seed leaves upon germination, including most common 

flowering species, excluding grasses, sedges, cattails, lilies and orchids 

dispersal The spread of animals and plants from any point; the redistribution of 

plant seeds, fungal spores, or insect eggs, larvae, and adults 

dissemination Dispersal. Can be applied to seeds or insects 

emergence (insect) Act of adult insect leaving the pupal exoskeleton, or leaving winter or 

summer dormancy 

elytron (pl. elytra) Hardened forewing of a beetle 

erect Grows upright and vertical as opposed to prostrate (spreading on the 

ground) 

exoskeleton Hard, external skeleton of the body of an insect 

exotic Not native 

field insectary An area where host plants or animals are abundant and biological 

control agents are released and propagated with or without additional 

human manipulation 

flower beetles Small beetles in the family Kateretidae, the adults and larvae of which 

consume flowers and/or seeds of host plants 

forb Herbaceous plant (does not have solid woody stems) 

frass Plant fragments, usually mixed with excrement, deposited by feeding 

insects 

gall A plant tumor; a localized proliferation of abnormal plant tissue that is 

induced by an insect, nematode, fungus or other organism and usually 

exhibits a characteristic shape and color; gall-making insects usually 

live and feed within the gall 

genus (pl. genera) A taxonomic category ranking below family and above species and 

consisting of a group of species exhibiting similar characteristics. The 

genus name is followed by a Latin adjective or epithet to form the 

name of a species 

GPS Global Positioning System; a space-based navigational system providing location and time information by using four or more satellites 

grub A so thick-bodied, C-shaped beetle larva 

head Insect segment with the mouth parts, antennae, and eyes 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Glossary 117

head capsule Hardened covering of the head of an immature insect 

herbivory Feeding on plants 

host The plant or animal on which an organism feeds; the organism utilized 

by a parasitoid; a plant or animal susceptible to attack by a pathogen 

host specificity The highly-evolved, often obligatory association between an insect and 

its host (i.e. weed). A highly host-specific insect feeds only on its host 

and on no other species 

hybrid The offspring of two parent of different species 

inflorescence The flowering part of the plant 

instar The phase of an insect’s nymphal or larval development between molts 

larva (pl. larvae) Immature insect stage between the egg and pupa (examples include 

grubs, caterpillars and maggots) 

lateral root Roots that extend horizontally from the primary root and serve to anchor the plant securely in the soil 

litter Dead plant material, such as leaves, bark, needles, twigs, that has fallen 

to the ground 

margin (of leaf) The edge of a leaf. Margins typically fall within a handful of categories 

and are useful in plant identification 

membranous Thin and transparent 

metabolic sink Any living cell, tissue, organ, or structure (e.g. gall) that is a storage 

depot of a metabolite 

molting Process of insect development 

monocot Plant with only one seed leaf upon germination, including grasses, 

sedges. cattails, lilies, and orchids 

monoculture An area vegetated by a single plant species 

NAD 83 North American Datum, the official datum used for the UTM geographic coordinate system in North America 

nectar A sugar-containing secretion produced by plants, usually in flowers, 

that often attracts insect pollinators 

node Part of the stem of a plant from which a leaf, branch or root grows 

nontarget effect When control efforts affect a species other than the species they were 

enacted to control (can be positive or negative) 

noxious weed A weed whose control is mandated, and whose movement is regulated 

by federal or state law 

oviposit To lay or deposit eggs 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

118 Glossary

perennial 

petiole 

plant cover 

pupa (pl. pupae v. pupate) 

qualitative 

quantitative 

rhizome 

root crown 

rosette 

senescence 

semi-gall 

snout 

species 

surfactant 

synchrony 

thorax 

transect 

UTM 

vegetative reproduction 

viability 

A plant that lives for more than two years 

Leaf stalk that attaches it to a plant stem 

The portion of the vegetative canopy in a fixed area attributable to an 

individual or a single plant species 

Non-feeding, inactive insect stage between larva and adult 

Measurement of descriptive elements (e.g. age class, distribution) 

Measurement of quantity; the number or amount (e.g. seeds per capitulum) 

A modified stem of a plant that grows horizontally underground, often 

sending out roots and shoots from its nodes 

Part of a root system from which a stem arises 

A compact, circular, and normally basal cluster of leaves 

Final stage in a plant’s life cycle when seeds are produced and plants 

die back 

Plant tissue produced as an irritation response to the presence of 

egg-laying fluids, eggs, larvae, or larval frass. Different from true galls, 

they appear externally to be smaller swellings on plant stems 

The prolongation of the head of a weevil 

A fundamental category of taxonomic classification, ranking below 

a genus or subgenus and consisting of related organisms capable of 

interbreeding 

Often applied with an herbicide mix to help bring the herbicide into 

closer contact with the leaf surface in order to aid absorption 

The classification of organisms in an ordered system that indicates 

natural relationships. The science, laws, or principles of classification; 

systematics 

Body region of an insect behind the head and abdomen, bearing the 

legs and wings 

A straight line of varying length along which plants are periodically 

sampled individually or in quadrants 

Universal Transverse Mercator, a grid-based geographic coordinate 

system 

Reproduction in plants other than by seeds, such as from rhizomes, 

stolons, and from nodes on lateral, often creeping roots 

The proportion of propagules (e.g. seeds) that are alive and can germinate 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Glossary 119

weevil A type of plant eating beetle, the adults having distinct snouts of variable lengths 

WGS 84 The World Geodetic System, a datum for latitude/longitude geographic 

coordinate systems 
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Nadeau, L.B., M.R.T Dale, and J.R. King. 1991. The development of spatial pattern in shoots 

of Linaria vulgaris (Scrophulariaceae) growing on fallow land or in a barley crop. 

Canadian Journal of Botany 69: 2539–2544. 
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Nadeau, L.B., J.R. King, and K.N. Harker. 1992. Comparison of growth of seedlings and 

plants grown from root pieces of yellow toadflax (Linaria vulgaris). Weed Science 

40:43–47. 

Native Seed Network. http://www.nativeseednetwork.org. Accessed 22 August 2015. 

Olson, B and K. Launchbaugh. 2006. Managing herbaceous broadleaf weeds with targeted 

grazing. Pp 58–67 In: K.L. Launchbaugh (Ed). Targeted Grazing: A Natural Approach 

to Vegetation Management and Landscape Enhancement. American Sheep Industry 

Association. Cottrell Printing, Centennial CO. 

Pacific Northwest Weed Management Handbook. 2014. Compiled by E. Peachey, D. Ball, R. 

Parker, J.P. Yenish, T.W. Miller, D.W. Morishita, and P.J.S. Hutchinson. Oregon State 

University Agricultural, Corvallis, OR. 451 pp. http://pnwhandbooks.org/weed/ 

Rose, K.K., T.D. Whitson, and D.W. Koch. 1999. The competitive effects of five cool-season 

grasses on Dalmatian toadflax (Linaria genistifolia ssp. dalmatica). Proceedings of the 

Western Society of Weed Science 52:64–67. 

Sing, S.E. and R.K.D. Peterson. 2011. Assessing environmental risks for established invasive 

weeds: Dalmatian (Linaria dalmatica) and yellow (L. vulgaris) toadflax in North 

America. International Journal of Environmental Research and Public Health 8:2828– 

2853. 

USDA, NRCS. 2015. The PLANTS Database (http://plants.usda.gov, 15 August 2015). 

National Plant Data Center, Baton Rouge, LA 70874-4490 USA. 

VanBebber, R. 2003. CWMA Cookbook: A Recipe for Success. Idaho State Department of 

Agriculture, Boise, ID. 22 pp. 

Zilke, S. and R.T. Coupland. 1954. The effect of one cultivation on the density of toadflax 

(Linaria vulgaris Hill). Research Report of the National Weed Committee, Western 

Section. p. 107. 

Zouhar, K. 2003. Linaria spp. In: Fire Effects Information System, [Online]. U.S. Department 

of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences 

Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [15 August 

2015]. 

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Appendices 129

APPENDICES

APPENDIX I: TROUBLESHOOTING GUIDE: WHEN THINGS GO WRONG 

Problem Probable Cause solution 

Biological control 

agents unhealthy or 

dead when received 

Physical damage to agents in 

transport 

Provide adequate packing material to minimize movement of 

containers and ice packs 

Drowning 

Do not put water in containers during transport; prevent accumulation of excess moisture; too much plant material causes 

condensation 

Excess or prolonged heat or cold Keep containers cool at all times; use coolers and ice packs; avoid 

exposure to direct sunlight while in transit 

Starvation Put toadflaxes foliage (no flowers, seeds or roots) in containers; 

minimize time agents are in containers 

Release delay 

Transport or ship agents immediately after collection 

Release agents at new site immediately upon arrival or receipt of 

agent 

Parasitism and/or disease Check source agents. Ensure the insect population is disease-free 

when collecting or receiving shipment 

Reproductive problems 

Agents past reproductive stage Collect at peak activity (i. e. insects are mating and ovipositing) 

Sex ratio: not enough males or 

females 

Collect at peak activity; observing mating among target agents 

before collecting; males often emerge earlier than females 

Agents not synchronized with 

the toadflax growth stage 

Biological control agents require the weed to be at specific growth 

stage for optimal oviposition; collect agents from sites with plants 

in similar stages. 

Few biological control 

agents collected 

Collection at wrong time Refer to Table 8 for collection time and technique 

Collection technique Biological control agents can be killed/damaged during sweeping 

or aspirating so sweep lightly; avoid debris 

Conditions at the time of collection wrong Refer to Chapter 4 section “Collecting Toadflax Biological Control Agents” for guidelines on desirable weather conditions 

Population insufficient Only collect from well established populations 

Agents not found after 

release 

Site is unsuitable or too small Refer to Chapter 4 section “selecting Biological Control Agent 

Release Sites” 

Not enough agents released Release at least 200 adults of the toadflax beetle species and at 

least 100 Calophasia lunula 

Pesticide use/mowing in area Select sites where land usage and management practices will not 

interfere with biological control agent life cycles 

Released on wrong species Ensure toadflaxes and the correct biological control agent are used 

Released at wrong time Release only during the correct plant stage and in the cool hours 

of the day. Refer to Table 8 for guidelines 

Agents not well adapted to 

conditions 

Release field-collected biocontrol agents from local sources 

wherever possible rather than greenhouse-reared adults or insects 

collected from distant locations 

Ants or other predators preyed 

upon biocontrol agents 

Release only at sites with no obvious ant mound or high insect 

predator populations (e. g. mice, voles) 

Cannot locate release 

site 

Location marker not obvious Use bright-colored wooden, metal or plastic stake 

Site destroyed Communicate with all direct and neighboring land users 

Map poorly/incorrectly drawn Check map; redraw with more detail or add landmarks; GPS 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

130 Appendices

APPENDIX II: SAMPLE BIOLOGICAL CONTROL AGENT RELEASE FORM 

Released By:_________________________ Release Date:___/___/___ State: _______ County:________ 

(mm dd yy) 

SITE CHARACTERISTICS 

Site Name:_______________________ Size of Infestation (acres):______ Estimated % Weed Cover:_____________________ 

Est. Weed Height (cm): _______ Est. Weed Density (# per meter sq.): _______ Dominant Plant:________________________ 

Distribution of Weed: Isolated_____ Scattered_____ Sc-Patchy_____ Patchy_____ Continuous_____ Linear_____ 

Phenology: Seedling % ____ Rosette % ____ Bolt % ____ Bud % ____ Flowering % ____ Seed % ____ Dormant % ____ 

Vegetation Type (check): Estimate % Cover: 

Grassland Tree _______________ 

Pasture Shrub _______________ 

Dry Meadow Forb _______________ 

Moist Meadow Grass _______________ 

Shrubland Steppe Litter _______________ 

Conifer Forest Bare Ground ___________ 

Rock _________________ 

Soil Texture: (check) Sand___ Silt___ Clay___ Gravel___ Loam___ 

Biocontrol Agent:_________________________________ # Released:_____________ 

Source of Agents:_________________________________________________ Date Collected:____/____/____ 

(mm dd yy) 

Life Stage (circle): Larvae Adults 

Land Ownership (circle): Private County State USFS BLM COE BOR BIA/Tribe TNC Other (specify) ________________ 

Legal: T_____ R_____ Sec_____ Q_____ Lat: Deg____Min____Sec______ Long: Deg___Min_____Sec_____ 

UTM: UTM Datum Zone: _ _ UTM Year: _ _ _ _ UTM Easting: _ _ _ _ _ _ _ _ UTM Northing: _ _ _ _ _ _ _ _ 

ENVIRONMENT 

Temperature (°F):________ Wind: Calm, Light, Moderate, Strong, Gusty Wind Direction: N S E W

Weather (circle): Clear Ptly Cloudy Cloudy Rain Snow Release Time:_____________ AM/PM

Site Aspect (circle): N, NE, E, SE, S, SW, W, NW Elevation:_________________________

Site Slope: Flat (0-10%) _______ Gentle (10-30%) _______ Moderate (30-60%) _______ Steep (>60%) _______

Topographic Position (circle): Valley Bottom Terrace Lower Slope Mid/Upper Slope Crest

Disturbance: (check all that apply, circle most prevalent) Cultivation ___ Fire ___ Flood ___ Grazing ___ Logging ____ 

Roads____ Mining ____ Recreation ____ 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Appendices

APPENDIX II: SAMPLE BIOLOGICAL CONTROL AGENT RELEASE FORM (SIDE 2) 

CONTACT PERSON: LEGAL LANDOWNER: 

Name: _____________________________________ Name:________________________________________ 

Address:____________________________________ Address: ______________________________________ 

City: _______________________________________ City: _________________________________________ 

State: ______________________________________ State: ________________________________________ 

Phone: _____ - ______ - ___________ Phone: _____ - ______ - ___________ 

e-mail: _____________________________________ e-mail: _______________________________________ 

Site 

Road	Map	to	Site

Site and Vegetation	Map

Comments: 

131
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Appendices

APPENDIX III: STANDARDIZED IMPACT MONITORING PROTOCOL (SIMP) 

Please see the following site for more information and downloadable forms: 

http://www.agri.idaho.gov/AGRI/Categories/PlantsInsects/NoxiousWeeds/Bio_Control.php

132
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Appendices 133

APPENDIX III: STANDARDIZED IMPACT MONITORING PROTOCOL (SIMP) (CONT.)
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

134 Appendices

APPENDIX III: STANDARDIZED IMPACT MONITORING PROTOCOL (SIMP) (CONT.)
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Appendices 135

APPENDIX III: STANDARDIZED IMPACT MONITORING PROTOCOL (SIMP) (CONT.)
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

136 Appendices

---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

____________________________________________________________________________________________________ 

________________________________________________________________________________________________________________ 

____________________________________________________________________________________________________ 

____________________________________________________________________________________________________ 

____________________________________________________________________________________________________ 

____________________________________________________________________________________________________ 

____________________________________________________________________________________________________ 

____________________________________________________________________________________________________ 

APPENDIX IV: GENERAL TOADFLAX BIOLOGICAL CONTROL AGENT MONITORING FORM 

SITE: _______________________________ STATE: ______________ DATE: _________ _________ _______ 

year month day 

Last name: _______________________________________ First name: _______________________________________ 

GPS: Lat N _____°___________' Long W_____°___________' Elevation: ________________________ ft m 

UTM: UTM Datum Zone: _ _ UTM Year: _ _ _ _ UTM Easting: _ _ _ _ _ _ _ _ UTM Northing: _ _ _ _ _ _ _ _ 

TIME: ___________ TEMPERATURE: ____________ WEATHER: __________________________________ 

1. Counting Biocontrol Agents This method is used to count adults of the flower-feeding beetle and the stem-mining 

weevil, and caterpillars of the defoliating moth. 

What to do For flower-feeding beetle: Count for 10 minutes

For each agent: For stem-mining weevil: Count for 5 minutes

For the defoliating moth: Count for 15 minutes

Number of agents observed 

 No agents observed 

 One agent observed 

 2-10 agents observed 

 10-50 agents observed 

 50-100 agents observed 

 >100 agents observed 

Agent feeding damage 

 No agent feeding observed 

 Occasional, scattered feeding damage observed 

 Conspicuous, widespread feeding damage observed 

2. Sweep-net or tray sampling This method is used for the seed-feeding weevils and the root-galling weevil. 

What to do For sweep net: Sweep plants 5 times; then count beetles 

for each sample: For tray sample: Tap plant 10 times to knock beetles onto a tray; then count 

Sample Weevils Sample Weevils Sample Weevils Sample Weevils 

1 6 11 16 

2 7 12 17 

3 8 13 18 

4 9 14 19 

5 10 15 20 

Total number of weevils collected:___________ 

Notes: _________________________________________________________________________________________________________ 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Appendices 137

APPENDIX IV: INSTRUCTIONS FOR GENERAL TOADFLAX BIOLOGICAL CONTROL AGENT 

MONITORING FORM 

Materials needed: stopwatch, sweep net, monitoring form, pencils, clipboard, camera, and GPS unit to record site location. 

General: The purpose of this monitoring activity is to estimate the abundance of toadflax biocontrol agents at your 

monitoring site. Conduct the monitoring when the biocontrol agents are at their peak. 

1) Site information: Fill out the site information at the top of the form. 

2) Insect counting: To estimate the density of biocontrol agents, you need to count them. Carefully approach the site and 

avoid disturbing the vegetation. Adults often drop from the vegetation once you touch stems (or even as you approach the 

quadrat). 

Timed Counting: Schedule monitoring to coincide with the adult stage of the biocontrol agent that you are sampling (or 

caterpillars of Calophasia). Randomly walk at a steady pace within the observation area, staying within 32 yd (30 m) of the 

release point. Accuracy is increased if you avoid backtracking over the same area because both beetles and caterpillars are 

easily brushed off or fall from toadflax. Beginning at the release point marker, count all the agents you see, concentrating on 

the top portions of the plants. Count the insects for five, 10, or 15 minutes, as appropriate, and record the number seen. 

Sweep net sampling: Using a sturdy canvas net, sweep the upper 3 in (10 cm) of the plant along transects 64 ft (20 m) long. 

Sweeping lower will give you lots of broken plant parts, but will not necessarily yield any more beetles. Make 20 samples of 

five sweeps each, sweeping relatively gently through the upper parts of the toadflax plants. Open the net after the five 

sweeps, count any biocontrol insects collected, then either release the captured insects, or place them in alcohol-filled vials for 

identity confirmation. You may also empty your sweep net into a white tray for immediate counting, or dump the tray 

contents into a large plastic cup that you can cover for later counting. The 20 samples can be taken randomly through the 

toadflax infestation, or by radiating in a straight line away from the release point along each cardinal direction (N, S, E, W). 

For the latter, do five to seven, five-sweep samples at regular intervals (e.g. 10-16 ft (3-5 m) apart) depending on the size of 

the toadflax patch. 

Tray sampling: This method is particularly useful when monitoring low to medium population densities of biocontrol beetles. 

Use a white or similarly light-colored plastic tray, pan, or other flat receptacle with sides. The tray should be rectangular or 

square (for ease of tipping collected insects into specimen vials or other containers), and 12-18 in (30-46 cm) on the longest 

side. Take 20 samples at each release location. For each sample, gently hold one toadflax stem or a handful of toadflax stems 

and shake or tap the upper stems 10 times over the collecting tray. This should dislodge at least some of the adults present; 

they can then be easily counted on the tray and released. Twenty to thirty samples may be taken randomly throughout the 

toadflax infestation, or you may collect tray samples radiating away from the release point along each cardinal direction (N, S, 

E, W). For the latter, do five to seven ‘beating’ samples at regular intervals (e.g., 10-16 ft (3-5 m) apart), depending on the 

size of the toadflax patch. 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

138 Appendices

______________________________________________________________________________________ 

APPENDIX V: TOADFLAX QUALITATIVE MONITORING FORM 

SITE: _______________________________ STATE: ______________ DATE: _________ _________ _______ 

year month day 

Last name: _______________________________________ First name: _______________________________________

GPS: Lat N _____°___________' Long W_____°___________'

UTM: UTM Datum Zone: _ _ UTM Year: _ _ _ _ UTM Easting: _ _ _ _ _ _ _ _ UTM Northing:________

TIME: ___________ TEMPERATURE: ____________ WEATHER: __________________________________ 

Biocontrol Insect: _____________________________ Year of release: _____________________ 

Toadflax Species (circle): Dalmatian yellow 

Cover class estimate by plant category 

0% 1-5% 6-25% 26-50% 51-75% 76-95% 96-100% 

Toadflax 

Grasses 

Forbs 

Shrubs 

Trees 

Dominant plant species on site: 

Other noxious weeds: 

Estimate toadflax density class (ücheck one) 

Flowering plants/m2 Toadflax distribution 

0 Isolated 

1-25 Scattered 

26-50 Scattered-Patchy 

50-75 Patchy 

>75 Continuous 

Toadflax phenology class 

Toadflax Stage Estimated percent 

Seedling 

Rosette 

Bolting 

Flowering 

Senescent 

Comments/Observations ________________________________________________________________ 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Appendices 139

___________________________________________________________________________________________ 

___________________________________________________________________________________________ 

___________________________________________________________________________________________ 

___________________________________________________________________________________________ 

APPENDIX VI: TOADFLAX QUANTITATIVE MONITORING FORM 

SITE: _______________________________ STATE: ______________ DATE: _________ _________ _______ 

year month day 

Last name: _______________________________________ First name: _______________________________________

GPS: N _____°___________' W _____°___________' Elevation: __________________________ ft m

UTM: UTM Datum Zone: _ _ UTM Year: _ _ _ _ UTM Easting: _ _ _ _ _ _ _ _ UTM Northing:________

TIME: ___________ TEMPERATURE: ____________ WEATHER: __________________________________ 

Chart A: 

Cover Class 

Class % Cover Class % Cover Class % Cover % Cover Class 

0 0 2 6-25 % 4 51-75 % 6 95-100 % 

1 1-5 % 3 26-50 % 5 76-95 % 

Quad 

# Toadflax Stems Cover Class 

(use Chart A) 

# 

flowering 

stems 

# nonflowering 

stems 

Height (cm) of 4 tallest 

stems 

Toadflax Grass Forbs Shrubs Litter Bare 

ground 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

20 

Notes: ___________________________________________________________________________________________________ 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

140 Appendices

___________________________________________________________________________________________ 

__________________________________________________________________________________________________________ 

___________________________________________________________________________________________ 

___________________________________________________________________________________________ 

___________________________________________________________________________________________ 

___________________________________________________________________________________________ 

___________________________________________________________________________________________ 

___________________________________________________________________________________________ 

APPENDIX VI: TOADFLAX QUANTITATIVE MONITORING FORM (SIDE 2)

Quad 

# Toadflax Stems Cover Class 

(use Chart A) 

# 

flowering 

stems 

# nonflowering 

stems 

Height (cm) of 4 tallest 

stems 

Toadflax Grass Forbs Shrubs Litter Bare 

ground 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

31 

32 

33 

34 

35 

36 

37 

38 

39 

40 

Notes: ___________________________________________________________________________________________________ 
BIOLOGY AND BIOLOGICAL CONTROL OF DALMATIAN AND YELLOW TOADFLAX

Appendices 141

INSTRUCTIONS FOR APPENDIX VI: TOADFLAX QUANTITATIVE MONITORING FORM 

Materials needed: 1.1 yd (1 m) measuring stick, 3.5 ft2 (0.1 m2

) quadrat frame, data sheets, pencils, clipboard, 

camera, and GPS unit to relocate quadrats. 

General: The purpose of this activity is to estimate the abundance of other vegetation in the community, and to 

record measurements of toadflax plant attributes. Monitoring is easier with two people, one to make the 

observations and the other to record data. 

1) Site information: Fill out the site information at the top of the form. 

2) Locate the transect and position the quadrat: After you have completed the insect counts, locate the 

transect using the GPS coordinates and the permanent marker. 

3) Position the quadrat frame: Position the quadrat frame along the transect, as close to the ground as possible, 

carefully positioning the quadrat frame along that transect line. Gently arrange vegetation so that plant parts are 

either within or outside, rather than underneath, the frame, but be sure not to damage the plants. The quadrat 

should be in the same location as the previous year’s quadrat. 

4) Count stems: Count the number of toadflax stems, beginning at one corner of the quadrat and working 

systematically across the quadrat. Count the number of flowering and non-flowering stems. 

5) Measure stems: Select the four tallest toadflax stems in each quadrat (if there are fewer than four 

stems/quadrat, measure all that are present). Measure the stem height to the closest cm. 

6) Estimate percent cover: Standing over the frame, estimate how much of the quadrat is covered by toadflax. 

Then estimate the percent cover of grasses, forbs, shrubs, plant litter, and bare ground. Use cover estimates in 

Chart A to estimate percent cover class. 

7) Other observations: Record any general observations or useful information such as disturbances, grazing, fire, 

etc., for the sample quadrat or the site in general.