Verticillium nonalfalfae

a promising, naturally occurring

biological herbicide to control

TREE OF HEAVEN

(AILANTHUS ALTISSIMA)

Rachel K. Brooks1, Raghavan Charudattan2, Donald D. 

Davis3, Matt T. Kasson4, Scott Salom5, 

Anton Baudoin1, Richard C. Reardon6

1

School of Plant and Environmental Sciences, Virginia Tech, Blacksburg, VA 2

BioProdex, Inc., Gainesville, FL 3

Dept. Plant Pathology and Env. Microbiology, Penn State, University Park, PA

4

Div. Plant and Soil Sciences, West Virginia University, Morgantown, WV 5

Dept. Entomology, Virginia Tech, Blacksburg, VA 5

FHAAST (retired), USDA Forest Service, Morgantown, WV

Forest Health Assessment and 

Applied Sciences Team

FHAAST-2019-03

March 2020
The Forest Health 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. 

FHTET became Forest Health Assessment and Applied Sciences Team 

(FHAAST) in 2016. This booklet was published by FHAAST as part of the 

technology transfer series.

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

This publication is available online at: 

https://www.fs.fed.us/foresthealth/technology/pdfs/FHAAST-2019-03_

Verticillium_nonalfalfae.pdf

https://bugwoodcloud.org/resource/pdf/verticilliumwilt.pdf

For additional copies of this publication, contact: 

Denise Binion FHAAST, USDA Forest Service, 180 Canfield Street, 

Morgantown, WV 26505; 304.285.1552; denise.binion@usda.gov

ACKNOWLEDGMENTS

This booklet was created as a compilation of the various works 

of the authors. In addition, we wish to thank Kristen Wickert (West 

Virginia University) and Joanne Rebbeck (Forest Service Northern Research 

Station, retired) for their assistance with this publication. We also extend 

our gratitude to Richard Reardon (FHAAST) for producing this booklet and 

to Rachel Winston (MIA Consulting) for designing the layout.

Cover images: (clockwise from top left) healthy TOH stand, diseased 

TOH stand, diseased TOH tree, healthy TOH tree (Photos: both stands by 

The Pennsylvania State University; Rachel K. Brooks, Virginia Tech; Chuck 

Bargeron, University of Georgia, Bugwood.org)
1

INTRODUCTION

Tree of heaven (TOH; Ailanthus altissima (Mill.) Swingle, 

Simaroubaceae) is native to eastern China. This deciduous 

hardwood tree was first introduced from England to the U.S. in 1784 

to a garden in Pennsylvania, and then several more times directly 

from China, including to Rhode Island in 1804 and to California by 

Chinese immigrants in the mid-1800s. TOH now occurs across the 

U.S. (Fig. 1) and is reportedly invasive in over 44 U.S. states. 

Figure 1. TOH distribution in the U.S. (Credit: EDDMapS, http://www.eddmaps.org/

accessed 11 February 2020)

TOH invades forests, rights-of-ways, 

urban areas, and agricultural lands

TOH displaces native vegetation 

important for wildlife habitat, 

timber production, recreation, and 

biodiversity

TOH roots produce allelopathic 

compounds that may reduce the 

establishment of other plants 

TOH is the preferred host of other 

invasive pests including the spotted 

lanternfly, Lycorma delicatula (White) 

(Fig. 2), and the brown marmorated 

stink bug, Halyomorpha halys Stål

TOH can cause allergic reactions (via 

pollen and direct contact) in humans 

TOH is also called Ailanthus, Chinese 

sumac, varnish tree, stink tree, and 

paradise tree

Figure 2. Spotted lanternfly 

colony on TOH (Photo: Rachel 

K. Brooks, Virginia Tech)
2

BIOLOGY & LIFE CYCLE

TOH is fast-growing with an extensive root system 

and prolific seed production. Mature trees can have a 

diameter up to 6 ft (1.8 m), reach up to 65 ft (20 m) tall, 

and can live for over 100 years. TOH tolerates a wide 

range of growing conditions, including air pollution 

and low quality soils, and is often found thriving in 

areas with high levels of disturbance. Once established, 

it is among the fastest growing trees in North America, 

often growing up to 6 ft (1.8 m) during its first year.

Seed production can begin within as little as 5 years (Fig. 

3a). Flowers are first observed on TOH in late spring to 

early summer (Fig. 3b). A single tree may produce up 

to 1 million seeds per year and over 50 million seeds 

during its lifetime. Seeds are readily spread by wind 

and water. Unlike some other species, TOH seeds can 

germinate immediately upon contact with the soil and 

can also remain viable for over 5 years. The leaves are 

deciduous, falling from the tree in autumn and winter. 

New leaves emerge in late spring. 

TOH also reproduces clonally through its suckering root 

system (Fig. 3c). Sprouts arise from the roots, root crown, 

and bole and typically grow much faster than seedlings 

(up to 10 ft [3 m] per year) because an extensive root 

system is already established. These develop into new 

plants and can quickly create large TOH monocultures.

a b c

Figure 3. TOH (a) tree, (b) flower clusters, and (c) suckers (Photos: a,c. Robert 

Vidéki, Doronicum Kft., Bugwood.org; b. H. Zell, Wikimedia)
3

IDENTIFICATION

Leaves long, pinnately compound (Figs. 4a, 5a) whose 

leaflets have smooth margins and slightly lobed bases 

tipped by raised glands (Figs. 4b, 5b)

Winged fruits 1 in (2.5 cm) long, turn from green/

yellow to orange/red to brown (Figs. 4c, 5c)

Leaf scars large, triangular, and edged by line of bundle 

scars (Fig. 4d, 5d)

Flowers small with 5 greenish-yellow petals, produced 

in large clusters

Native look-a-like trees include walnut and sumac

a b c d

Figure 4 (top), 5 (bottom). Key identification characteristics of TOH including (a) 

leaf shape, (b) leaflet glands, (c) seed morphology, and (d) leaf scars (Illustrations: 

Rachel K. Brooks, Virginia Tech; Photos: a. Leslie J. Mehrhoff, University of 

Connecticut; b,d. James H. Miller Forest Service; c. Chuck Bargeron, 

University of Georgia; a–d Bugwood.org)
4

TRADITIONAL CONTROL

Small seedlings can be hand-pulled from an area. 

Pulling older seedlings and saplings is more difficult, 

and roots left in the soil will re-sprout. Cutting large 

trees is not recommended as the sole control method 

as it often results in significant basal and root sprouting 

(Fig. 6). Moreover, cutting is impractical since multiple 

cuttings are required to deplete root reserves.

a

b

c

Figure 6.TOH stand (a) cut to the ground 2 March 2007, (b) re-sprouting 14 June 

2007, and (c) a monoculture 10 August 2007 (Photos: Scott Salom, Virginia Tech)

Several general-use herbicides are available that can be 

applied as foliar sprays, cut stump treatments, injections 

into the plant, or as basal sprays. These treatments 

are usually used on TOH at small scales but may also 

impact other nearby plants (non-target damage).

Chemical and mechanical control can remove TOH 

from a small area. However, because TOH is such 

an aggressive species, it will re-sprout, requiring 

multiple treatments and making large-scale, long-term 

eradication impractical and expensive.
5

BIOLOGICAL CONTROL

Due to the extensive negative impacts and invasive spread 

of TOH, as well as the shortcomings of traditional control 

methods for this species, there is an urgent need to develop 

biological control components for TOH Integrated Pest 

Management (IPM) programs. Bioherbicides may provide 

an efficient, inexpensive, and perennial control of TOH.

TOH’s native range was surveyed, and multiple potential 

classical biological agents were identified and targeted for 

further research. Of these, the weevil Eucryptorrhynchus 

brandti (Harold) demonstrated the most promise. As of 

2020, it is still undergoing host-range testing prior to 

consideration for its release in North America.

Early surveys of TOH in North America documented a 

lack of significant insect and pathogen agents. However, 

in 2002, a naturally occurring fungus was observed killing 

TOH trees in Pennsylvania (Fig. 7).

a

b

Figure 7. TOH trees exhibiting foliar symptoms of fungal infection (Photos: Rachel K. 

Brooks, Virginia Tech)
6

Verticillium nonalfalfae

HISTORY

Professor Don Davis and his students at the Pennsylvania 

State University first isolated this naturally occurring, 

deadly wilt-causing fungus from dead and dying TOH 

trees within forested areas in south-central Pennsylvania 

in 2002. 

Early research at Penn State University on inoculating 

the fungus into TOH at several sites in south-central 

Pennsylvania documented its potential as an effective 

biological control agent.

The disease spread naturally and rapidly, creating small 

populations of infected TOH (Table 1), which prompted 

further interest in the fungus as a biological control agent. 

The fungus was originally thought to be Verticillium 

albo-atrum but has since been formally identified as 

Verticillium nonalfalfae Inderbitzin et al. in 2011. 

Verticillium nonalfalfae was subsequently found on TOH 

in Virginia in 2008 by scientists at Virginia Tech and 

in Ohio in 2012 by U.S. Forest Service scientists. This 

promising, host-restricted biological control currently 

occurs over thousands of acres in these states. 

By 2011, natural spread of the fungus had resulted in the 

mortality of >30,000 TOH trees, effectively removing 

most TOH from the landscape at these inoculated sites.

Table 1. The spread of V. nonalfalfae from inoculated TOH to adjacent TOH at 4 sites 

in Pennsylvania, USA (Source: Don Davis, unpub. data 2011)

Site 2006 

# TOH inoculated

2010 

# TOH dead or dying

1 20 2,663

2 20 503

3 10 941

4 10 701
7

LIFE CYCLE AND IMPACT

As a soil-borne plant pathogen, Verticillium nonalfalfae 

attacks only plants, not humans or other organisms. This 

fungus produces resting structures (dormant melanized 

mycelia) that can survive in the soil or within plant debris. 

Stimulated by root exudates, these resting structures 

germinate, form mycelia that penetrate the tree’s root, 

and invade the xylem. The mycelia then spread quickly 

throughout the tree’s vessels, ultimately clogging the 

xylem and eliciting typical wilt symptoms. This disease 

develops fairly quickly and kills mature trees within just 

a few months. All TOH growth stages are susceptible, 

from seedling to mature tree, as well as the roots and 

subsequent root suckers. It is thus a strong candidate for 

use as a biological control agent.

SYMPTOMS

Foliar (leaves) symptoms: rapid onset of wilting, 

chlorosis (yellowing), necrosis (browning, Fig. 8), 

premature leaf drop, emergence of new leaves late in 

the season (epicormic sprouting and flushing, Fig. 9)

Wood symptoms: branch drop and orange coloration 

of wood visible when bark is removed (Fig. 10)

Stand symptoms: numerous diseased or dead TOH in 

one area (Fig. 11)

SAFETY

All native trees and understory plants that currently 

coexist with TOH are unaffected by this wilt, with the 

exception of striped maple, Acer pensylvanicum. Natural 

V. nonalfalfae infections have killed only 1% of associated 

striped maple, and striped maple populations were even 

observed increasing after TOH control. A large hostrange testing has been conducted on V. nonalfalfae isolate 

VnAa140. Of the 71 plant species tested in a greenhouse 

and in the field, significant disease impact occurred only 

on TOH. Work is underway to screen VnAa140 against a 

much larger list of nontarget plant species representative 

of agriculturally and ecologically important plants. 
8

Figure 8. Foliar symptoms on a V. nonalfalfae-inoculated TOH (Photo: Donald D. 

Davis, The Pennsylvania State University)

Figure 9. Epicormic sprouting on a V. nonalfalfae-inoculated TOH (Photo: Rachel 

K. Brooks, Virginia Tech)

Figure 10. Bark removed exposing color differences between healthy (left) and 

infected TOH (right) (Photo: Kristen Wickert, West Virginia University)

Figure 11. Aerial view of a TOH stand with several trees exhibiting foliar 

symptoms following V. nonalfalfae inoculations (Photo: The 

Pennsylvania State University)
9

SPREAD

Verticillium nonalfalfae can spread naturally from 

diseased to nearby healthy TOH through root contacts, 

soil movement, and transmission by insects. Due to this 

tree’s aggressive growth and clonal tendencies, TOH 

stands include many functional root grafts (roots that 

have grown together, Fig. 12). Consequently, the fungus 

readily spreads within a stand and is highly effective at 

controlling TOH over large areas. 

Figure 12. Excavated TOH roots showing a functional root graft (Photo: Kristen 

Wickert, West Virginia University)

Between or among stands, the fungus can be spread 

passively by ambrosia beetles, which feed on dead 

and dying trees. Euwallacea validus (Eichhoff) is 

the most common ambrosia beetle associated with 

symptomatic TOH. In laboratory studies, the weevil E. 

brandti demonstrated the ability to carry and transfer

V. nonalfalfae to TOH. These insects would be able to 

spread the fungus to TOH stands otherwise unreachable 

for short-range pathogen dissemination.

It is relatively easy to infect TOH by injecting a 

suspension of spores into the stem or by the “hack and 

squirt” method. Disease develops quickly, killing 100% 

of the trees within three months following infection. 

Because the fungus can spread naturally from diseased 

to nearby healthy TOH through root contact, this ability 

for natural spread would greatly increase the biological 

control efficacy of the pathogen and decrease application 

coverage needs.
10

Advantages of V. nonal

Native to the USA; not an introduced pathogen

Found killing TOH in Pennsylvania, Ohio, and Virginia 

Host-restricted; needs further confirmation 

Kills TOH of all growth stages

Can be mass produced and formulated

Easy to inoculate TOH with existing tools

100% TOH kill—consistent and fairly quick 

Disease spreads from infected to untreated TOH—a 

highly desirable feature

Could be integrated with other biological control 

agents (e.g., TOH weevil Eucryptorrhynchus brandti 

and spotted lanternfly pathogens and parasites)

BIOHERBICIDE POTENTIAL

An email survey was designed and conducted by the Florida 

Survey Research Center, University of Florida to determine 

the preference of using a registered bioherbicide as opposed 

to a chemical herbicide to control TOH. A total of 500 

potential users (e.g., highway departments, state parks and 

foresters, extension scientists, and pest control companies) 

were contacted. Of the 100 responders 1⁄3 said they were 

“very likely” and another 1⁄3 responded they were “likely” to 

use the bioherbicide instead of the chemical herbicide. 

Because V. nonalfalfae isolate VnAa140 from Pennsylvania 

has shown such excellent potential as a biocontrol agent for 

TOH, efforts are currently underway to register this isolate 

as a bioherbicide with the U.S. EPA. Registration would 

allow for the widespread general use of this biopesticide, in 

addition to its movement across state lines.

The registration process can take several years, although 

bio-based pesticides (e.g., bioherbicides) are usually 

granted “fast track” status and receive an expedited process. 

When registered by the U.S. EPA, this bioherbicide is 

expected to become a major component in IPM programs 

to control TOH. 
11

REGISTRATION PROCESS

A preliminary meeting (15 February 2018) between 

the U.S. EPA Biopesticides and Pollution Prevention 

Division, the private company BioProdex, and Dr. 

Michael Braverman (Manager Biopesticide, Organic and 

International Capacity Building Programs, IR-4 Project, 

Rutgers University, NJ) outlined the requirements and 

work plan for registration of V. nonalfalfae.

Beginning in 2019, BioProdex (contact Dr. Raghavan 

Charudattan), in collaboration with the USDA ARS 

U.S. Horticultural Research Laboratory, agreed 

to conduct laboratory and greenhouse trials on 

approximately 250 plant species to determine the 

pathogenicity of V. nonalfalfae isolate VnAa140, the 

host range of the isolate, and the potential non-host 

species at risk, if any. 

Dr. Braverman agreed to serve as Bioprodex’s EPA 

liaison throughout the registration effort and to advise 

and assist the company regarding agency rules and 

regulations, data requirements, submissions, reviews, 

and other matters. His services are provided free 

of cost, as part of the IR-4’s assistance to promote 

biopesticide registrations.

Sylvan Bio, Kittanning, PA, a renowned world leader 

in fungal biomass production, agreed to industrially 

develop isolate VnAa140 biomass for the proposed effort 

and, after EPA registration, serve as the manufacturer 

of the fungal bioherbicide product for BioProdex. 

A certified commercial toxicology lab must still be 

subcontracted to gather toxicity data on the fungal 

isolate according to EPA Tier 1 testing guidelines. 

Gathering empirical data and submitting a full 

registration data package to the EPA is expected to take 

3 years. An additional year might be needed to develop 

bioherbicide product specifications, application tools 

and methods, a pesticide label and use instructions, 

and packaging.

During the EPA registration review, the bioherbicide 

is expected to be available for field testing under an 

Experimental Use Permit.
12

WHAT YOU CAN DO

Because industrially developing and registering the 

fungus as a bioherbicide would provide a powerful tool 

to hasten the control of TOH, there is an urgent need to 

identify funding sources to support its registration.

It is estimated that a total of $185,000 is needed to 

complete the host range trials, and a total of $215,000 

is needed to complete the toxicology tests. These funds 

would cover studies conducted over 2 years and provide 

the initial critical data to determine whether or not 

to continue the registration process (e.g., field trials, 

formulation development). Research proposals have been 

submitted to potential funding sources (e.g., Farm Bill, 

Spotted Lanternfly Program, USDA Special Projects) to 

develop registration data, but to date funding has not 

materialized. 

Funding is imperative as this native fungus has been 

demonstrated as a highly effective bioherbicide that 

kills TOH and spreads naturally. It is the only long-term, 

environmentally compatible control for TOH, either as 

a standalone treatment or as a component for an IPM 

approach. Contact your state department of agriculture, 

department of forestry, or department of highways to 

inquire about the registration status of this fungus.

UNTIL V. NONALFALFAE IS REGISTERED

STOP

Movement of infected plant material or associated 

soil is highly discouraged as this practice can lead to 

the spread of other pests or diseases (such as spotted 

lanternfly or fusarium canker) 

Movement of V. nonalfalfae across state borders 

requires a government permit. Movement without a 

permit is punishable by law

Use, production, and sale of V. nonalfalfae as a 

bioherbicide requires U.S. EPA registration
The use of trade, firm, or corporation names in this publication is for the 

information and convenience of the reader. Such use does not constitute an 

official endorsement 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. 

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Booklet back cover image: A TOH stand whose center-most trees were 

inoculated with V. nonalfalfae two months prior to this photo (Photo: Rachel 

K. Brooks, Virginia Tech)
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