THE ROLE OF 

VERTICILLIUM WILT FUNGI

IN CONTROLLING THE INVASIVE

TREE-OF-HEAVEN

(AILANTHUS ALTISSIMA)

Rachel K. Brooks1

Kristen Wickert2

Joanne Rebbeck3

1

Dept. Plant Pathology, Physiology, and Weed Science, Virginia Tech, 

Blacksburg, VA 2

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

3

Northern Research Station, USDA Forest Service, Delaware, OH

FHAAST-2018-02

March 2018

Forest Health Assessment and 

Applied Sciences Team
This publication is available online at: 

https://www.fs.fed.us/foresthealth/

technology/pdfs/FHAAST-2018-02_

Verticillium_Wilt_Fungi.pdf

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/

Acknowledgments

The authors wish to thank Matthew Kasson (West Virginia 

University), Scott Salom (Virginia Tech), and Anton Baudoin 

(Virginia Tech) for their support of this project and assistance 

with this booklet. Funding for this project was provided by 

the USDA Forest Service Forest Health Protection Special 

Technology Development Program and Biological Control 

of Invasive Plant Program. The layout of this brochure was 

designed by Rachel Winston, MIA Consulting.
the goal of controlling

tree-of-heaven (ailanthus) 

is to protect our native forests, 

woodlots, agricultural lands, and

sensitive ecosystems by reducing

its presence and aggressive spread

KEY FINDINGS

Verticillium nonalfalfae is a native soil-borne 

fungus that causes a vascular wilt disease and 

has been found naturally killing Ailanthus (Fig. 1) 

in Pennsylvania, Virginia, and Ohio

V. nonalfalfae can rapidly spread throughout an 

Ailanthus stand after only a few one-time stem 

inoculations

Severe decline and spread by this speciesspecific V. nonalfalfae isolate is limited to 

Ailanthus, with no indications that other plant 

species would be severely impacted

Fig. 1. Ailanthus in the foreground are displaying wilting symptoms one 

month after being inoculated with Verticillium nonalfalfae. (Photo: Kristen 

Wickert, West Virginia University) Booklet front cover image: Foliar 

symptoms on V. nonalfalfae-inoculated Ailanthus (top) compared to uninoculated healthy Ailanthus (bottom) (Photo: Rachel K. Brooks, Virginia Tech)
2

AILANTHUS BACKGROUND 

INFORMATION

Deciduous hardwood tree native to eastern China 

that was brought to Pennsylvania in 1784 as an 

ornamental tree

Has spread throughout the northern and southern 

hemispheres, including most of North America 

where it has invaded over 40 US states

Invades our forests, outcompetes and displaces 

native vegetation important for wildlife habitat, 

timber, biodiversity, and recreational activities

Grows aggressively into right-of-ways and urban 

areas, and takes over agricultural lands in as little 

as a few years (Fig. 2)

Appears to help support other invasive species 

including the brown marmorated stink bug and 

the newly introduced spotted lanternfly

Grows quickly and spreads easily by producing 

thousands of seeds at an early age and sprouting 

clonally

Scientific name is Ailanthus altissima, but is also 

known as tree-of-heaven, Ailanthus, Chinese 

sumac, varnish tree, and stink tree

Fig. 2. Ailanthus infestation (Photo: Joanne Rebbeck, USDA Forest Service)
3

AILANTHUS 

IDENTIFICATION

Long, pinnately compound leaves (Figs. 3a, 4a), 

whose leaflets have smooth margins and slightly 

lobed bases tipped by raised glands (Figs. 3b, 4b)

Large amounts of seeds that turn from green/

yellow to orange/red to brown on female trees 

visible in late summer through winter (Figs. 3c, 4c)

Large triangular leaf scars that are edged by a line 

of bundle scars (Fig. 3d, 4d)

Smooth cantaloupe-skin-like bark 

Pungent, rotten peanut-butter odor when touched

Native look-a-like trees include walnut and sumac

a b c d

Fig. 3 (top), 4 (bottom). Key identification characteristics of Ailanthus 

including leaf shape (a), leaflet glands (b), seed structure (c), and leaf 

scars (d). (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

How Will Verticillium 

Fungi Help?

Chemical and mechanical control can remove 

Ailanthus from a small area. However, because 

Ailanthus is such an aggressive species, it 

will re-sprout, requiring multiple treatments 

and making large-scale, long-term eradication 

impractical and expensive

Research shows that V. nonalfalfae will be 

cost-effective, largely Ailanthus-specific, longlasting, and effective at removing Ailanthus 

from a landscape

V. nonalfalfae is easy to apply by land managers 

and homeowners, unlike herbicides. The fungus 

is currently not available to the public and 

must be cultured under sterile conditions in a 

laboratory setting

Recognizing Ailanthus 

Impacted by V. nonalfalfae

Foliar (leaves) symptoms: rapid onset 

of wilting, chlorosis (yellowing), necrosis 

(browning, Fig. 5), premature leaf drop, 

emergence of new leaves late in the season 

(epicormic sprouting and flushing, Fig. 6)

Wood symptoms: branch drop and orange 

coloration of wood visible when bark is 

removed (Fig. 7)

Stand symptoms: numerous disease or dead 

Ailanthus in one area (Fig. 8)
5

Fig. 5. Foliar symptoms on a V. nonalfalfae-inoculated Ailanthus 

(Photo: Donald Davis, The Pennsylvania State University)

Fig. 6. Epicormic sprouting on a V. nonalfalfae-inoculated Ailanthus 

(Photo: Rachel K. Brooks, Virginia Tech)

Fig. 7. Bark removed exposing color differences between healthy (left) and 

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

Fig. 8. Aerial view of an Ailanthus stand with several trees exhibiting 

foliar symptoms following V. nonalfalfae inoculations (Photo: 

The Pennsylvania State University)
6

What Has V. nonalfalfae

Research Proven?

It has been confirmed that V. nonalfalfae can 

spread within a stand to neighboring Ailanthus 

through functional root grafts (roots that have 

grown together, Fig. 9), effectively killing 

Ailanthus within an area

V. nonalfalfae isolates have been shown to 

cause severe and widespread decline only on 

Ailanthus in forest stands, and have little or no 

effect on other plants. Host-range testing of V. 

nonalfalfae has included over 70 species of 

plants with no major impact

V. nonalfalfae can be applied to Ailanthus using 

hack-and-squirt stem-injection methods (Fig. 

10) with most effective results achieved during 

spring-time inoculations

V. nonalfalfae can be cheaply and efficiently 

cultured in large quantities in a laboratory setting

Fig. 9. Excavated Ailanthus roots showing a functional root graft 

(Photo: Kristen Wickert, West Virginia University)

Fig. 10. Typical tools and procedure for hack-and-squirt inoculation 

methods appropriate for inoculating V. nonalfalfae into Ailanthus: (1) 

wound the plant with an axe or machete and then (2) inoculate the 

wound with the control agent using a pipette or a spray bottle. 

(Illustration: Rachel K. Brooks, Virginia Tech)
7

What to Expect in the 

Next Few Years:

Research will continue to focus on: 

insect vectors that may be able to help quickly 

spread the fungus from stand to stand 

best management practices to restore 

vegetation after Ailanthus has been removed 

climatic and geographic limits of V. 

nonalfalfae throughout Ailanthus’s invaded 

North American range. These V. nonalfalfae

isolates are currently only known to occur 

naturally in Pennsylvania, Virginia, and Ohio

determining any risk this V. nonalfalfae isolate 

has on other native species, including devil’s 

walkingstick (Aralia spinosa), American 

ginseng (Panax quinquefolius), staghorn 

sumac (Rhus typhina), and striped maple 

(Acer pensylvanicum)

examining any other risks associated with 

using V. nonalfalfae as a biocontrol agent

further work on V. nonalfalfae production at an 

operational level (for large-scale production, 

inoculation, and distribution)

Efforts to register V. nonalfalfae as a minor-use 

bio-herbicide with the US EPA are ongoing

After registration, large-scale production and 

distribution will hopefully be taken on by a 

business or university
8

Until Then 

Do’s and Don’ts

Don’t: 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 lantern fly or 

fusarium canker) 

Don’t: Movement of V. nonalfalfae across 

state borders requires a government permit. 

Movement without a permit is punishable by law

Don’t: Use, production, or sale of V. nonalfalfae 

as a bio-herbicide requires US EPA registration

Do: Continue to control Ailanthus using legal 

means (a combination of mechanical and 

chemical control) to limit future spread

Do: When controlling Ailanthus with current 

legal means, remember:

to target seed-bearing trees first

that a combination of chemical and mechanical 

control works best

to plan on resurveying and retreating the area 

yearly
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Booklet back cover image: An Ailanthus 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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