How To 

Identify, Prevent, and 

Control Oak Wilt 

United States Forest Service Northeastern Area 

Department of State & Private 

Agriculture Forestry 

NA–FR–01–11 
Authors 

Joseph G. O’Brien, Plant Pathologist 

USDA Forest Service 

Northeastern Area State and Private Forestry 

Forest Health Protection 

Manfred E. Mielke, Forest Health Specialist 

USDA Forest Service 

Northeastern Area State and Private Forestry 

Forest Health Protection 

Dale Starkey, Plant Pathologist 

USDA Forest Service 

Southern Region 

Forest Health Protection 

Jennifer Juzwik, Research Plant Pathologist 

USDA Forest Service 

Northern Research Station 

Illustrators 

Julie Martinez, Scientific Illustrator 

Minneapolis, Minnesota 

Juliette Watts, Scientific Illustrator 

Newtown Square, Pennsylvania 

Acknowledgments 

The authors thank Dr. Frank Tainter and 

Dr. David Appel for their reviews of the 

manuscript. We are also grateful to Steve Cook, 

Steve Kunde, Linda Haugen, and Jill Pokorny 

for helpful suggestions concerning content and 

to Roberta Burzynski and Sandy Clark for 

editing the manuscript and Deb Muccio for 

design and layout. 
How To
 

Identify, Prevent, and 

Control Oak Wilt 

United States 

Department of 

Agriculture 

Forest Service 

Northeastern Area 

State and Private Forestry 

NA–FR–01–11 

Newtown Square, PA 

August 2011 

www.na.fs.fed.us 
CAUTION: 

PESTICIDES 

Pesticide Precautionary 

Statement: 

Pesticides used improperly 

can be injurious to humans, 

animals, and plants. Follow 

the directions and heed 

all precautions on the 

labels. Store pesticides in 

original containers—out of reach of children 

and pets—and away from foodstuffs. Apply 

pesticides selectively and carefully. Do not 

apply a pesticide when there is danger of drift 

to other areas. Avoid prolonged inhalation 

of a pesticide spray or dust. When applying 

a pesticide it is advisable that you be fully 

clothed. After handling a pesticide, do not eat, 

drink, or smoke until you have washed. In case a 

pesticide is swallowed or gets in the eyes, follow 

the first-aid treatment given on the label, and 

get prompt medical attention. If the pesticide is 

spilled on your skin or clothing, remove clothing 

immediately and wash skin thoroughly. Dispose 

of empty pesticide containers by wrapping 

them in several layers of newspaper and placing 

them in your trash can. 

It is difficult to remove all traces of an herbicide 

(weed killer) from equipment. Therefore, to 

prevent injury to desirable plants do not use the 

same equipment for insecticides and fungicides 

that you use for an herbicide. 

NOTE: Registrations of pesticides are under 

constant review by the Federal Environmental 

Protection Agency. Use only pesticides that 

bear the EPA registration number and carry 

directions for home and garden use. 
Table of Contents
 

Introduction ......................... 1
 

How Infection Occurs: The Disease Cycle of 


Stump Extraction as a Substitute for 


Summary of Integrated Oak Wilt 


Northeastern Area State and Private 


Forest Service Southern Region State and 


Distribution.......................... 1
 

Hosts .............................. 2
 

Oak Wilt............................ 5


 Local Spread of Oak Wilt ............. 5


 Overland Spread of Oak Wilt........... 6
 

Symptoms.......................... 11


 Red Oak Group.................... 11


 White Oak Group .................. 12


 Texas Live Oak..................... 12
 

Diagnosis .......................... 14
 

Other Disorders of Oaks ............... 14


 Bacterial Leaf scorch ................ 14


 Oak Anthracnose .................. 14


 Oak Decline ...................... 15


 Twolined Chestnut Borer............. 16
 

Integrated Management of Oak Wilt ..... 16


 Preventing New Infection Centers ...... 16


 Remove Infected Trees ............ 17


 Avoid Injuring Healthy Trees ........ 17


 Controlling Existing Infection Centers ... 18


 Trenching and Vibratory Plowing..... 19


 Trenching ...................... 22


 Chemical Root Disruption .......... 22


 Chemical Control Using Fungicides..... 23
 

 Management Strategies .............. 24
 

Literature Cited...................... 25
 

Other References .................... 25
 

Glossary ........................... 26
 

 Forestry Offices..................... 29
 

Northern Research Station ............. 29
 

 Private Forestry Offices ............... 30
 

1 

Introduction 

Oak wilt is an aggressive disease that affects 

many species of oak (Quercus spp.). It is one 

of the most serious tree diseases in the Eastern 

United States, killing thousands of oaks each 

year in forests, woodlots, and home landscapes. 

Distribution 

Oak wilt was first identified in 1944. The fungal 

pathogen that causes the disease, Ceratocystis 

fagacearum, is thought by most to be native 

to the Eastern United States, but difficulty in 

isolating and identifying the fungus delayed 

recognition of the extent of its impact until 

the 1980s. Recent evidence suggests that oak 

wilt is an exotic disease that arrived in North 

America in the early 1900s. However, the fungus 

has never been reported by any country other 

than the United States, so its origin remains 

unknown. The disease has also become much 

more apparent in some local areas since the 

1980s because of increased tree wounding, due 

primarily to home construction in oak woods. 

The current known distribution of oak wilt is 

shown in red in figure 1. 

Figure 1.—In 2010, oak wilt was distributed over much 

of the Eastern United States. 
Hosts 

Oaks can be organized taxonomically into three 

main groups based on leaf shape and other 

characteristics: red oaks, white oaks, and live 

oaks. Trees in the red oak group have fan-shaped 

leaves with sharply pointed tips, those in the 

white oak group have fan-shaped leaves with 

rounded or blunt tips, and trees in the live oak 

group have oval leaves with pointed to rounded 

tips (figure 2). Oak species most commonly killed 

by the disease are listed in table 1. 

All species in the white oak group are 

moderately resistant to oak wilt, but if infected, 

trees in this group can be killed over a period of 

one to several years. Resistance in white oaks 

appears to be related to their physiology and 

anatomy. If white oaks are wounded or infected, 

or as part of the natural aging process, they tend 

to form minute, balloon-like plugs called tyloses 

in their sapwood vessels. These plugs make the 

wood of white oaks impermeable to water, and 

also appear to prevent the fungus from moving 

throughout the vascular system of the tree. 

The tendency for white oaks to form tyloses also 

explains why these are the species of choice for 

wood used in cooperage for storing wine and 

whiskey. The presence of tyloses ensures that 

barrels made from white oak wood will not leak. 

Throughout the range of oak wilt in the United 

States, red oaks are the most important hosts. 

However, susceptibility varies somewhat by 

species. Mortality in red oaks can occur within 3 

weeks after infection by the oak wilt pathogen 

under some circumstances. Recovery from oak 

wilt infections in red oaks can occur, but is rare. 

In Texas, live oak (Q. virginiana) is moderately 

susceptible to the disease, but because of its 

tendency to form large, root-connected clones 

2
 
Red Oaks Red Oaks 

Northern 

pin oak 

Northern 

red oak 

Texas red oak 

White Oaks 

Bur oak 

White oak 

Figure 2.—The three main groups of oaks are 

organized by leaf shape. 

3
 
Live Oaks 

Texas live oak 

Figure 2. Continued.—The three main groups of oaks 

are organized by leaf shape. 

through which the disease can spread, it is 

considered to be an important host and has 

sustained high levels of mortality. 

Although the disease is not known west of 

Texas, inoculation studies have shown that 

most oaks in the red oak group, including 

several western species, are susceptible to the 

disease and are at risk should the fungus ever 

be transmitted to them in their native habitat 

(Appel 1994). 

4
 
5 

Table 1. Oak species commonly killed by oak wilt.1 

Common name(s) Scientific name 

Northern species 

Black oak Q. velutina 

Bur oak2 Q. macrocarpa 

Northern pin oak Q. ellipsoidalis 

Northern red oak Q. rubra 

White oak2 Q. alba 

Southern species 

Blackjack oak Q. marilandica 

Scrub live oak Q. fusiformis 

Shumard oak Q. shumardii 

Southern red oak Q. falcata 

Texas live oak Q. virginiana 

Texas red oak (Spanish oak) Q. buckleyi 

1

 All red oaks in the Eastern United States are 

considered susceptible to oak wilt. 

2

 Infections are less common in these species and may 

take years to run their course. 

How Infection Occurs: The 

Disease Cycle of Oak Wilt 

The oak wilt fungus moves from tree to tree in 

two ways: underground through the roots or 

overland by insect vectors. 

Local Spread of Oak Wilt 

Most new tree infections occur when the fungus 

moves from an infected tree to a nearby healthy 

tree through connected root systems in a process 

called local spread (figure 3, lower pathway). 

The roots of trees in each oak group commonly 

graft to roots of other trees in the same group, 

forming a continuous underground network. 

When one tree in a group becomes infected and 

dies, the fungus spreads through the connected 

root systems, killing more trees and creating an 

infection center. 
Root grafts do not commonly occur between 

trees of different oak species groups, although 

exceptions occur. Usually a mix of species in a 

given location will retard local spread and limit 

the impact of the disease. However, root grafts 

often do occur between Texas live oaks and red 

oaks in mixed stands. 

Depending upon soil type and the mix of tree 

species in a forest or yard, infection of healthy 

trees through root grafts can occur at some 

distance (up to 100 feet or more) from an 

infected tree. Sandy soils are conducive to the 

formation of widespread root systems, increasing 

the likelihood of root grafts occurring farther 

away from a diseased tree. Some oak species, 

including northern pin oak and Texas live oak, 

often grow in large groups of similar-aged trees 

that share a common or clonal root system. Such 

situations can lead to rapid expansion of oak wilt 

centers if even one tree in the group becomes 

infected. 

Overland Spread of Oak Wilt 

New infection centers can occur if the fungus is 

carried from an infected tree to a fresh wound 

on a healthy tree by an insect in a process called 

overland spread (figure 3, upper pathway). 

Under certain moisture and temperature 

conditions, compact masses of fungal material 

that produce spores—variously called fungal 

mats, spore mats, spore pads, or pressure 

pads—sometimes form on oak trees that have 

been killed by oak wilt (figure 4). These mats 

form just under the bark and are in contact 

with both the bark and the infected sapwood 

of the tree. As the mats mature, they produce 

specialized, non-spore-producing structures 

that exert outward pressure on the bark (the 

“pressure pads”) and cause it to split, thus 

providing a route for insects to reach the mats 

(figure 5). 

6
 
7 

Figure 3.—The disease cycle of oak wilt. 

Figure 3, upper pathway.—Long-distance 

spread of oak wilt occurs when nitidulid beetles 

carry spores of the fungus from spore mats 

on infected trees to wounds on healthy trees, 

causing infection and death of the tree. Time 

from infection to mortality may be very short for 

red oaks and Texas live oak, or many years for 

members of the white oak group. 

Figure 3, lower pathway.—Local spread of oak 

wilt occurs when the fungus travels through the 

interconnected roots of infected and healthy 

trees. 
Figure 4.—An oak wilt spore mat with pressure pads 

(arrow). 

Figure 5.—Bark split caused by a pressure pad of the 

oak wilt fungus. 

8
 
9 

Figure 6.—Nitidulid beetles are primarily responsible 

for overland spread of oak wilt. 

Oak wilt spore mats emit a strong, fruity or 

wine-like odor that attracts many different 

species of nitidulid beetles (figure 6), also 

known as sap beetles. As they feed on or tunnel 

through the spore mats, nitidulid beetles often 

accumulate fungal spores on the surface of their 

bodies. 

Oak trees often sustain wounds caused by 

construction equipment, storms, pruning tools, 

or vandalism. Fresh wounds usually leak sap that 

attracts insects, including nitidulid beetles that 

have visited oak wilt spore mats. The overland 

movement of the fungus via nitidulid beetles 

that visit both spore mats on infected trees and 

wounds on otherwise healthy trees thus creates 

most new infection centers. 

Not all nitidulid beetles are vectors of the oak 

wilt pathogen. More than 12 beetle species are 

associated with oak wilt spore mats during the 

spring season in the North, but Colopterus and 

Carpophilus species are the most abundant. 
Furthermore, only Colopterus truncatus, 

Colopterus semitectus, Carpophilus sayi, and 

Epuraea corticina are known to carry the oak 

wilt pathogen to fresh wounds during the critical 

spring period. 

Spore mats can form only within a year after 

tree death, and only when air temperature and 

wood moisture are within a certain range. In 

the Northern United States, this combination 

of wood moisture and temperature commonly 

occurs in the spring of the year after the tree 

dies, or sometimes in autumn of the year the 

tree dies. As latitude decreases, the period of 

time during which mats form increases. In Texas, 

mats form at any time during the year, but 

most commonly in late fall and winter when the 

weather is cooler and wetter. In addition, spore 

mats are formed only on Texas red oak and 

blackjack oak, and never on Texas live oak. For 

this reason, red oak group species are important 

for establishing new infection centers in Texas. 

Spore mats usually do not form on trees smaller 

than 6 inches in diameter at breast height, 

although smaller trees can occasionally support 

mats. Across the range of oak wilt, most spore 

mats are produced on trees in the red oak group, 

but mats can also develop on bur oak. Mats do 

not form on other trees in the white oak group. 

Another group of insects—oak bark beetles— 

can also carry spores of the oak wilt pathogen 

and help create new infection centers. These 

beetles acquire spores of the fungus just prior 

to emerging from oak wilt-killed trees and 

subsequently transmit them when feeding in the 

crowns of healthy oaks. The relative importance 

of these beetles as vectors of this disease varies 

by region. Oak bark beetles are considered minor 

vectors in the Central United States, but may be 

more important in the Appalachians. 

10
 
11 

Symptoms 

Oak wilt disease symptoms progress differently 

in red oaks, white oaks, and Texas live oak. 

Red Oak Group 

Oak wilt is usually identified in red oaks by rapid 

leaf discoloration and wilting. Often the initial 

symptom is a subtle off-green color shift that 

may be visible in the upper portion of the tree 

crown. This symptom is apparent in the northern 

part of the disease range in late June to early 

July. Shortly after this initial color shift, the 

leaves begin to wilt from the top of the crown 

downward. As the disease progresses, individual 

leaves quickly discolor, taking on a bronzed 

appearance. The discoloration progresses around 

the margins of the leaf from the tip to the base 

(figure 7B). The progressing discoloration may 

be interrupted by the leaf veins, as shown in the 

white oak leaf in figure 7A, or may affect the 

entire upper portion of the leaf, as shown in the 

red oak leaf in figure 7B. 

Leaves are cast rapidly as the infection 

progresses. Commonly, infected trees are 

almost entirely defoliated within a few weeks of 

symptom onset. Fallen leaves usually are brown 

at the tips and margins, and sometimes green 

at the base and along the lower veins. Trees are 

often killed in groups or disease centers, when 

infection occurs through grafted roots. 

Occasionally the outer ring of vessels of diseased 

trees will be plugged with a brown substance 

that may be visible in cross sections as a ring 

or a series of dark spots through the outer 

sapwood, and in tangential cuts as longitudinal 

streaking of wood exposed after removing the 
bark. However, this is not always obvious to an 

untrained observer, especially in the red oaks. 

The discoloration may be very light or appear 

as flecks in such sections. Discoloration is most 

readily seen in tangential cuts on branches. 

White Oak Group 

White oaks usually die slowly, one branch at a 

time, over a period of one to many years. Leaf 

wilting and death occur in a similar fashion 

to that of red oaks, but these symptoms 

usually progress much more slowly in white 

oaks. Affected leaves exhibit a pattern of 

discoloration similar to that seen in red oaks, 

with discoloration proceeding from the margins 

to the base, sometimes interrupted by the leaf 

veins (figure 7A). Brown streaking in the outer 

growth rings is often readily apparent even to an 

untrained observer in infected white oaks and 

bur oaks, but this symptom may also be missing. 

Texas Live Oak 

Texas live oaks can wilt and die rapidly or slowly, 

depending on the timing of infection and 

weather conditions. However, they generally 

succumb within 1-6 months of infection. 

Diagnostic leaf symptoms are usually produced 

somewhere on the tree (especially in spring and 

fall). Leaves develop yellow (chlorotic) veins that 

eventually turn brown (necrotic), a symptom 

termed veinal necrosis (figure 7C). Affected 

leaves fall, and the tree crown progressively thins 

out until the entire tree is dead. Fallen leaves 

under the tree may show darker brown veins 

for months. Sometimes just the tips, margins, 

or interveinal portions of leaves will turn yellow 

or brown, but these symptoms are not always 

the result of oak wilt and are not as useful in 

diagnosing the disease. A small percentage of 

Texas live oaks may survive oak wilt infection 

indefinitely while suffering varying degrees of 

crown loss. 

12
 
13 

A 

B 

C 

Figure 7.—Symptoms of oak wilt in A. white oak, 

B. red oak, and C. Texas live oak. 
Diagnosis 

Accurate diagnosis of oak wilt is essential before 

costly control efforts are begun. Foresters, 

arborists, or pathologists experienced with oak 

wilt can often diagnose the problem in the field 

using host species, symptoms, and mortality 

patterns. Properly sampling suspect trees and 

culturing the samples in a qualified laboratory 

may be necessary in some cases. See the 

publication “How to Collect Field Samples and 

Identify the Oak Wilt Fungus in the Laboratory” 

for additional information. 

Other Disorders of Oaks 

The following oak disorders may sometimes be 

confused with oak wilt: bacterial leaf scorch, 

anthracnose, decline, and infestation with 

twolined chestnut borer. 

Bacterial Leaf scorch 

Oaks in both the red and white oak groups are 

susceptible to a bacterial disease that causes leaf 

symptoms similar to oak wilt. Symptoms include 

marginal leaf browning, branch mortality, and 

eventually tree death. Trees may be symptomatic 

for several years before the tree dies, and 

symptoms usually persist on infected branches 

from year to year. While marginal browning is 

common, water soaking, bronzing, and wilting 

symptoms are absent, and trees do not die from 

bacterial leaf scorch very quickly. 

Oak Anthracnose 

Trees in both the red and white oak group are 

susceptible to a group of fungal leaf diseases 

collectively called anthracnose that may be 

locally severe if weather conditions in the spring 

are cool and wet for an extended period during 

14
 
15 

leaf expansion, which favors development of 

such diseases. Anthracnose diseases are usually 

more severe in the lower portions of the crown, 

often causing the affected leaves to fall in early 

summer. Leaves in the upper portion of the 

crown may remain attached. Leaf symptoms 

usually include brown spots or patches that 

expand outward to the leaf margins. Although 

the leaves may be curled and distorted, they 

usually do not wilt. 

Oak Decline 

Oaks throughout the Eastern and Southern 

United States are susceptible to a decline 

syndrome, which is defined as a disease caused 

by the interaction of several injurious agents 

working simultaneously. In the case of oak 

decline these factors can include drought, 

defoliation, fungi that cause stem cankers or 

root diseases, and wood-boring beetles. The 

interaction of these factors may result in the 

decline and death of oak trees in a local or 

regional area. 

Oak decline symptoms vary greatly, and 

differentiating oak decline from oak wilt can be 

quite difficult. Indicators of oak decline include 

the absence of the typical leaf symptoms of oak 

wilt and the retention of dead leaves on the tree. 

Trees killed by oak wilt are usually completely 

defoliated and retain few living or dead leaves, 

but this may not be a consistent symptom for 

red oaks in the South. 

Oak wilt usually occurs in discrete, spreading 

pockets of mortality, with trees on the margins 

of the infection center becoming infected over 

time. Declines may occur in discrete pockets, 

or over a fairly large area, but do not typically 

spread outward from an initial infection center. 
Trees in decline may die over a period of years, 

or may ultimately survive a decline episode with 

only dead branches in the crown. 

Twolined Chestnut Borer 

The twolined chestnut borer (Agrilus bilineatus) 

is an insect that attacks oaks, especially 

those weakened by drought or defoliation. 

Larvae of the insect make tunnels in the inner 

bark, causing branch or even tree mortality. 

Symptoms usually begin in the upper portion 

of the crown and proceed downward, but this 

pattern is variable. The insects leave a distinctive 

“D-shaped” exit hole about 1-2 mm in diameter 

when they mature and leave the tree. Initial 

symptoms are usually single or scattered dying 

branches that often retain brown leaves until 

autumn. This insect is often part of the oak 

decline syndrome mentioned above. 

Integrated Management of 

Oak Wilt 

Oak wilt can be managed with a variety of 

strategies that prevent new infection centers and 

limit the expansion of existing infection centers. 

A good management program for oak wilt will 

include all of these strategies for combating the 

disease. 

Preventing New Infection Centers 

Once an oak tree becomes infected with oak 

wilt, there is no known chemical treatment 

that is capable of “curing” the disease; 

however, fungicide research is continuing. The 

development of new oak wilt pockets can be 

avoided, however, by either preventing the 

development of spore mats of the fungus on 

diseased trees or by preventing the transfer of 

fungal spores to healthy trees. In practice this 

16
 
17 

involves removing dead or diseased trees and 

avoiding injury to healthy trees. 

Remove Infected Trees 

Trees that are infected with or have died from 

oak wilt should be removed and properly 

treated to prevent development of spore mats. 

These treatments include debarking, chipping 

or splitting, and drying the wood. Covering 

dead wood with plastic, burying the edges for 

6 months, and then air drying for a similar time 

will kill the fungus and any associated insects. 

Trees that die in summer should be removed and 

treated before the following spring, which is 

when new spore mats can develop. If the wood 

is sufficiently dried, however, spore mats will not 

develop. 

A word of caution: Removing a diseased 

tree that is still living may actually facilitate 

the spread of the disease by accelerating 

the movement of the fungus into adjacent 

trees that are grafted to it by the roots. To 

avoid this problem, disrupt interconnected 

roots before removing living diseased trees 

as described in the section on “Controlling 

existing infection centers.” 

Avoid Injuring Healthy Trees 

Freshly wounded trees that are growing outside 

of existing oak wilt centers can be visited by 

beetles transporting spores of the fungus. 

Because open wounds create avenues for 

infection, damage to trees from construction, 

pruning, or severe storms may lead to new 

infection centers. Avoid injury to oaks during 

favorable conditions for infection, which in 

the North occur in spring and early summer, 

when spore mats are present and the beetles 

are flying. Favorable conditions usually occur 

between April 15 and July 1 in the Lake States 

and over a correspondingly longer period of time 

to the south. In Texas, avoid damage to oak trees 

from February through June. 
Preventing injury caused by human activity is 

especially effective in avoiding the establishment 

of new infection centers. In particular, pruning 

or construction activities in or near oak woodlots 

during the susceptible period often results in 

injury to oak trees that leads to infection. 

If construction activity, tree removal, or pruning 

is unavoidable, or if storms injure oak trees 

during the critical period, the wounds should be 

treated with a commercial tree paint or wound 

dressing. If whole trees are removed during the 

critical period, the stumps should also be treated 

with tree paint. It is very important that the 

fresh wounds be treated immediately because 

the insects that carry spores of the pathogen 

are often attracted to these wounds within a 

very short time. Tree paints are normally not 

recommended for general use, but using these 

products in this situation can protect trees 

from oak wilt. In the North, tree paints are 

not necessary if trees are wounded during the 

dormant season; however, judicious use during 

the rest of the year is recommended. From 

Missouri to Texas, use tree paint immediately 

after trees are wounded at any time of the year. 

Controlling Existing Infection Centers 

Once the oak wilt fungus becomes established 

in a stand that includes a high proportion of 

oak, it will often continue to spread through 

the grafted root systems of the trees, infecting 

healthy oaks. 

Disrupting the connections between the roots 

of infected and healthy trees limits the spread 

of oak wilt and is an effective control measure. 

Infected trees and their roots will usually die 

before root grafts can be re-established. The oak 

wilt fungus does not survive in the root systems 

of dead trees for more than a few years. 

18
 
19 

The potential for spread of oak wilt through 

grafted roots is especially high after a diseased 

tree is removed or dies. While a diseased tree 

is still living and intact, there is some resistance 

to fungal spores moving through root grafts 

into the roots of healthy trees. The removal or 

death of a diseased tree removes this natural 

resistance to spore movement, and spores may 

then travel more freely through interconnected 

roots. Therefore, the timing of a root disruption 

treatment is critical. Roots should be disrupted 

before an infected tree dies or is removed, or 

within a short time of tree death, for maximum 

protection of healthy trees. 

Interconnected root systems can be disrupted 

with a trencher, vibratory plow, or other 

equipment. 

Trenching and Vibratory Plowing 

Cutting roots with a trenching or cutting tool 

effectively controls the expansion of oak wilt 

pockets. In the Lake States, where deep and 

sandy or loamy soils are common, using a 

vibratory plow with a 5-foot blade (figure 8) 

is the preferred method of disrupting grafted 

root systems. The vibratory plow consists of 

a mechanical shaker unit with an attached 

blade that is pulled behind a tractor. The blade 

penetrates to a depth of about 5 feet, and cuts 

through the roots of oaks that may be grafted 

together. While oak roots may extend deeper 

than 5 feet in the soil, most root grafts are 

disrupted by trenching or plowing to that depth. 

Standard trenching tools do considerably more 

damage to the site, and the result is a much 

more apparent plow line than that caused by 

the vibratory plow. In Texas, shallow, rocky soils 

and even-layered rock often necessitate the use 

of a rock saw for disrupting oak roots. A chain 

trencher, backhoe, or ripper bar can sometimes 

be used. Trench depth should be about 5 feet, 

although this may be difficult to achieve in all 

situations. 
Figure 8.—A vibratory plow is sometimes used to 

disrupt grafted roots to prevent local spread of oak 

wilt. 

The lines cut by these trenching implements are 

usually referred to as barrier lines (figure 9). 

Successful disruption of root grafts to protect 

healthy trees close to an oak wilt infection 

center often requires that two or more parallel 

or intersecting lines be made. Primary barrier 

lines are those expected to have a good chance 

of protecting trees outside the lines. In addition, 

secondary barrier lines are often used to help 

ensure that the root graft disruption is effective. 

Separating groups of asymptomatic oaks from 

each other within the primary line may also save 

additional trees (figure 9). 

Root graft disruption can be made even more 

effective by removing all oak trees inside the 

barrier lines following plowing or trenching. 

Removing these trees and optionally treating the 

stumps with an herbicide helps ensure that all 

of the oak roots inside the barrier will die before 

root grafts can be re-established. This practice 

is sometimes referred to as cut to the line. 

Although this is a radical treatment, it may be 

useful in areas where oak wilt eradication is the 

goal. Assume that all trees removed are infected 

with the oak wilt fungus and destroy or treat 

them on site. 

20
 
21 

Figure 9.—This plan of a home landscape shows 

possible locations of vibratory plow lines for control 

of oak wilt. All trees are oaks. Brown trees are 

infected or dead; green trees are healthy. The solid 

red lines indicate primary barriers; the dashed lines are 

secondary barriers. 
Stump Extraction as a Substitute for 

Trenching 

In locations where the use of a vibratory plow or 

trencher is not practical because of infrastructure 

issues or boulder-laden soils, a strategy that 

involves cutting trees and uprooting the stumps 

may be a viable alternative. This procedure 

involves cutting all infected trees in an infection 

center as well as a buffer of nonsymptomatic 

trees around the infection center. Stumps of 

all cut trees are pulled from the ground using 

an excavator, which breaks many of the root 

connections between trees. Alternatively, 

trees and root systems can be pushed up and 

piled with a bulldozer. All cutting and stump 

extraction should be done during the dormant 

season. 

This technique works best for new, smaller 

infection centers because the stumps can be 

removed before the fungus moves from the 

boles into the root systems of infected trees. It is 

also best suited to rural or forested areas where 

infrastructure is absent and drastic vegetative 

disturbance is more acceptable. If this technique 

is used, it is likely that followup treatments will 

be needed. However, this technique has proven 

effective where trenching or plowing is not 

feasible. 

Chemical Root Disruption 

Biocidal chemicals have been used in the past 

to disrupt root grafts in trees, including oaks. 

These chemicals are very dangerous and difficult 

to work with, but can sometimes be used in 

areas where vibratory plowing or trenching is not 

an option because of buried utilities and septic 

tanks, or steep slopes. Holes are drilled into the 

soil at prescribed intervals and the chemical is 

poured into the holes, where it diffuses into the 

soil and kills the roots in a localized area. These 

chemicals are restricted-use pesticides; they must 

be applied by a licensed pesticide applicator 

22
 
23 

who has been trained in their use. In addition, 

these chemicals are costly, may damage the 

trees, and are effective only in uniformly textured 

soils where chemical distribution is even and 

predictable. 

Chemical Control Using Fungicides 

Fungicides have been developed that may be 

effective in preventing oak wilt when injected 

into living oak trees without active symptoms. 

A single treatment can protect red oaks from 

developing symptoms for 2 years following 

injection. In Texas live oaks, such treatments 

have prevented mortality in many cases, 

although foliar thinning usually occurs and 

can be substantial. Use of these fungicides is 

warranted when infection of high-value trees via 

local spread through root systems is imminent. 

These fungicides are apparently unable to stop 

already infected live oaks and red oaks from 

dying. Those currently available utilize some 

form of a chemical called propiconazole in the 

formulation. Such treatments create their own 

problems, including the necessity of wounding 

the tree to inject the fungicides. 

The cost of the fungicide is high, so only highvalue trees should be considered for treatment. 

Contact your county extension office for current 

advice on the use of chemicals for control of oak 

wilt. 
Summary of Integrated Oak 

Wilt Management Strategies 

Effective oak wilt management programs use a 

variety of strategies to limit the spread of oak 

wilt. Some of the practices and policies that can 

be used in combination to effectively manage 

oak wilt include the following: 

Avoid wounding oaks during critical 

infection periods. 

•	 If pruning is necessary, or if wounds occur on 

oak trees during the critical infection period, 

apply tree wound dressings or paints as soon 

as possible to prevent transmission of oak 

wilt. 

•	 Develop and enforce construction ordinances 

and utility pruning guidelines that minimize 

wounding of oak trees. 

•	 Use public service announcements, billboards, 

and flyers to raise awareness of the dangers 

of wounding oaks during susceptible periods. 

Use a vibratory plow line, trench barriers, 

stump extraction, or chemical disruption of 

roots to isolate pockets of oak wilt. 

•	 Communities and neighbors should join 

together to lower the cost of these tools and 

achieve more complete and effective local 

control. 

•	 Use root graft disruption, use cut-to-the-line 

practices, and treat stumps with herbicides to 

greatly reduce or eradicate oak wilt in local 

areas. 

Remove and properly treat oaks killed by 

oak wilt by debarking, chipping, or splitting 

and drying the wood before the spring 

following the tree’s death. 

•	 Do not move infected wood offsite without 

debarking, chipping, or properly drying it. 

Do not move or store firewood from infected 

24
 
25 

stands near healthy oaks without proper 

treatment. 

•	 Use and enforce city codes and ordinances 

that mandate removal and treatment of dead 

oak trees. Such ordinances can significantly 

reduce the chances for overland transmission 

of oak wilt. 

Use appropriate fungicides to protect 

very high-value trees at imminent risk of 

infection through root-to-root transmission. 

Literature Cited 

Appel, D.N. 1994. The potential for a California 

oak wilt epidemic. Journal of Arboriculture. 

20(2): 79-86. 

Other References 

Appel, D.N.; Cameron, R.S.; Wilson, A.D.; 

Johnson, J.D. 2008. How to identify and 

manage oak wilt in Texas. How-To SR-1. New 

Orleans, LA: U.S. Department of Agriculture, 

Forest Service, Southern Research Station. 7 p. 

Cervenka, V.J.; Skalbeck, T.C.; Kyhl, J.F.; 

Blackford, D.C.; Juzwik, J.J.; Seybold, S.J. 

2001. How to identify common nitidulid 

beetles associated with oak wilt mats 

in Minnesota. HT-71. St. Paul, MN: U.S. 

Department of Agriculture, Forest Service, 

North Central Research Station. 13 p. 

French, D.W.; Juzwik, J.J. 1999 (revised). Oak 

wilt in Minnesota. Extension Publication MI03174-GO. Minnesota Extension Service, 

St. Paul. 5 p. 
Pokorny, J. 1999. How to collect field samples 

and identify the oak wilt fungus in the 

laboratory. NA-FR-01-99. St. Paul, MN: 

U.S. Department of Agriculture, Forest Service, 


Northeastern Area State and Private 


Forestry. 12 p.
 

Glossary 

Anthracnose 

A group of fungal diseases that affect the leaves 

of many tree species. Anthracnose symptoms 

may be confused with those of oak wilt. 

Chlorosis (chlorotic) 

A loss of green color in leaves that results in a 

yellow discoloration. 

Cut to the Line 

The practice of removing all oaks, living or 

dead, inside the primary barrier line when using 

trenching to control local spread of oak wilt. 

Infection Center 

A localized group of trees that has been affected 

by a disease. The disease may spread from the 

margins of the infected group. 

Local Spread 

Spread of oak wilt from diseased to healthy 

trees through root-grafted, interconnected root 

systems. 

Long-distance Spread 

See Overland Spread 

Necrosis (necrotic) 

A brown discoloration of leaves that indicates 

dead tissue. 

26
 
27 

Nitidulid Beetles 

Beetles in the family Nitidulidae, sometimes 

called sap beetles. These beetles have been 

determined to be the primary carriers of fungal 

spores of the oak wilt pathogen to healthy trees. 

Overland Spread 

Spread of oak wilt by nitidulid beetles from 

spore mats on infected trees to open wounds 

on healthy trees. Oak bark beetles can also help 

spread oak wilt. 

Pressure Pad 

See Spore Mat, Spore Pad 

Primary Barrier Line 

A trench cut to disrupt grafted roots of oak. If 

two lines are used, the primary barrier line is 

the one expected to have the better chance of 

protecting trees outside the line (see Secondary 

Barrier Line). 

Root Graft 

Roots that have grown together so that a graft 

union is made between the conducting tissues 

of both roots. The oak wilt pathogen can move 

through grafted roots between infected and 

healthy trees to cause new infections. 

Secondary Barrier Line 

A trench cut to disrupt grafted roots of oak. If 

two lines are used, the secondary barrier line is 

the one expected to have the lesser chance of 

protecting trees outside the line (see Primary 

Barrier Line). 
Spore Mat, Spore Pad 

A structure produced by the oak wilt fungus at 

the bark-wood interface of oaks killed by the 

disease. Development of the structure causes 

the bark to split, exposing the mat below. 

The mat is covered with the spores of the oak 

wilt pathogen, which are picked up by visiting 

nitidulid beetles. 

Tyloses 

Microscopic structures that are produced in the 

conducting vessels of white oaks, which block 

the movement of water and fungal spores within 

the tree. The rapid development of tyloses may 

explain the difference in susceptibility between 

white oaks and red oaks. 

Vectors 

Organisms (such as insects, mites, or nematodes) 

or higher animals (such as birds or rodents) that 

carry a pathogenic agent to a susceptible host. 

Veinal Necrosis 

Dark yellow or brown discoloration that occurs 

along the veins of leaves. 

Vibratory Plow 

A shaker unit with a 5-foot blade pulled behind 

a tractor that is used to disrupt the grafted root 

systems of oaks to prevent spread of oak wilt. 

28
 
29 

 

 

Northeastern Area State and 

Private Forestry Offices 

Headquarters Office 

Northeastern Area State and Private Forestry 

USDA Forest Service 

11 Campus Boulevard, Suite 200 

Newtown Square, PA 19073 

Durham Field Office 

Northeastern Area State and Private Forestry 

USDA Forest Service 

271 Mast Road 

Durham, NH 03824-0640 

Morgantown Field Office 

Northeastern Area State and Private Forestry 

USDA Forest Service 

180 Canfield Street 

Morgantown, WV 26505-3101 

St. Paul Field Office 

Northeastern Area State and Private Forestry 

USDA Forest Service 

1992 Folwell Avenue 

St. Paul, MN 55108-1099 

Northern Research Station 

USDA Forest Service 

1992 Folwell Avenue 

St. Paul, MN 55108-1099 
Forest Service Southern 

Region State and Private 

Forestry Offices 

Headquarters Office 

USDA Forest Service 

Southern Region 

State and Private Forestry 

Forest Health Protection 

1720 Peachtree Road, NW 

Atlanta, GA 30309-2417 

Alexandria Field Office 

USDA Forest Service 

Southern Region 

State and Private Forestry 

Forest Health Protection 

Alexandria Field Office 

2500 Shreveport Hwy. 

Pineville, LA 71360 

Asheville Field Office 

USDA Forest Service 

Southern Region 

State and Private Forestry 

Forest Health Protection 

Asheville Field Office 

200 W.T. Weaver Blvd. 

Asheville, NC 28804 

30
 
 

The United States Department of Agriculture (USDA) prohibits 

discrimination in all its programs and activities on the basis of 

race, color, national origin, age, disability, and where applicable, 

sex, marital status, familial status, parental status, religion, 

sexual orientation, genetic information, political beliefs, reprisal, 

or because all or part of an individual’s income is derived from 

any public assistance program. (Not all prohibited bases apply 

to all programs.) Persons with disabilities who require alternative 

means for communication of program information (Braille, 

large print, audiotape, etc.) should contact USDA’s TARGET 

Center at (202) 720-2600 (voice and TDD). To file a complaint 

of discrimination, write to USDA, Director, Office of Civil Rights, 

1400 Independence Avenue, S.W., Washington, D.C. 20250­

9410, or call (800) 795-3272 (voice) or (202) 720-6382 (TDD). 

USDA is an equal employment opportunity provider and 

employer.