This year has brought a lot of storms which are usually accompanied by strong winds. These strong winds and downdrafts are the culperate for many of the damaged and up rooted trees although ground saturation plays a big role as well. Always remember that storm damaged trees are some of the most dangerous. The reason for this is because after the tree is damaged there can be anything from pressure loaded branches to stress fractures that typically can't be seen so it is always better to give us a call at 262 646 3735, and we will take care of it for you. Here is a study done by the unversity of georgia on wind loads on trees.
Storm Wind Loads
On Trees
by Dr. Kim D. Coder, Warnell School, University of Georgia Feb. 2007
Trees must withstand wind to survive. Wind and gravity both impact trees in storms, but the dominant load is from wind. Storm winds push on tree crowns and stems causing root plates to rock. The result of storm winds are forces twisting and bending tree parts causing either the part to fail or the supporting soil to fail. Treessense structural stress and attempts to minimize failures through reactive growth. Trees modify their structure over time as they are challenged by wind. Trees are biologically designed to sustain average wind loads. What are the loads applied by storms to trees?
Sailing Along
A tree has a large sail area (leaves and twigs) held upright high into the air by a tapered mast (stem). The stem is woven onto a thick horizontal mat of large structural roots at the stem base which forms a root plate. Rapidly tapering roots grow away from the stem base to provide the tree with an absorbing surface. The center of gravity (effective weight center) of a tree is usually somewhere in the middle of the stem above the root plate. Gravity is pulling down on the tree all over but has a total effect focused at the center of gravity. Wind is pushing the tree around its center of gravity. The weight of the tree is pulled down onto the soil surface. As long as its center of gravity remains positioned above its supporting base, the stem is stiff enough to keep the tree upright. If the center of gravity for a tree is not positioned over its supporting base, gravity may topple the tree if the tensile and compressive strength of the stem and root base is inadequate. Storm winds can push the center of gravity in the stem out from over its supporting base. The combined result is wind moving the tree laterally and gravity pulling the tree downward, providing a rotation force rolling the tree out of the ground -- a load wheel.
Gravity
Trees seldom fail under their own weight -- external loads stress and strain the tree until failure. Gravity loads trees in tandem with wind to initiate these failures, but wind loads greatly exceed gravity loads in most
situations. Wind is an acute mechanical variable for which trees must constantly adjust growth processes. Gravity is a chronic stress and strain with which trees must cope. Adding mass to a tree in the form of growth
(size, extent, and reach), or in applied water, ice or snow loads, can magnify gravity’s impact on the tree, causing fiber creep (permanent tissue changes) and failures. But, it is storm winds which push tree structures to their limits.
Impact Trinity
In order to more clearly understand storm initiated failures in trees, wind loads must be fully appreciated.
Wind has three primary components which impact trees: 1) velocity or speed (mile per hour or feet per second); 2) acceleration (velocity changes over time or velocity squared); and, 3) throw weight (mass of air)and its contents).
PUBLICATION
SFNR07-3
Thursday, September 29, 2011
Sunday, March 6, 2011
WInter Tree Damage
Damage to Trees During Cold Weather:
Winter tree damage can occur from any of a long list of cold related problems. You need to realize that tree damage is not generally caused by an unusually cold winter, but from extreme temperature fluctuations and the timing of these cold weather extremes during the dormant period and into the growing period.
Here are the most common causes of winter tree damage.
Extreme and Rapid Temperature Changes:
Trees much prefer slowly falling temperatures and a period of acclimation. Trees that are dormant but not fully acclimated can be stressed or injured by a sudden, hard freeze. Wild drops in temperature following mild weather can cause injury to woody plants. Extended periods of mild winter weather can cause a tree to resume growth making them vulnerable to injury from rapid temperature drops.
Low Temperature Injury and "Frost Crack":
Frost injury can occur when a tree is growing during early fall or late spring and a freeze injures or kills vulnerable tree tissue. To avoid frost damage, plant locally adapted trees, cover trees if frost is expected, avoid frost-prone sites and lay off nitrogen fertilizer at the end of the growing season. "Frost crack" can cause serious damage to trees by lengthening already existing wounds after repeated freezes.
Winter Injury Called Sunscald:
Winter burn is a common conifer problem. Rapid temperature change on the south side facing the sun can cause needles to burn. Drying is caused by warm conditions taking tree moisture while frozen ground and tissue restrict plant water flow. Planting hardy trees, mulching, wrapping and avoiding areas with sudden temperature can help. Sunscald can occur in late winter or early spring when the temperature is above freezing during the day and below freezing at night. Shading or wrapping can help.
Late Spring Freezes:
Once spring tree growth has begun, a late spring frost can cause damage. This is especially harmful if the freeze takes place after an early spring warming period. Succulent, new tree tissue turns flaccid, appears watersoaked, and withers within a short time. The symptoms of a severe late spring freeze resembles several diseases. Freeze injury appears suddenly after a hard frost while diseases generally occur throughout the year and take much more time to develop.
Frozen Roots:
This type of damage is usually associated with newly planted seedlings and container grown trees and only after freezes that extend over a long periods of time. Plants with frozen roots may wilt and decline after growth resumes in the spring.
With all of these problems that can happen in the winter it is important to get your trees examined by one of our professional arborists to ensure the longevity and health of your trees.
Winter tree damage can occur from any of a long list of cold related problems. You need to realize that tree damage is not generally caused by an unusually cold winter, but from extreme temperature fluctuations and the timing of these cold weather extremes during the dormant period and into the growing period.
Here are the most common causes of winter tree damage.
Extreme and Rapid Temperature Changes:
Trees much prefer slowly falling temperatures and a period of acclimation. Trees that are dormant but not fully acclimated can be stressed or injured by a sudden, hard freeze. Wild drops in temperature following mild weather can cause injury to woody plants. Extended periods of mild winter weather can cause a tree to resume growth making them vulnerable to injury from rapid temperature drops.
Low Temperature Injury and "Frost Crack":
Frost injury can occur when a tree is growing during early fall or late spring and a freeze injures or kills vulnerable tree tissue. To avoid frost damage, plant locally adapted trees, cover trees if frost is expected, avoid frost-prone sites and lay off nitrogen fertilizer at the end of the growing season. "Frost crack" can cause serious damage to trees by lengthening already existing wounds after repeated freezes.
Winter Injury Called Sunscald:
Winter burn is a common conifer problem. Rapid temperature change on the south side facing the sun can cause needles to burn. Drying is caused by warm conditions taking tree moisture while frozen ground and tissue restrict plant water flow. Planting hardy trees, mulching, wrapping and avoiding areas with sudden temperature can help. Sunscald can occur in late winter or early spring when the temperature is above freezing during the day and below freezing at night. Shading or wrapping can help.
Late Spring Freezes:
Once spring tree growth has begun, a late spring frost can cause damage. This is especially harmful if the freeze takes place after an early spring warming period. Succulent, new tree tissue turns flaccid, appears watersoaked, and withers within a short time. The symptoms of a severe late spring freeze resembles several diseases. Freeze injury appears suddenly after a hard frost while diseases generally occur throughout the year and take much more time to develop.
Frozen Roots:
This type of damage is usually associated with newly planted seedlings and container grown trees and only after freezes that extend over a long periods of time. Plants with frozen roots may wilt and decline after growth resumes in the spring.
With all of these problems that can happen in the winter it is important to get your trees examined by one of our professional arborists to ensure the longevity and health of your trees.
Thursday, May 6, 2010
Satisfied Customers
Dear Mike,
Please tell your guys thanks for doing a good job. I appreciate good workmanship- something you don't find everywhere these days, I know that the guys get paid for their work but they also need to be thanked as well. I will be contacting you for future work
Thanks, Bob *******
Dear Mike,
I just wanted to drop you a thank-you letter on the great work Ken, Ben and Jason did for us trimming our trees. They are all experts in their profession. They were very understanding of our wishes and concerns, friendly and courteous. The two times we've had your crew out to do some work for us they managed to remove trees and branches that were extremely tangled in other trees above and below them without damaging the good trees that we wanted to save. I watched the crew work and was impressed with their coordination, attention to safety and with how well they worked together. Their cleanup after they were finished left our yard loooking better than before they arrived. Your prices were better than other tree services we had out to bid on the project. We highly recommend Bark River Tree Service to anyone looking for a quality Tree Service. Thank you again, our appreciation goes out to Ken, Ben and Jason.
Sincerely,
Michael **********
Please tell your guys thanks for doing a good job. I appreciate good workmanship- something you don't find everywhere these days, I know that the guys get paid for their work but they also need to be thanked as well. I will be contacting you for future work
Thanks, Bob *******
Dear Mike,
I just wanted to drop you a thank-you letter on the great work Ken, Ben and Jason did for us trimming our trees. They are all experts in their profession. They were very understanding of our wishes and concerns, friendly and courteous. The two times we've had your crew out to do some work for us they managed to remove trees and branches that were extremely tangled in other trees above and below them without damaging the good trees that we wanted to save. I watched the crew work and was impressed with their coordination, attention to safety and with how well they worked together. Their cleanup after they were finished left our yard loooking better than before they arrived. Your prices were better than other tree services we had out to bid on the project. We highly recommend Bark River Tree Service to anyone looking for a quality Tree Service. Thank you again, our appreciation goes out to Ken, Ben and Jason.
Sincerely,
Michael **********
Thursday, February 25, 2010
Spring is quickly approaching and now is the time to start thinking about getting your trees trimmed and ready for the summer. At Bark River Tree Service we are here to serve you, we offer a complete line of services, one of which being (TPM) Total Property Maintainence, this includes the maintainence of everything green on your property. We have just added an attatchment to our T-250 that allows us to reach over retaining walls and even into the water to retrieve trees and or limbs with the slightest of ease. Any job big or small we can handle them all. I will be sure to attatch a picture to the next blog so you can see what the new attatchment is capable of.
Monday, February 15, 2010
T 250 Track Loader w/ Fecon Carbon Toothed Shredder Attatchment
Here is our solution to Buckthorn, Honeysuckle and basically anything you can throw at it.
It is a T250 Track Loader w Fecon Attatchment, capable of conquering any size and type of Job whether it is brushing in a marsh for hunting lanes or removal of invasive species we have got the right tools for the job.
It is a T250 Track Loader w Fecon Attatchment, capable of conquering any size and type of Job whether it is brushing in a marsh for hunting lanes or removal of invasive species we have got the right tools for the job.
Thursday, January 7, 2010
Hello Everyone Merry Christmas and a Happy New Year from Bark River Tree Service. This has been a good month for Bark River Tree Service; we have been staying busy despite the cold weather. We have been clearing an area of forest that has been taken over by invasive species, species such as
Buckthorn,
Buckthorn,
By the time we were done we had reclaimed over three acres of land. After seeing how efficiently our crew and equipment work and the little impact our equipment has on the ground the customers is having us come back for a second stage removal on yet another area of his property. We are thankful to have customers who recognize and appreciate our hard work. With that being said THANK YOU to all of our loyal Customers.
This past Saturday Boss man (Mike Doering) threw a Christmas party for the crew and friends, he cooked everyone large T-Bone Steaks and Potatoes with all the fixing’s, needless to say it was a good time and everyone enjoyed themselves.
I will keep everyone informed on the happenings here at Bark River Tree Service and until next time Happy New Year.
Ben Costa on Behalf of Bark River Tree Service
This past Saturday Boss man (Mike Doering) threw a Christmas party for the crew and friends, he cooked everyone large T-Bone Steaks and Potatoes with all the fixing’s, needless to say it was a good time and everyone enjoyed themselves.
I will keep everyone informed on the happenings here at Bark River Tree Service and until next time Happy New Year.
Ben Costa on Behalf of Bark River Tree Service
Monday, November 23, 2009
Welcome to Bark River Tree Service
Monday, November 23, 2009
Welcome to Bark River Blog
Today was another one of those days, and when I say another one of those days I'm talking about this weather! The rain not only affects our outside work but it makes us tackle the inside projects, one of which was to go through the 25 years of pictures Mike (Bossman at Bark River Tree Service) has accumulated in the tree service industry. There were photos of Mike dumping loads of wood in the old brewers stadium, to pictures of his family growing up and participating in the local Dousman parade. It was kind of like going back in time and watching how his business got to where it is today, from our certified arborist to the mulitiple skiddloaders he has worked many long and honest hours and I for one am glad to work for a boss like that.
Much of our work lately has come from the many diseases and bugs that attack the trees one them being the Oak Wilt, here is everything you could want to know about it.
Identify, Prevent, and Control Oak Wilt
Introduction
Distribution
Hosts
How Infection Occurs: The Disease Cycle of Oak Wilt
Local spread of oak wilt
Long-distance spread of oak wilt
Symptoms
Red oak group
White oak group
Texas live oak
Diagnosis
Other disorders of oaks
Oak Anthracnose
Oak Decline
Twolined Chestnut Borer
Integrated Management of Oak Wilt
1.
Preventing new infection centers
Remove infected trees
Avoid injuring healthy trees
2.
Controlling existing infection centers
Trenching and vibratory plowing
Chemical root disruption
3.
Chemical control using fungicides
Summary of integrated oak wilt management strategies
References
Glossary
Companion Publication
Authors, Illustrations, and Acknowledgments
Northeastern Area State and Private Forestry Offices, North Central Research Station, Forest Service Southern Region State and Private Forestry Offices
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. 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 1980's. Some plant pathologists think that oak wilt is an exotic disease, arriving in North America in the early 1900's, but the fungus has never been reported from any country other than the United States. The disease has also become much more apparent in some local areas since the 1980's 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 Fig. 1.
Figure 1. In 1998, oak wilt was distributed over much of the eastern United States.
Oaks can be organized into three main groups, based on leaf shape: 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 rounded tips (Fig. 2). Oaks 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 can be killed over a period of one to several years. Resistance in white oaks appears to be related to characteristics of physiology and morphology. Upon wounding, infection, or as a part of the natural aging process, white oaks tend to form minute 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, but 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. Texas live oak (Q. virginiana) is moderately susceptible to the disease, but because of its tendency to form large, root-connected clones through which the disease can spread, it is also considered to be an important host. 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).
Figure 2. The three main groups of oaks are organized by leaf shape.
The oak wilt fungus moves from tree to tree in two ways: transported underground through the roots or overland by insect vectors. Local spread of oak wilt Most new tree infections occur as a result of the fungus moving from an infected tree to a nearby healthy tree through connected root systems, a process called "local spread" (Fig. 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 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 root system. Such situations can lead to rapid expansion of oak wilt centers if even one tree in the group becomes infected.
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.
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, a process called "overland spread" (Fig. 3, upper pathway). Under certain moisture and temperature conditions, compact masses of spore-producing fungal material, variously called "spore mats," "spore pads," "pressure mats," or "pressure pads" are sometimes formed on oak trees that have been killed by oak wilt (Fig. 4). These mats form just under the bark, in contact with both the bark and the infected sapwood of the tree. As the mats mature, they produce specialized structures that exert outward pressure on the bark (the "pressure pads") and cause it to split, providing a route for insects to reach the mats (Fig. 5). Oak wilt spore mats emit a strong fruity or wine-like odor that attracts many different species of nitidulid beetles (Fig. 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. The sap attracts insects, including nitidulid beetles that have visited oak wilt spore mats. The overland movement of nitidulid beetles from spore mats on infected trees to wounds on otherwise healthy trees thus creates most new infection centers.
Not all nitidulid beetles are vectors of the oak wilt pathogen. In the North, nitidulids in the genera Carpophilus, Colopterus and Epurea are most often associated with both oak wilt spore mats and fresh wounds on healthy oaks. The common picnic beetle in the genus Glischrochilus (the larger beetle in Fig. 6) has often been implicated in the oak wilt disease cycle, but does not appear to be an important vector of the disease.
Figure 6. Nitidulid beetles are primarily responsible for overland spread of oak wilt.
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 spring of the year after the tree dies, or sometimes in autumn of the year the tree dies. The period of time during which mats are formed increases with decreasing latitude. In Texas, mat formation occurs at any time during the year, but is most common in late fall and winter when the weather is cooler and wetter. Spore mats usually do not form on trees smaller than 6 inches in diameter at breast height, although smaller trees can occasionally support mats. In Texas, spore mats are formed only on Texas red oak and blackjack oak, and never on Texas live oak. For this reason, the red oaks are important for establishing new infection centers in Texas. Another group of insects, oak bark beetles (not pictured), can also carry spores of the oak wilt pathogen and help to create new infection centers. These beetles acquire spores of the fungus while feeding on infected branches, and subsequently transmit them when feeding on healthy trees.
Oak wilt disease symptoms progress differently in red oaks, white oaks, and Texas live oak.Oak wilt is usually identified in red oaks by the symptoms of 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 (Fig. 7B). The progressing discoloration may be interrupted by the leaf veins, as shown in the white oak leaf in Fig. 7A, or may affect the entire upper portion of the leaf, as shown in the red oak leaf in Fig. 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.
Figure 7. Symptoms of oak wilt in A. white oak, B. red oak and C. Texas live oak.
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 oaks usually die slowly, one branch at a time, over a period of one to many years. Wilting and death of leaves on individual branches occur in a similar fashion to the disease in red oaks, but usually progresses much more slowly. 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 (Fig. 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 may be missing.Texas live oaks can wilt and die rapidly or slowly, depending on the timing of infection and weather conditions, but 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 which eventually turn brown ("necrotic"), a symptom termed veinal necrosis (Fig. 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 necessarily the result of oak wilt, and 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.
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 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. These oak disorders may sometimes be confused with oak wilt: anthracnose, decline, and infestation with twolined chestnut borer.Trees in the red or 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 wetfor an extended period during 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 early in 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. 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 over a local or regional area. Symptoms vary greatly, and differentiating oak decline from oak wilt can be quite difficult. The absence of the typical leaf symptoms of oak wilt and the retention of dead leaves on the tree are indicators of oak decline. 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. 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.
Oak wilt can be managed by 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.
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, either by preventing the development of spore mats of the fungus on diseased trees, or by preventing the transfer of fungal spores by beetles to healthy trees. In practice this involves removing dead or diseased trees and avoiding injury to healthy trees.Remove infected treesTrees 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, 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 spread the infection by accelerating the movement of the fungus into adjacent trees that are grafted to it by the roots. To avoid this problem, before removing living diseased trees disrupt interconnected roots as described in the section on "Controlling existing infection centers."Avoid injuring healthy treesTrees with fresh wounds outside existing oak wilt centers are 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 or pruning are unavoidable, or if storms injure oak trees during the critical period, the wounds should be treated immediately with a commercial tree paint or wound dressing. Tree paints are normally not recommended for general use, but in this instance use of these products can protect trees from oak wilt. In the North, if trees are wounded during the dormant season tree paints are not necessary, but judicious use during the rest of the year is acceptable. From Missouri to Texas, tree paint should be used immediately after trees are wounded, at any time of the year.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, causing infection in healthy oaks. Disrupting the connections between 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 reestablished. The fungus that causes oak wilt does not survive in the root systems of dead trees for more than a few years.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 roots of healthy trees. Either 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, timing of 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 plowingCutting roots by using a trenching or cutting tool effectively controls the expansion of oak wilt pockets. In the Lake States, using a vibratory plow with a five-foot blade (Fig. 8) is the most common 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 make the use of a rock saw necessary for disrupting oak roots. A chain trencher, backhoe or ripper bar can sometimes be used. Trench depth should be at least 3 feet, although this may be difficult to achieve. The lines cut by these trenching implements are usually referred to as "barrier lines" (Fig. 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 (Fig. 9).The efficacy of root graft disruption can be enhanced 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 to ensure that all of the oak roots inside the barrier will die before root grafts can be reestablished. 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.Chemical root disruptionBiocidal 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, 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, who has been trained in their use. In addition, these chemicals are costly, may cause damage to the trees, and are effective only in uniform-textured soils where the chemical distribution is even and predictable.Fungicides have been developed that may be effective in preventing oak wilt when injected into living oak trees without active symptoms. These fungicides are apparently unable to stop an already infected oak tree from dying. Those currently available utilize some form of a chemical called propiconazol 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 high-value trees should be considered for treatment. Contact your county extension office for current advice on the use of chemicals for control of oak wilt.
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 dotted lines are secondary barriers.
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, use tree wound dressings or paints 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 vibratory plow line, trench barriers 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, 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 off-site without debarking, chipping, or properly drying it. Do not move or store firewood from infected 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 long-distance transmission of oak wilt.
Appel, D.N. 1994. The potential for a California oak wilt epidemic. Journal of Arboriculture 20: (2) 79-86. Appel, D.N.; Cameron, R.S.; Wilson, A.D; Johnson, J.D. 1995. How to identify and manage oak wilt in Texas. How-to SR-1 USDA Forest Service, Southern Research Station; New Orleans, LA: 7p. French, D.W.; Juzwik, J. 1999 (revised). Oak wilt in Minnesota. Extension publication MI-3174-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. USDA Forest Service, Northeastern Area State and Private Forestry; St. Paul, MN: 12 p.
Anthracnose
A fungal disease of the leaves of many tree species. On oak, this disease may be confused with 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 for controlling 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
Spread of oak wilt by nitidulid beetles from spore mats on infected trees to open wounds on healthy trees. Oak bark beetles can also facilitate the spread of oak wilt.
Nitidulid Beetles
Beetles in the family Nitidulidae, sometimes called sap beetles. These beetles have been implicated as the primary carriers of fungal spores of the oak wilt pathogen to healthy trees.
Necrosis (necrotic)
A brown discoloration of leaves that indicates dead tissue.
Overland Spread
See "long-distance spread."
Pressure Mat, Pressure Pad
See "Spore Mat"
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 to protect 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 to protect 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 in 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.
Vector
An organism, such as an insect, mite, nematode or higher animal such as a bird or rodent that carries 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.
Pokorny, J. 1999. How to Collect Field Samples and Identify the Oak Wilt Fungus in the Laboratory. NA-FR-01-99. USDA Forest Service, Northeastern Area State and Private Forestry; St. Paul, MN: 12 p.
Joseph G. O'Brien, Plant Pathologist
USDA Forest ServiceNortheastern Area State and Private ForestryForest Health Protection
Manfred E. Mielke, Forest Health Specialist
USDA Forest ServiceNortheastern Area State and Private ForestryForest Health Protection
Dale Starkey, Plant Pathologist
USDA Forest ServiceSouthern Region Forest Health Protection
Jennifer Juzwik, Research Plant Pathologist
North Central Research Station
Julie Martinez, Scientific IllustratorMinneapolis, MinnesotaThe 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, for editing the manuscript.
Headquarters Office Northeastern Area State and Private Forestry USDA Forest Service11 Campus Boulevard, Suite 200 Newtown Square, PA 19073
Durham Field Office Northeastern Area State & Private Forestry USDA Forest Service Louis C. Wyman Forest Services Laboratory P.O. Box 640 Durham, NH 03824-0640
Morgantown Field Office Northeastern Area State & Private Forestry USDA Forest Service 180 Canfield Street Morgantown, WV 26505-3101
St. Paul Field Office Northeastern Area State & Private Forestry USDA Forest Service 1992 Folwell Avenue St. Paul, MN 55108-1099
North Central Research Station Forest Service–U.S. Department of Agriculture 1992 Folwell Ave. St. Paul, MN 55108-1099
Headquarters Office USDA Forest ServiceSouthern RegionState & Private ForestryForest Health Protection1720 Peachtree Road, NWRoom 862 SAtlanta, GA 30367-9012
Asheville Field OfficeUSDA Forest ServiceSouthern RegionState & Private ForestryForest Health ProtectionAsheville Field OfficeP.O. Box 2680Asheville, NC 28802
Pineville Field OfficeUSDA Forest ServiceSouthern RegionState & Private ForestryForest Health ProtectionPineville Field Office2500 Shreveport Hwy.Pineville, LA 71360
Welcome to Bark River Blog
Today was another one of those days, and when I say another one of those days I'm talking about this weather! The rain not only affects our outside work but it makes us tackle the inside projects, one of which was to go through the 25 years of pictures Mike (Bossman at Bark River Tree Service) has accumulated in the tree service industry. There were photos of Mike dumping loads of wood in the old brewers stadium, to pictures of his family growing up and participating in the local Dousman parade. It was kind of like going back in time and watching how his business got to where it is today, from our certified arborist to the mulitiple skiddloaders he has worked many long and honest hours and I for one am glad to work for a boss like that.
Much of our work lately has come from the many diseases and bugs that attack the trees one them being the Oak Wilt, here is everything you could want to know about it.
Identify, Prevent, and Control Oak Wilt
Introduction
Distribution
Hosts
How Infection Occurs: The Disease Cycle of Oak Wilt
Local spread of oak wilt
Long-distance spread of oak wilt
Symptoms
Red oak group
White oak group
Texas live oak
Diagnosis
Other disorders of oaks
Oak Anthracnose
Oak Decline
Twolined Chestnut Borer
Integrated Management of Oak Wilt
1.
Preventing new infection centers
Remove infected trees
Avoid injuring healthy trees
2.
Controlling existing infection centers
Trenching and vibratory plowing
Chemical root disruption
3.
Chemical control using fungicides
Summary of integrated oak wilt management strategies
References
Glossary
Companion Publication
Authors, Illustrations, and Acknowledgments
Northeastern Area State and Private Forestry Offices, North Central Research Station, Forest Service Southern Region State and Private Forestry Offices
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. 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 1980's. Some plant pathologists think that oak wilt is an exotic disease, arriving in North America in the early 1900's, but the fungus has never been reported from any country other than the United States. The disease has also become much more apparent in some local areas since the 1980's 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 Fig. 1.
Figure 1. In 1998, oak wilt was distributed over much of the eastern United States.
Oaks can be organized into three main groups, based on leaf shape: 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 rounded tips (Fig. 2). Oaks 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 can be killed over a period of one to several years. Resistance in white oaks appears to be related to characteristics of physiology and morphology. Upon wounding, infection, or as a part of the natural aging process, white oaks tend to form minute 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, but 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. Texas live oak (Q. virginiana) is moderately susceptible to the disease, but because of its tendency to form large, root-connected clones through which the disease can spread, it is also considered to be an important host. 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).
Figure 2. The three main groups of oaks are organized by leaf shape.
The oak wilt fungus moves from tree to tree in two ways: transported underground through the roots or overland by insect vectors. Local spread of oak wilt Most new tree infections occur as a result of the fungus moving from an infected tree to a nearby healthy tree through connected root systems, a process called "local spread" (Fig. 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 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 root system. Such situations can lead to rapid expansion of oak wilt centers if even one tree in the group becomes infected.
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.
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, a process called "overland spread" (Fig. 3, upper pathway). Under certain moisture and temperature conditions, compact masses of spore-producing fungal material, variously called "spore mats," "spore pads," "pressure mats," or "pressure pads" are sometimes formed on oak trees that have been killed by oak wilt (Fig. 4). These mats form just under the bark, in contact with both the bark and the infected sapwood of the tree. As the mats mature, they produce specialized structures that exert outward pressure on the bark (the "pressure pads") and cause it to split, providing a route for insects to reach the mats (Fig. 5). Oak wilt spore mats emit a strong fruity or wine-like odor that attracts many different species of nitidulid beetles (Fig. 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. The sap attracts insects, including nitidulid beetles that have visited oak wilt spore mats. The overland movement of nitidulid beetles from spore mats on infected trees to wounds on otherwise healthy trees thus creates most new infection centers.
Not all nitidulid beetles are vectors of the oak wilt pathogen. In the North, nitidulids in the genera Carpophilus, Colopterus and Epurea are most often associated with both oak wilt spore mats and fresh wounds on healthy oaks. The common picnic beetle in the genus Glischrochilus (the larger beetle in Fig. 6) has often been implicated in the oak wilt disease cycle, but does not appear to be an important vector of the disease.
Figure 6. Nitidulid beetles are primarily responsible for overland spread of oak wilt.
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 spring of the year after the tree dies, or sometimes in autumn of the year the tree dies. The period of time during which mats are formed increases with decreasing latitude. In Texas, mat formation occurs at any time during the year, but is most common in late fall and winter when the weather is cooler and wetter. Spore mats usually do not form on trees smaller than 6 inches in diameter at breast height, although smaller trees can occasionally support mats. In Texas, spore mats are formed only on Texas red oak and blackjack oak, and never on Texas live oak. For this reason, the red oaks are important for establishing new infection centers in Texas. Another group of insects, oak bark beetles (not pictured), can also carry spores of the oak wilt pathogen and help to create new infection centers. These beetles acquire spores of the fungus while feeding on infected branches, and subsequently transmit them when feeding on healthy trees.
Oak wilt disease symptoms progress differently in red oaks, white oaks, and Texas live oak.Oak wilt is usually identified in red oaks by the symptoms of 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 (Fig. 7B). The progressing discoloration may be interrupted by the leaf veins, as shown in the white oak leaf in Fig. 7A, or may affect the entire upper portion of the leaf, as shown in the red oak leaf in Fig. 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.
Figure 7. Symptoms of oak wilt in A. white oak, B. red oak and C. Texas live oak.
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 oaks usually die slowly, one branch at a time, over a period of one to many years. Wilting and death of leaves on individual branches occur in a similar fashion to the disease in red oaks, but usually progresses much more slowly. 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 (Fig. 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 may be missing.Texas live oaks can wilt and die rapidly or slowly, depending on the timing of infection and weather conditions, but 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 which eventually turn brown ("necrotic"), a symptom termed veinal necrosis (Fig. 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 necessarily the result of oak wilt, and 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.
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 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. These oak disorders may sometimes be confused with oak wilt: anthracnose, decline, and infestation with twolined chestnut borer.Trees in the red or 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 wetfor an extended period during 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 early in 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. 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 over a local or regional area. Symptoms vary greatly, and differentiating oak decline from oak wilt can be quite difficult. The absence of the typical leaf symptoms of oak wilt and the retention of dead leaves on the tree are indicators of oak decline. 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. 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.
Oak wilt can be managed by 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.
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, either by preventing the development of spore mats of the fungus on diseased trees, or by preventing the transfer of fungal spores by beetles to healthy trees. In practice this involves removing dead or diseased trees and avoiding injury to healthy trees.Remove infected treesTrees 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, 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 spread the infection by accelerating the movement of the fungus into adjacent trees that are grafted to it by the roots. To avoid this problem, before removing living diseased trees disrupt interconnected roots as described in the section on "Controlling existing infection centers."Avoid injuring healthy treesTrees with fresh wounds outside existing oak wilt centers are 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 or pruning are unavoidable, or if storms injure oak trees during the critical period, the wounds should be treated immediately with a commercial tree paint or wound dressing. Tree paints are normally not recommended for general use, but in this instance use of these products can protect trees from oak wilt. In the North, if trees are wounded during the dormant season tree paints are not necessary, but judicious use during the rest of the year is acceptable. From Missouri to Texas, tree paint should be used immediately after trees are wounded, at any time of the year.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, causing infection in healthy oaks. Disrupting the connections between 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 reestablished. The fungus that causes oak wilt does not survive in the root systems of dead trees for more than a few years.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 roots of healthy trees. Either 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, timing of 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 plowingCutting roots by using a trenching or cutting tool effectively controls the expansion of oak wilt pockets. In the Lake States, using a vibratory plow with a five-foot blade (Fig. 8) is the most common 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 make the use of a rock saw necessary for disrupting oak roots. A chain trencher, backhoe or ripper bar can sometimes be used. Trench depth should be at least 3 feet, although this may be difficult to achieve. The lines cut by these trenching implements are usually referred to as "barrier lines" (Fig. 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 (Fig. 9).The efficacy of root graft disruption can be enhanced 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 to ensure that all of the oak roots inside the barrier will die before root grafts can be reestablished. 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.Chemical root disruptionBiocidal 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, 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, who has been trained in their use. In addition, these chemicals are costly, may cause damage to the trees, and are effective only in uniform-textured soils where the chemical distribution is even and predictable.Fungicides have been developed that may be effective in preventing oak wilt when injected into living oak trees without active symptoms. These fungicides are apparently unable to stop an already infected oak tree from dying. Those currently available utilize some form of a chemical called propiconazol 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 high-value trees should be considered for treatment. Contact your county extension office for current advice on the use of chemicals for control of oak wilt.
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 dotted lines are secondary barriers.
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, use tree wound dressings or paints 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 vibratory plow line, trench barriers 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, 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 off-site without debarking, chipping, or properly drying it. Do not move or store firewood from infected 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 long-distance transmission of oak wilt.
Appel, D.N. 1994. The potential for a California oak wilt epidemic. Journal of Arboriculture 20: (2) 79-86. Appel, D.N.; Cameron, R.S.; Wilson, A.D; Johnson, J.D. 1995. How to identify and manage oak wilt in Texas. How-to SR-1 USDA Forest Service, Southern Research Station; New Orleans, LA: 7p. French, D.W.; Juzwik, J. 1999 (revised). Oak wilt in Minnesota. Extension publication MI-3174-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. USDA Forest Service, Northeastern Area State and Private Forestry; St. Paul, MN: 12 p.
Anthracnose
A fungal disease of the leaves of many tree species. On oak, this disease may be confused with 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 for controlling 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
Spread of oak wilt by nitidulid beetles from spore mats on infected trees to open wounds on healthy trees. Oak bark beetles can also facilitate the spread of oak wilt.
Nitidulid Beetles
Beetles in the family Nitidulidae, sometimes called sap beetles. These beetles have been implicated as the primary carriers of fungal spores of the oak wilt pathogen to healthy trees.
Necrosis (necrotic)
A brown discoloration of leaves that indicates dead tissue.
Overland Spread
See "long-distance spread."
Pressure Mat, Pressure Pad
See "Spore Mat"
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 to protect 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 to protect 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 in 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.
Vector
An organism, such as an insect, mite, nematode or higher animal such as a bird or rodent that carries 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.
Pokorny, J. 1999. How to Collect Field Samples and Identify the Oak Wilt Fungus in the Laboratory. NA-FR-01-99. USDA Forest Service, Northeastern Area State and Private Forestry; St. Paul, MN: 12 p.
Joseph G. O'Brien, Plant Pathologist
USDA Forest ServiceNortheastern Area State and Private ForestryForest Health Protection
Manfred E. Mielke, Forest Health Specialist
USDA Forest ServiceNortheastern Area State and Private ForestryForest Health Protection
Dale Starkey, Plant Pathologist
USDA Forest ServiceSouthern Region Forest Health Protection
Jennifer Juzwik, Research Plant Pathologist
North Central Research Station
Julie Martinez, Scientific IllustratorMinneapolis, MinnesotaThe 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, for editing the manuscript.
Headquarters Office Northeastern Area State and Private Forestry USDA Forest Service11 Campus Boulevard, Suite 200 Newtown Square, PA 19073
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North Central Research Station Forest Service–U.S. Department of Agriculture 1992 Folwell Ave. St. Paul, MN 55108-1099
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