Posts Tagged ‘fungus’

Last month’s article covered basic information about Oak Wilt and its symptoms, along with an introduction to its transmission. The article noted that there is much confusion and misinformation regarding Oak Wilt, and research goes only so far in providing the answers to important questions. Future research will likely change current recommendations — which is a good thing. Early detection and an accurate diagnosis, paired with a solid management plan, are critical to managing the disease successfully. In some cases, there may be a need to develop a management plan for an entire city block or particular part of a community.

Oak Wilt Management/Diagnosis

An Oak Wilt diagnosis can be confirmed in a laboratory by isolating the fungus from diseased tissues. Taking tissue samples is not a simple process and should be left to someone with specific training and experience. Each step of the process must be done properly. Although all the symptoms indicate Oak Wilt is present, lab reports may return as a “negative.” A negative from the lab does not mean the sampled tree is not infected, only that the fungus could not be found in the particular sample provided. Note that “someone with specific training and experience” is typically a consulting arborist, but may also be a forester or Oak Wilt researcher.

Oak Wilt Management/Suppression

Fungal Spore Mat

As previously noted, fungal spore mats form only on species in the Red Oak group and produce a fruity odor that attracts the Nitidulid beetle — believed to be responsible for the overland spread of the disease. As a result, infected and dying red oaks are a greater concern, due to the potential for aiding in the overland spread. There is no evidence that live oaks contribute to the overland spread. The firewood and stumps from removed live oak trees are not a concern.

Since the spore mats have been known to form on stumps and firewood of species in the Red Oak group, infected trees should be promptly removed from the site and chipped, burned or buried. If this is not practical, remove the infected tree’s bark from the soil line up to 2 or 3 feet to help prevent the formation of spore mats. In urban areas, grinding the stump below the soil surface is also recommended.

Avoid storing infected red oak firewood near healthy trees unless it is “seasoned” or completely dried for at least one year. If infected red oak wood must be left on a site, it should be covered with clear plastic and the edges buried in the soil. Avoid purchasing red oak firewood that appears green and not ready to burn. However, burning infected oak firewood of any species will not spread the disease since the heat of the fire will destroy fungal spores.

The disease is most often spread by root-to-root contact. In a dense group of live oaks, Oak Wilt can expand outward to 75 feet or more each year. Trenching between infected and non-infected trees is a method of suppression in a rural setting, but it is difficult and less successful in an urban area due to the number of underground utilities and obstructions.

By comparison, Oak Wilt centers in the DFW area do not appear to be expanding outward as rapidly as centers found in Austin. One theory is that the disease expands more rapidly in communities with indigenous populations of red oak and live oak. These populations have root systems that are more interconnected than an urban forest established primarily by planting new trees. One of the primary indigenous oaks in North Central Texas is post oak (Quercus stellata), which is extremely tolerant of the disease. The same is true for chinquapin oak (Quercus muehlenbergii) and bur oak(Quercus macrocarpa), which should be planted more often for this reason. Are you starting to lose some of your fears yet?

Next month`s article will cover Oak Wilt Management/Pruning. The final article will address Prevention and Treatment. Afterward, we hope to have fewer nervous tree mothers!!

About the author: Steve Houser is a Dallas native with more than 30 years of experience as a consulting arborist. He is the president of Arborilogical Services Inc., “The Experts Your Trees Deserve.”  www.arborilogical.com.

Oak Wilt is a complex disease. To fully explain its impact on our trees will require several consecutive articles. Conflicting information in public venues adds to the current Oak Wilt confusion and creates anxiety or anger over the potential loss of a favorite tree. If Grandpa planted the tree, or it screens the neighbors or reduces your energy bill, the tree has special value. It is no longer just a renewable resource easily replaced. Best not to mess with a Texan’s trees!

Although Oak Wilt research is somewhat limited, a good understanding of what is known offers some level of comfort. Dr. David Appel, professor of plant pathology and microbiology at Texas A&M University, is recognized as an expert on the subject. His research has been peer reviewed, and his guidance helped to develop the standards covered in this article, along with the help of two other plant pathologists with extensive Oak Wilt experience. The disease is not rampant or terrorizing all our neighborhoods. It was first discovered in the DFW area in 1978. Let’s keep things in perspective and rely on those who have worked with, managed, and tracked the spread of the disease as a career.

Oak Wilt and Its Symptoms

Oak Wilt is a vascular wilt disease of oak trees caused by the fungus Ceratocystis fagacearum. The fungus enters the tree and stops the flow of water as well as elements by plugging the vessels in the vascular system. All species of oaks are susceptible, with some species being somewhat tolerant. Red oaks, both Shumard and Spanish, are highly susceptible to the pathogen. Live oaks (Quercus fusiformis and Quercus virginiana) follow as a close second. Oaks in the white oak family such as bur oak (Quercus macrocarpa) or chinquapin oak (Quercus muehlenbergii), are more tolerant of an infection.

In the red oak family, the disease expresses itself in two primary ways. The first symptom is an oily green appearance in sections of the tree’s canopy, which rapidly turns a tan or red color. The second, and less common, expression is a heavy and rapid shedding of foliage with individual leaves displaying the symptoms previously mentioned. Infected red oaks typically die within a few months of infection.

Infected live oaks display a variety of foliar symptoms. The most common is called veinal necrosis, a yellowing/browning of the leaf midrib and side veins.

Affected foliage usually drops as this symptom appears, but it is common for some foliage to remain on the tree. Defoliation of live oak trees can occur at any time of the year, but should not be confused with the normal process of leaf-drop and flowering that generally occurs in February and March. Live oaks typically die within six months of infection, with some individuals not dying for years. Advanced training is required to accurately diagnose and properly treat the disease. Uneducated advice can be very costly.

Oak Wilt Transmission

Oak Wilt most frequently spreads from tree to tree by root-to-root contact. Live oaks regularly form functional root grafts with other live oaks. Red oaks appear to form these grafts as well. Oaks like to be “hooked-up” with each other and swap spit. Kidding aside, once the pathogen has entered one tree, it has the potential to move from tree to tree quite readily and efficiently. Root grafting is known to occur between live oaks and red oaks. This phenomenon is not common, but research indicates the potential exists.

Although infrequent, a second method of disease transmission is by overland spread. This occurs when fungal spore mats are produced on a dying red oak and visited by the suspected insect vector or transmitter, the sap-feeding nitidulid beetle. The beetle can carry the spores to a wound on a nearby tree but the spores can infect the tree only if the wound is fresh and created in the previous 24 to 48 hours. All oaks, including live oaks and species in the red oak family, can be infected by overland spread or root-to-root contact.

It should be noted that fungal mats are produced primarily in the spring or cooler times of the year, and only on infected red oaks in a particular stage of decline. Fungal mats are viable, that is producing spores, for a short period — usually two to three weeks at most. Although new infection centers do form, it is not fully understood whether it is from the insect spreading the disease or other methods of transmission not yet discovered or researched.

If you have questions, remember there is more to follow next month on this thrilling subject!

About the author: Steve Houser is a Dallas native with more than 30 years of experience as a consulting arborist. He is the president of Arborilogical Services Inc., “The Experts Your Trees Deserve.” www.arborilogical.com.

Oak wilt is caused by a fungus (Ceratocystis fagacearum) which colonizes the vascular system of the tree.  Conduction of water is disrupted causing the leaves to wilt and ultimately for the tree to die.  The disease is highly virulent and spreads in two (2) known ways.  Trees which have formed root grafts with infected trees may themselves become infected through root graft transmission.  For this reason entire stands of Oak forests may be destroyed over a period of time.  New Oak wilt infection centers may begin when a small sap feeding beetle (aka Nitidulid) visits a spore mat on an infected Red Oak.  (Live Oaks do not produce spore mats).  Once the insect has visited a spore mat, his body may carry the fungal spores to a fresh wound, thus creating a new Oak wilt center infection.  The sap feeding beetles are attracted to feed on the sap which oozes from fresh wounds on trees.  Sap feeding beetle activity, spore formation and tree susceptibility are all at high levels from February to June.  For these reasons the Oak wilt control strategy involves the following recommendations:

1. Avoid pruning mid February – mid June (Red Oaks and Live Oaks).
2. If you must prune during this time, paint cuts and wounds as soon as possible after they occur.  The sap flow from wounds usually has stopped within 24-48 hours, therefore, old wounds do not require painting.
3. Healthy trees near Oak wilt infection centers may be treated on a preventable basis with the fungicide “Propaconizol” (aka Alamo).  This fungicide is injected into the tree at the root flares, and can protect trees for up to three (3) years.
4. Once trees have become infected, successful therapeutic treatment with Alamo is possible, however, results vary and most trees will not survive once symptoms develop.
5. Infected trees, particularly Red Oaks, should be removed promptly.  Red Oak firewood may be another means by which the fungus may be transported to new areas.

Additional research is needed to solve the biology regarding the overland transmission of this potentially devastating tree disease.

More information is available concerning Oak wilt through the Texas A&M extension service, the Texas Forest Service

If you have any further questions or suspect you may have Oak wilt please give us a call or fill out a QUICK contact form!

Oak Anthracnose – introduction.

Oak Anthracnose

Perhaps you have noticed your Live Oaks dropping new leaves this spring. The moist conditions of the past winter and early spring, in conjunction with seasonably cool temperatures, has allowed a number of fungal diseases to develop on the leaves of many of our shade trees. One of these more pre

valent this year is Oak Anthracnose. This disease infects the foliage of nearly all Oak species. It is most prevalent in our Live Oaks this year. Although it can cause problems, generally this disease is not a serious threat to the long-term health of the tree.

Oak Anthracnose – symptoms, characteristics and effects.

The spores of the fungus infect young supple leaves just emerging in the spring. After a period of rapid infection, the leaves begin to fall. Symptoms are evident on a portion of the leaf and are expressed by the margin of the new leaf turning brown or becoming necrotic. This area of browning is usually along one of the leaf margins, causing the leaf to become curled and fall to the ground. Not all infected leaves fall. In fact, many will remain on the tree throughout the season causing the overall appearance of the tree to look a bit odd. Trees in areas of little air movement and those with thick, dense foliage are most readily infected. The lower, inside canopy usually exhibits the most intense symptoms, as these leaves dry more slowly.

Temperatures consistently over 80-85 degrees Fahrenheit cause the infection cycle to cease. Fortunately, the portions of the canopy that drop leaves, will produce new leaves. Single year infections rarely cause much damage to the tree. If the disease repeats next season and infects a larger portion of the tree, preventative fungicide applications may be needed. Foliar sprays, which reduce the incidence of the disease, should begin when the new leaves appear in March. It usually requires 2-3 applications at 21-30 day intervals to adequately manage this disease. If evidence of the disease is observed in late spring or early summer, foliar sprays are normally not recommended. Your arborist may however, recommend deep root fertilization in order to encourage the production of new leaves and improve the overall health and vigor of the tree.

Of course, if you have any further questions regarding Oak Anthracnose, Live Oaks, or trees in general, we are here for you.