Posts Tagged ‘fungus’

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 or on the internet at:  http://Cygnus.tamu.edu/texlab/oakwilt.html

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!

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

Oak Anthracnose

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.

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.