Copy 7 oak wilt: cause, prevention and treatments

Beetles carry fungal spores to cuts or wounds on the oak tree

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2. Beetles carry fungal spores to cuts or wounds on the oak tree

If one tree in a large group of healthy trees gets oak wilt, it was probably caused by insect transmission, or use of tools, such as pruners or pruning saws, contaminated with spores from a tree infected with oak wilt.

If a red oak (such as a Spanish or blackjack oak) contracts oak wilt, and the conditions are favorable (the necessary moisture and temperature), the fungus can form fungal mats on the wood of the red oak. The oak wilt fungus can be likened a mushroom, and the spores formed by the fungal mat can be likened to seeds. The fungal mat forms between the bark and the wood. The fungal mat is loaded with spores and has a strong odor of fermenting fruit, which is attractive to tiny sap beetles (only 2 - 3 mm in length). You are unlikely to see either a fungal mat, which is mostly under the bark with only a crack in the bark above it, or a sap beetle. You can smell fungal mats in the woods, especially in the Spring. The sap beetles feed on the fungal mats and get spores stuck to their bodies. The sap beetles then fly around looking for fresh wounds on trees for more sap to eat. If a beetle carrying a spore feeds on a fresh wound on an oak, the spore can germinate and the fungus colonizes the tree. If the tree is a live oak, having interconnected roots, the fungus will reach all of the trees eventually. If it is a red oak, the entire fungal mat cycle begins again. This is clearly undesirable.
Fungal mats are generally formed in the Spring of the year (February, March and April). Sap beetles can be active during the Spring, depending on the temperature. Do not wound or prune your trees during the Spring (February through June in Hill Country). Spring is the most dangerous time of the year for oak wilt, the time when you are most likely to start a new infection. By the Summer, the fungal mats are dried up and gone, BUT the little sap beetles may still be carrying spores around so you still need to paint wounds immediately. Winter, when it is really cold, is a good time to do major pruning on oaks since the beetles are not likely to be flying around. Pruning should be done in the windows when you don’t have all three of the ingredients necessary to contract oak wilt:

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