Oak Tree Diseases

Hunt County Master Gardner, Byron Chitwood, writes about Oak Tree Diseases.

I attended an oak wilt training session eleven years ago in Granbury.  One of the first questions the instructor asked me was “why are you attending this training session.  The only trees they have in East Texas are pines”.  I did manage to explain to him that Hunt County was not considered East Texas and that we have very few pine trees and plenty of oak trees.  In the eleven years since the training, I have yet to identify a case of oak wilt in Hunt County.  I hope it stays that way since oak wilt is terminal to whatever tree it infects. There is quite a bit of oak wilt in Dallas and Collin Counties

Oak wilt is a fungus that is carried from an infected tree to another by a small beetle, Nitidulid that feeds on sap from oak trees. If the sap producing tree is infected with oak wilt fungus and a Nitidulid encounters the sap from the tree, it can carry the fungus and infect a healthy tree.  The fungus only survives in mild temperatures.  Therefore, oak trees should only be pruned in the coldest of hottest part of the year.  This would usually be August or February.  Another form of transport of oak wilt fungus is purchasing firewood from an area where the disease exists.  If you purchase firewood from a source other than a local one, be sure that it does not come from a questionable area.  Otherwise, be sure the wood has been seasoned for a year and half.  If the source is questionable, either don’t buy the wood or if you do, stack it away from other trees and cover tightly with a clear plastic cover.  During the summer months, the stacked wood under the cover will heat up and kill any oak wilt spoors plus any other diseases and most insects.

A disease that has been prevalent in Hunt County is Hypoxylon Canker.  This disease is carried by a wind borne spoor from infected trees. Normally, healthy trees are not affected by this disease but this area has been an extended drought for many years which has stressed oak trees to the point that they are susceptible to contacting the disease.  The infecting spoors enter through a crack in the bark or some other wound to the tree.  The fungus thrives under the bark and grows until the bark falls off the trunk of the tree.  This is terminal to the infected tree.  I suspect that we will see quite a bit more of this disease until the drought and the conditions that it has caused are in the past.  It is recommended that trees that have died from this disease be removed and burned.  The spoors will not be transmitted by smoke.

Some manmade conditions that can cause premature tree death are grading around a tree or filling with topsoil under an existing tree.  Also, building a raised flower bed under a tree can cause the tree to die.  The tree with the flower bed might look good for several years but in will more than likely die.  Parking cars or equipment under a tree will compact the soil that covers the roots and can suffocate the tree.

Tree diseases can be difficult to diagnose.  If you have a suspect, call the Texas AgriLife office nearest to you and perhaps a Master Gardener can give you some advice.  Have as much information on the disease of pest that you can gather.  That will help the Master Gardener identify the problem.

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