April 13, 2001
Some oak trees stressed by several summers of hot, dry Arkansas weather are dying, says the Cooperative Extension Service, University of Arkansas. The culprit in some of the deaths is Hypoxylon canker, a disease caused by a fungus that mainly attacks red and black oak species under stress, according to Tamara Walkingstick, an Extension forester.
Walkingstick said the disease never acts alone in killing a tree. She said it is a contributing factor in a tree's death along with stress caused by drought, soil compaction or root damage from construction activities.
“After the bad drought in 1980, we saw a higher incidence of Hypoxylon canker,” she said. “Researchers aren't sure how the disease gets started in a tree. But they do know that it tends to attack weakened or stressed trees.
“These are opportunistic fungi, usually unable to cause disease in a healthy tree, but quick to colonize weakened trees,” Walkingstick said.
Walkingstick said the most obvious symptom of the disease is the sloughing off of bark to expose a white fungus. This is in the later stage of the disease. The fungus apparently enters branches through wounds, grows and causes decay. The first symptoms are yellowing and wilting of leaves and death of top branches.
The fungus spreads by a brownish, dusty mass that is easily blown from tree to tree causing new infections. It changes to white and later to black.
Large trees can be killed within a year or two of being infected. But the fungus can be active in trees for several years before symptoms are noticed.
“Usually, by the time a landowner or homeowner sees the symptoms, the tree is already on it's way out,” Walkingstick said. “It's a fatal disease. There's no cure. The fungus attacks the living layer and girdles, or strangles, the tree.”
She said if you have a dead tree or limbs with this fungus, remove them, because the disease can spread to other trees. The wood can be safely burned in a fireplace.
If you are uncertain if your tree has this disease, you can contact a certified arborist or forester with the Arkansas Forestry Commission and have them come out and look at the tree. You can take a sample of suspected fungus to your county Extension office and ask an agent to have it tested.
If you have to have a tree removed, get several bids and check references of the companies. Make sure the company you hire is licensed and bonded.
You can help prevent the disease by minimizing damage to roots during construction, and by watering and mulching around trees during the summer, according to Walkingstick. “If you prune, make sure you do it properly because this fungus can enter through a wound that's not healing or sealing over well. Most county Extension offices have information on proper pruning techniques,” Walkingstick said.
Lamar James is an Extension Communications Specialist with the University of Arkansas.
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