Darrell Blackwelder: Mighty oaks seem to be under attack

Published 12:00 am Friday, June 19, 2015

The relatively mild weather a few weeks before has now evolved into unseasonably hot weather that few people, and plants, for that matter, can tolerate.

With the abrupt change homeowners have many questions about their gardens and landscapes. Heat is an issue in itself that seems to exacerbate problems associated with insects and disease.

Tree problems are by far the most prevalent questions this past week. For some reason, most of the calls concerned oak trees. Because shade and other flowering trees are generally the focal point in a landscape, homeowners become quite concerned when a potential problem occurs.

Below are a few questions posed to Cooperative Extension over the past days.

Question: I have a very large white oak tree that has been oozing sap near the base of the tree for the past few days. Insects and even hummingbirds seem to be attracted and swarming around the tree. Is our tree in danger? What is causing the problem and should I spray to control the insects?

Answer: The problem that is occurring with your oak tree is commonly called “slime flux” or wet wood. It’s a fairly common problem on mature oaks and other trees that is usually initiated by an abrupt change in weather as we’ve experienced over the past few days. It is not a serious problem if your tree is otherwise healthy. Wet wood is caused when bacteria invade a wound, injury or natural opening in the bark. The fermenting wet wood-causing bacteria produce a gas which pressurizes tree fluids in the wood under the bark. When enough pressure is created, the gas causes the wet wood liquid to ooze, flux or bubble through the bark. Many different types of microorganisms thrive in the flux, producing a fermenting foul or alcoholic smell. Various types of insects such as bees, wasps and even hummingbirds are attracted to the slime flux. Slime flux may last 2-4 months before it ceases its flow. You may want to go to the website http://www.ces.ncsu.edu/depts/pp/notes/oldnotes/od8.html for more detailed information about slime flux.

Question: I have an oak tree that I noticed had little brown bumps all along the twigs and branches. At first I thought it may be acorns trying to form. Then, I noticed these were sticky insects. Can you tell me what these are? Can I spray to control them?

Answer: The twigs are infested with scale insects. Scales generally weaken the tree but will not kill the tree. Smaller trees can be sprayed with horticultural oils and insecticides. However, if you have a large tree, spraying insecticides will not be beneficial for the health of the tree.

 Question: My oak tree has spots and the leaves are falling. What is this? Will it kill the tree?

Answer: Your oak probably has oak leaf blister. It’s a fungal disease and most oak species are susceptible. The fungus is rarely severe enough to require control measures. Go to http://www.clemson.edu/extension/hgic/pests/plant_pests/trees/hgic2006.html for more detailed information on oak leaf blister.