- Arkansas trees being attacked by variable oakleaf caterpillar.
- Trees shutting down leaves to conserve water in response to drought.
Across Arkansas, Cooperative Extension Service offices are being called by worried homeowners wondering “what’s wrong with my trees?”
Some common questions with answers from Extension specialists:
- What’s eating my trees?
“Beginning around June 12, I have been getting calls about caterpillars feeding heavily and causing some degree of defoliation in oak trees. Calls have come from as far to the northwest as Benton County and as far to the southeast as Jefferson County with many counties in the river valley along I-40 also reporting damage. The culprit is the variable oakleaf caterpillar, Heterocampa manteo. While we have experienced outbreaks of this forest foliage feeder in the past, this year’s outbreak appears to be more widespread.” --John Hopkins, Extension entomologist for the University of Arkansas System Division of Agriculture.
- I can hear sounds like quiet sprinkles of water, yet it's not raining. Assume the sound is the caterpillars eating?
“When witnessing an infestation, people hear what they describe as caterpillars eating the leaves or what sounds like light rain falling. This sound is in fact, frass, pellet-like caterpillar excrement, dropping onto leaves. The frass should not be allowed to fall on valued items as staining may occur.” -- John Hopkins.
- What can I do to control these caterpillars?
“Chemical control is generally neither necessary nor recommended over large areas. However, localized treatments using pesticides may be necessary to protect high-value trees in residential or recreation areas. Recommended caterpillar control materials may be found in the Shrub and Tree Insect Control Section of MP144, ‘Insecticide Recommendations for Arkansas.’” (see here) --John Hopkins.
- What about the impact of the drought AND the caterpillars?
“Here in the South, the larvae usually emerge in May and feed until late June or early July. This year the defoliation seems to be happening a little early. The last three summers have been extremely dry which means that trees are already stressed. I would suspect that the cumulative effects of the past three summers’ drought coupled with early defoliation might result in a higher mortality rate than normal.” – Tamara Walkingstick, associate director, Arkansas Forest Resources Center.
- How can I keep my tree healthy?
“Homeowners who are already watering the lawn are essentially watering their trees. Trees are very effective in finding moisture. Homeowners need to remember that a large, mature tree can absorb 250 gallons of water a day: that's the equivalent of six bathtubs of water a day for every tree, so it's impractical to water mature trees. If you have smaller trees that were planted more recently, then you should go ahead and water. You can also mulch your trees to conserve soil moisture.” – Tamara Walkingstick.
- Will fertilizer help my tree?
“Never fertilize a tree during drought periods. Most fertilizers are high in nitrogen that promotes foliage growth. If the tree cannot find enough water, then the last thing it needs to do is put on more leaves to support.” – Tamara Walkingstick.
- Why are the leaves changing color?
“As the drought conditions worsen across Arkansas, more and more trees seem to be changing color early. Trees have a series of strategies for reacting to drought. Once the tree senses that there is less water available to the roots, it tries to adapt by increasing root production and using food storage reserves. As the drought lingers, a tree will close down root activities and shed leaves.
“The change in color is a result of the tree simply shutting down photosynthesis or leaf activity. Leaf drop is one of the more harmful responses to drought because it loses its means of producing food. It’s a way for the tree to conserve energy. If moisture becomes available later on this growing season, some trees defoliated by drought may produce another set of leaves. However, this can further stress the tree. It takes a lot of energy to produce leaves and if the tree has already used its food storage reserves, a new set of leaves could cause more damage.” – Tamara Walkingstick.
For more information on trees and pests, contact your county Extension office or visit www.uaex.edu.