The extension office has received several calls in the past week from people concerned about insects munching on their oak trees. Most complain of finding large parts of their oak trees rapidly defoliated, with nothing but the midrib of the leaves remaining. This time of year, the damage is most likely caused by the caterpillar stage of an insect called the orange-striped oakworm.
Orange-striped oakworms mainly feed on oak species, but may also infest other species, such as hickory and birch. They normally show up in Georgia between August and September. The larval caterpillar stage is what causes the defoliation on oak trees.
Caterpillars are fairly easy to spot and identify. They are normally 1.5 to 2 inches long, and have black bodies with several orange/yellow stripes running down their backs. They also have a pair of black spines behind their heads and several pairs of smaller spines on their other body segments.
Orange-striped oakworm damage is usually limited to a short time during the late summer. They normally only have one generation per year. After much feeding, the caterpillars change into the pupal stage, which overwinters in the soil underneath trees. Adult moths emerge the following summer, and are reddish-brown with a single white dot on each wing. Adults mate shortly thereafter, and females deposit their eggs on the undersides of oak leaves. Caterpillars emerge and begin the defoliation cycle again.
Although most homeowners are shocked when they first see the damage, orange-stripe oakworms are a native pest and usually do not cause long-term damage. The oaks and the oakworms have lived together for a long time, and even if a severe defoliation occurs, a mature oak tree can usually survive an infestation just fine.
If you have young oak trees that you would like to protect from orange-striped oakworm defoliation, and you can reach them with a wand sprayer, then there are some control options. Products made from the bacteria Bacillus thuriengensis (abbreviated “B.t.”) can be applied to intact foliage, and are a good biological control option. These products, which can be found under brand names such as Thuricide and Dipel, are only harmful to caterpillars, and will not harm other insects or predators.
Synthetic insecticides, such as cyfluthrin or carbaryl, can also be used to control large caterpillar populations.
Don’t be too concerned about larger oak trees, as the oakworm infestation time will be relatively short, and there might be enough time for the trees to grow some new leaves before cold weather sets in.
For more information, please contact the Dawson County Extension office at (706) 265-2442.