Question: My oak tree is being eaten by hundreds of orange and black caterpillars. They also are leaving residue all over my deck. How can I get rid of them?
Answer: During this time of year the invading caterpillar is the orange-striped oakworm. In certain years, these caterpillars can be very abundant on oaks in late August and September.
These caterpillars can be found throughout eastern United States. In large numbers they are ravenous feeders and can quickly defoliate a tree.
As the caterpillars mature they are often seen crawling across roads, patios, sidewalks and yards. This insect is usually more troublesome because of the large amount of excrement produced.
A group of young larvae begin by skeletonizing a leaf, then later consuming all but the main veins of a leaf, finishing off a branch completely before moving on to the next branch. If you look into your oak trees now you may see them beginning to feed on the leaves.
The orange-striped oakworm moth emerges in June and July and deposits its eggs in clusters of several hundreds on the underside of oak leaves.
The eggs hatch in approximately one week, and tiny green caterpillars emerge. These green caterpillars grow into black ones with yellow or orange stripes running lengthwise along their bodies. Small trees are sometimes completely defoliated by mid-summer.
They may travel a considerable distance searching for an area to pupate. They then will dig into the soil, 3 to 4 inches down, and pupate over the winter.
There is one generation per year and control measures are usually not necessary.
The trees have finished growing for the year, and little damage occurs to the health of the tree. If however, control measures are warranted, such as to protect a small seedling oak or a high value tree, or they're just plain old driving you crazy, you may want to spray your trees by mid-August.
By the time defoliation becomes apparent, the caterpillars are fully grown, harder to kill and almost through feeding. Bacillus thuringiensis (Bt), Sevin or Orthene are effective means of control.
On big trees, you will need to hire a tree service, which has the equipment to spray the entire tree.
However, if your neighbor hasn't sprayed his trees, they may move on to yours as soon as they are finished with your neighbor's trees.
Remember, they are more of a nuisance than a threat to the health of your tree.
Mona Bawgus is a certified master gardener and consumer horticulturist with Rutgers Cooperative Extension of Atlantic County. Write to her c/o Rutgers Cooperative Exten-sion, 6260 Old Harding Highway, Mays Landing, NJ 08330. Email: