ASK THE HORT AGENT

Question What kind of worm is eating the leaves off my trees?

Answer There are lots of caterpillars (or worms) that eat leaves off trees and shrubs. To get a specific answer, you have to ask a more specific question.

In order to determine the exact name of a caterpillar some details are necessary. The best means of identification is a few close up pictures of the culprit. While this is obvious, it may not be possible if they are feeding 30 feet over your head.

Caterpillars have distinct habits and characteristics which make it easy to tell them apart. What type of tree are they in? Some trees have only one specific wormy pest. Catalpa trees have catalpa worms. Other trees may have many types of caterpillars munching away. For example, oak trees have several specific caterpillars. With names like pink-striped, yellownecked and orange-striped, the oakworms’ names sound like holdovers from the 1970s. Oaks may also have caterpillars that feed on other types of trees, like the forest and eastern tent caterpillars.

Next, it is important to know when the caterpillars started eating. Some emerge in spring and some in late summer. There are caterpillars that only emerge one time per year and other caterpillars that have 2 or 3 generations per growing season.

Unfortunately, most people don’t realize they have a pest until many leaves are gone and the worms are nearly grown. Therefore, most folks have no idea when the caterpillars first started eating. Knowing when the worms hatched helps with identification and management.

As a general rule for trees, caterpillars which emerge in spring and only have one generation per year are the most devastating. Bagworms and forest tent caterpillars are two of the most damaging. Bagworms can be deadly in landscape scenarios. Forest tent caterpillars can defoliate full grown trees, but typically don’t kill the host trees. By keeping the leaves eat off, forest tent caterpillars can reduce the diameter growth of certain trees by 75% per year, but at least the trees are still alive.

Some caterpillars can even be identified by where they start feeding, whether they make a protective silk tent and where they congregate at night or cool days.

Once a tremendous amount of detective work has been done, the specific name of the crawly leaf cruncher will pop out. All attention then turns to management, which is the same for all caterpillars. One of two routes can be taken. Either apply a chemical control when they are very little or stand there and wonder “what kind of worm is eating the leaves off my trees?”

For more info on caterpillar pests, visit http://www.ces.ncsu.edu/depts/ent/notes/O&T/shrubs/note07/note07.html If you do not have internet access or you have outdoor grass questions, call me at 910-893-7533 or email me at gpierce@harnett.org

The stinging caterpillars are fairly easy to identify. Their distinguishing characteristic is a “stinging” sensation when you touch them. They also have cool names like Hag moth, Puss caterpillar and Buck moth.

Gary L. Pierce

Horticulture Extension Agent

Harnett County