They may look like cute and furry garden pets, but they really are more of a pest than a pet. Caterpillar pests are common on many landscape and garden plants and can cause mild to severe damage depending on plant species and number of caterpillars present.
If the number of caterpillars is low, gardeners may not even need to bother with trying to control them. Caterpillars have plenty of natural enemies such as parasitic flies and wasps, disease, predator insects and birds who are more than happy to keep the number of caterpillars in check.
Fortunately, a healthy shade tree can withstand a large population of caterpillars and survive, even if there is complete defoliation early in the growing season. New transplants or trees weakened by weather or other factors, will not fare as well and likely will require steps to be taken.
Early detection and removal prevent excessive damage. Look for feeding holes, excrement, webbed or rolled leaves, caterpillars and eggs. Hand-picking caterpillars from flowering plants and vegetables is an effective, but time consuming, method of control.
But, for gardeners wanting to go green, this may be the favored method. Gardeners can squish the larvae or drop them into soapy water to destroy them, or they may choose to locate them to another part of the yard. Caterpillars are unlikely to return to the affected plant as long as they’ve been moved far enough away. Prune off rolled or webbed leaves in trees if you can reach them.
When it comes to using insecticides, choose those more specific to caterpillars so they don’t harm beneficial insects. Most caterpillars are very susceptible to products containing Bacillus thuringiensis subspecies kurstaki, such as Javelin, Dipel or Thuricide. Bacillus thuringiensis subspecies kurstaki is a natural bacteria found in the soil that only kills caterpillars of moths and butterflies.
This product is less effective on older larvae because they must consume it for effective control. Young and older caterpillars also can be controlled with the naturalyte ingredient spinosad that is found in Conserve and some retail insecticide products, as well as other insecticides that are labeled for these pests in ornamentals.
Control is best achieved before caterpillars become full-grown, and it is essential to get thorough coverage, since they are often slightly protected within the leaves or their nest. Of course, it is important to select the right product for the given situation and to always read and follow product labels directions.
Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by the Oklahoma State University Extension is implied.
David Hillock is a consumer horticulturist with OSU cooperative extension.