Insect leaf damage

Caterpillar

Q. I’ve noticed many leaves of my plants look chewed. What is causing this and is there anything I can spray to help my plants? 

 A. At this time of year, many different types of insects and their larvae frequently feed on the leaves of plants. Without seeing the culprit, it is not possible to determine which insect is causing the damage to your plants. Inspect your plants thoroughly in order to positively identify the insect causing the damage.

Hand removal is recommended by the University of Illinois Extension and is the most environmentally sound method of dealing with insect problems. Applying chemicals without identifying the cause is problematic because gardeners run the risk of killing beneficial insects as well as honeybees or caterpillars that might grow into desirable butterflies or moths. Populations of beneficial insects take longer to rebound following broadcast chemical applications. The repeated use of chemical sprays can actually increase populations of some unwanted insects, such as mites and aphids, while beneficial predator insects may be destroyed.

Most insecticides work by contact and will not be effective if the insect is not present. Birds, spiders, and lacewing bugs feed on caterpillars. Most caterpillars and other pupae are short-term visitors. When larvae pupate to the next stage of their life cycle, injury to the plants will cease and your plants will usually outgrow the damage. We encourage gardeners to adopt environmentally sound practices when dealing with insect problems, and determine your personal threshold for damage.

Chemical treatments should always be considered a last option. Regular monitoring of plants is an important step to determine when and if chemical treatment may be needed. Unusually high populations of damaging insects that threaten the lives of your plants may warrant treatment. When using chemical insecticides, it is important to apply when the least amount of beneficial insects are present. Spot treatment is less damaging to surrounding plants, beneficial insects, pets, and people. Please contact Plant Information Service for the most current chemical options from the University of Illinois Extension.