What is eating my plants?

Is something chewing on and creating holes in your plant leaves, but you can’t find any insects? Does new damage continue to appear?

This is a true case of whodunit. This is a common question, particularly in early summer, and the absence of a pest with continued damage suggests a nocturnal pest or possibly a shot-hole disease (which causes portions of the leaf to fall out).

When shot-hole-type diseases can be ruled out, there are many potential nocturnal pests. Scouting at night can help; visit the landscape in the middle of the night with a flashlight. When night scouting is not possible, careful observation and a little exploration may provide enough clues to determine the culprit.

Snails and slugs require damp and humid conditions and often feed on landscape plants at night, retreating to damp and humid habitats by day. Snails and slugs leave slime trails from excreted mucus. The mucus often dries and glistens on plant leaves or other materials and can be a good indicator of pest activity.

Snails and slugs create irregular holes in the leaves, often with smooth edges. They prefer tender foliage and certainly have preferences for different species of plants, Hosta often being a favorite.

Tattered leaves on lantana from earwig feeding. Photo by Russell Norton.

Another nocturnal pest frequently encountered in early summer is earwigs. Earwigs breed and nest in soil and frequently live in the area between soil and wood, stone or mulch. Earwigs are scavengers and feed on a wide assortment of materials including detritus (decaying organic matter), fungi, insects and live plants.

Earwigs generally feed on tender plant parts, particularly seedlings and in flower or vegetative buds. Earwigs do not leave slime trails, and the feeding damage often looks ragged or torn. Look under pots, edging, pavers or mulch near the damaged plants for the presence of earwig populations.

Other nocturnal insects that may be encountered are cutworms and beetles. Cutworms are caterpillars that feed on young seedlings or transplants at night. They cut the stems and feed on the plant, frequently leaving portions of the plant nearby or half buried. Sift through the soil around recently cut-down seedlings or any remaining plant parts on the ground; the plump caterpillars are typically easily found.

There are also several nocturnal beetles. The most common in our area is the Asiatic beetle. They feed on a wide variety of plants at night, typically in July. Asiatic beetles retreat to the soil or mulch during the day, and like cutworms are typically fairly easy to expose sifting through the soil or mulch near damaged plants.

Check out this fact sheet from UMass Extension for more information on managing earwigs, slugs and snails.

Article courtesy of UMass Extension

Cover photo: Glistening slime trail and slug feeding damage on lupine. Photo by Russell Norton.