I hate pickleworms for attempting to ruin my summer squash! They slip into my zucchini, pattypan and straight-neck squash unawares until I see the telltale hole and frass. Cut open, the squash is generally hollowed out and full of caterpillars and caterpillar droppings — yuck! Pickleworms are a common pest on summer squash, winter squash, cucumbers, cantaloupe and pumpkins. They especially like and favor summer squash. However, there are ways to suppress the damage using tried and true integrated pest management principles.
The pickleworm is the caterpillar of a small moth. The adult moth is yellow with brown-bordered wings and a brush-tipped abdomen — not a bad-looking moth. This female moth is only active at night when the eggs are laid on buds and flowers. The larva hatch in four days and tunnel into the developing fruit. Female moths can lay up to 400 eggs, so their capacity to infest your small, backyard crop is great. The young larva are light in color with black spots and gradually turn different colors — white to bronze — depending on what they are feeding on. After 14 days of feeding they are ready to pupate and the cycle continues.
As far as control is concerned, let’s look at natural enemies first. A number of beetles including ground and soldier beetles are predators of the pickleworm. Believe it or not, to their credit, red imported fire ants take a number of pickleworms. Many small parasitic wasps also take a share. Beneficial nematodes have even been used to kill pickleworms before they get into the fruit. While you might consider Bacillus thuringiensis (Bt) for control purposes, as most of the feeding goes on inside the fruit, this microbial insecticide may not ever reach the pickleworm. One cultural practice that does warrant some attention is covering the plants with a floating row cover at night to keep the moths off when they try to lay eggs. The cover goes on at night, but must come off in the morning so that during the day pollinators can get to the flowers. Planting early before pickleworms become a problem can also help reduce the pest pressure — this method has helped me. Keep in mind that there may be natural hosts of pickleworm infestations nearby. Pickleworms feed on wild members of the cucumber family as well including the creeping cucumber.
The insidious cryptic nature of pickleworms can make for a disappointing squash and cucumber crop; however, once you know the biology of this pest, like many others, suppression and success are at hand!
For more information on taking care of many vegetable pests, contact your local County Extension Office.