Zucchini (Cucurbita pepo) is a summer squash and popular garden plant. While a healthy, pest-free zucchini plant produces five or more cylindrical fruits each growing season, production is adversely affected by the presence of several insects pests, including a variety of worms. The worms are the larvae of moths that overwinter in garden debris or migrate into the garden when warm weather arrives. All the worms can be controlled by using the correct pesticide at the correct time in the growing cycle.
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Identify the worm and damage so you know when to apply the pesticide. Squash vine borers mature inside the plant stem after the egg is laid at the base of the plant by a moth. The worm looks like a 1-inch-long maggot and is white to gray. The base of the plant is damaged where the larvae feeds. Affected plants wilt severely and may suddenly die. Cabbage loopers are small green worms up to 1 inch long that appear anywhere on the plant during the growing season. Damage appears on both leaves and flowers. Cutworms cut the plants at the soil level, usually at night. The variegated cutworm climbs a mature plant to feed. They are usually brown and up to 1 inch long. Pickle worms feed on the flowers and new leaves before entering the fruit of the plant and leaving a pin-sized hole. The worms are 1/2 inch long, thin, almost clear in color, and difficult to see.
Carefully read the label on the container of pesticide containing permethrin. Each type of worm will require a slightly different application rate.
Mix pesticide containing permethrin if necessary, according to directions. Permethrin is most often available as a bait or powder, but is also found in a concentrated liquid form.
Sprinkle permethrin powder or pesticide containing permethrin on and around the base of the plants in the evening after the flowers on the zucchini plant have closed. Most worms are active In the evening after sunset when they are not as easily seen by predators. This is also the time when flowers are closed, so bees are not killed by the permethrin application.
Repeat as necessary according to directions on the pesticide label until control of damaging worms is established.