James City County/Williamsburg
The Master Gardener Program
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Pickleworm, Diaphania nitidalis
There is a 3⁄4-1" light yellow/green worm on my cucumbers, what can I do about them?
Pickle worm is a common problem on squash, cucumbers and muskmelons. You can spray them with an insecticide. Begin treating plants with a registered insecticide at first sign of worms in blossoms and buds; worms must be killed before they enter the fruits.
The pickleworm moth is about 1/2 inch long (see right), with a wingspan of approximately 1 inch. The body and wings are a yellowish brown color with a purplish sheen, and the wings have a broad, light brown border. The tip of the abdomen contains dark, brush like hairs that are waved in the air when the moth is resting. The closely related melon worm moth is similar in appearance, but the wings are predominantly silvery or pearly white in color. Pickleworm moths fly mostly between dusk and early morning and are not usually seen in fields during the day. Female moths lay eggs on leaf and flower buds, leaves, stalks, and young fruit.
Young pickleworm larvae are a pale (see photo), yellowish green with black spots; older larvae are yellowish green or coppery without spots and a brown head. Mature larvae are about 3/4 inch long. Larvae go through five growth stages before pupation and metamorphosis into adult moths.
Life Cycle and Habits:
These insects over winter in semi-tropical areas such as southern Florida. Therefore, infestations depend upon flights of moths from the South. The first pickleworms of the summer usually appear any time from mid-June to mid-August (usually early July in most years). By August the number is increased and they continue to increase until low temperatures kill plants, insects, or both. There are two full generations of pickleworms, with a partial third, if food is available and there is no early frost. Of interest also is that survival of all stages of the pickleworm declines at temperatures above 85 degrees F. The adult is an active night-flying moth that is seldom observed. Moths reared in cages spend most of their time during the day resting on the walls of the cages with their hind wings partly exposed and the tips of the front wings touching the walls. The tip of the abdomen bears a tuft of long hairlike scales. It is held aloft and waved slowly in a circular movement. This gives the impression that it is the creature's head bearing a shaggy mane.
The pickleworm is one of the most damaging insect pests of cucurbits in the western hemisphere. In the United States, pickleworm problems are most severe in the South Atlantic and Gulf Coast states because the pickleworm does not over winter in latitudes north of southern Florida. However, adult moths from over wintering populations in the south migrate northward and have been found as far north as Connecticut. Because pickleworm is a migratory species, greater infestations are found in later-planted cucurbits in the more northern states, and early plantings may escape damage. Pickleworm development is mostly restricted to cucurbit crops (that is, squash, cucumber, zucchini, and melons) and to weeds in the cucurbit family.
Pickleworm may damage summer and winter squash, cucumber, cantaloupe, and pumpkin. Watermelon is an unusual host. The blossom is a favored feeding site, especially for young larvae. In plants with large blossoms, such as summer squash, larvae may complete their development without entering fruit. They may also move from blossom to blossom, feeding and destroying the plant's capacity to produce fruit. Very often, however, the larva burrows into the fruit. The larva's entrance is marked by a small hole, through which frass is extruded. The presence of the insect makes fruit unmarketable, and fungal or bacterial diseases often develop once entry has occurred. When all blossoms and fruit have been destroyed, larvae will attack the vines, especially the apical meristem. Cantaloupe is not a preferred host, and larvae often seem reluctant to burrow into the fruit. Rather, they feed on the surface or "rind", causing scars. Thus, pickleworm is sometimes referred to as "rindworm," though their feeding is not restricted to the surface and they sometimes burrow into the fruit.