Grub Worms as Pests on Zucchini Plants

Identification

• All varieties of summer and winter squash, including zucchini, are susceptible to damage from the squash vine borer. The pests appear on the plants during summer and are impossible to control once the wormlike grubs eat their way into the stems. Pumpkin plants are also damaged by the pests.

Description

• The adult squash vine borer resembles a wasp with metallic-green front wings and transparent rear wings with black or brown borders. The wingspan is between 1 to 1 ½ inches and the body is black and orange. The white-bodied larvae or grubs have brown heads and eight pairs of legs, with the first three pairs the true legs and the five other pairs the prolegs. The brown, flat eggs of the pests are about the size of a pencil point.

Damage

• The adults lay their eggs in a cluster on a plant's stem base. As soon as the eggs hatch within 10 days, the grubs or worms eat their way inside the stem, leaving a small hole at the entry site. The pests create tunnels inside the stems as they feed, weakening stems and reducing the flow of nutrients. Infested plants wilt and start to die.

Control

• Taking preventative measures is the best way to control infestation, as the grubs cannot be controlled once they are inside the stem. Use pesticides to control adults around the plants during early June. Early presence of larvae on the plants is a sign of more grubs on the way. Apply insecticides every seven days to control new grubs. Use enough spray to cover the whole canopy. Recommended pesticides include products containing carbaryl, permethrin and bifenthrin.