QUESTION: The leaves on some of my squash plants are beginning to wilt. Some of the small squash are rotting. What’s the reason?
“When squash leaves wilt and collapse, the squash bug is usually the pest to blame,” says extension agent David Cook. Squash bugs lay small, bronze-colored eggs on the undersides and upper surfaces of the leaves. Nymphs are gray with black legs, and are usually found in groups; adult squash bugs are broad and flat. They pierce the leaves and remove the sap, leaving the leaves wilted. You may also find them on cucumbers, melons and pumpkins.
The best control method is to be on the lookout for the eggs early in the season, and remove any that you find on the plants. (Organic Gardening magazine’s online pest control center suggests gently squishing them before they have a chance to hatch, and squishing any nymphs you may find, as
well.) If you feel you must spray something, Cook says insecticides labeled for squash bug include bifenthrin, or permethrin. Always read and follow label directions.
If a long branch of the plant — or the entire plant — wilts suddenly, it’s the work of the squash vine borer, the larva of a moth that lays her eggs on the leaf stalks and vines. The eggs hatch in about a week, and the larva bores into the stem of the plant and begins to feed. If you look closely, you may find sawdust-like material near the base of the plant. To try to save the vine, split the stem open and remove the caterpillar. Mound soil up around the wound to encourage roots to grow.
After the larva enters the stem, insecticides are ineffective, so if you choose to use a chemical treatment, you have to start early. Cook says insecticides labeled for squash vine borer include bifenthrin, permethrin, carbaryl and esfenvalerate, and spinosad, which is considered a natural insecticide. Again, be sure to follow label instructions.