Answer: There are a number of potential culprits that attack squash.
Squash bugs are about 1/2" long, brown or grey, flatbacked, and shaped a bit like a shield. They suck the juices out of leaves and stems. They feed in groups. To control them, find their masses of reddish-brown eggs on the underside of leaves and squash them. Check regularly from spring through midsummer. The adults like to hide under boards, trash piles, etc. They can be "trapped" by putting boards around the garden in early spring. In morning, turn the boards over and kill the bugs. Watch for the nymph stage as well. They are wingless, pale, and feed together in groups.
The spotted cucumber beetle (1/4 inch long, yellow w/black stripes or spots) is a common and voracious pest of the squash, melon and cuke family of crops. They not only eat plants, they can transmit diseases among them. Your first line of defense is to cover the seedlings with floating row cover while they're small and young - when they're most succeptible to damage and disease. When the plants outgrow the cover, if the adults beetles are a problem, you can use a botanical spray such as pyrethrin. I've also heard of organic gardeners who had luck using oil of clove as a repellent. Dab a couple drops on cotton balls and place them throughout the plot, and the beetles stay away.
The squash vine borer affects vining crops, in particular squash and pumpkin. Adult moths lay eggs on stems near the plant base. After the eggs hatch, white caterpillars with brown heads tunnel into the stems to eat. They cause vines to wilt, even though they are well-watered, and eventually the plant will die. Look for entry holes and sawdust-like droppings at the base of the plants. Slit the stem lengthwise from the hole toward the tip of the vine and remove the caterpillar. Cover the stem with soil and it will reroot. To prevent them, in early summer, cover the plants with a floating row cover until flowers appear, which helps stop the moths from laying eggs.
For any of these pests, it's a good idea to rotate crops every planting season and clean up plant debris, where they can overwinter. If you are a diligent composter and manage your compost piles to reach a high temperature, and turn regularly to ensure that all of the material gets heated to destroy the pests, you can compost the debris. If your compost doesn't heat up and you had an infestation, throw the plant debris in the trash, rather than compost it.
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