Common Summer Squash pests

The squash vine borer (Melittia cucurbitae) is the most destructive, as the adult clearwing moth lays eggs at the base of stems and the fat white grub tunnels inside, causing sudden wilting and sawdust-like frass at holes near the soil line. Squash bugs (Anasa tristis) are flat, gray-brown insects that cluster on stems and leaf undersides, laying tidy rows of bronze eggs, and their feeding causes yellow spots that turn brown and can wilt whole plants. Striped and spotted cucumber beetles (Acalymma vittatum and Diabrotica undecimpunctata) chew leaves and flowers and carry bacterial wilt. Aphids, whiteflies, and spider mites feed on leaf undersides, and in the South the pickleworm (Diaphania nitidalis) bores into fruit. Deer, groundhogs, and squirrels may also browse young plants and fruit.

Common diseases

Powdery mildew (Podosphaera xanthii) is the most common disease, appearing as white powdery patches on leaves and stems that spread and cause early leaf death. Downy mildew shows as angular yellow spots bounded by leaf veins, with gray or purplish growth on the underside in humid weather. Bacterial wilt (Erwinia tracheiphila), spread by cucumber beetles, causes vines to wilt and collapse even when the soil is moist, and cut stems ooze a sticky white sap that strings out when touched. Mosaic viruses such as cucumber mosaic and zucchini yellow mosaic, spread by aphids, produce mottled, distorted leaves and bumpy, discolored fruit. You may also see angular leaf spot and blossom-end or fruit rots in wet conditions.

Prevention

Rotate cucurbits so squash does not follow squash, cucumbers, or melons for two to three years, since many pests and pathogens overwinter in the soil and debris. Give plants full sun and wide spacing for good airflow, and water at the base early in the day rather than wetting the foliage to slow mildew. Choose powdery mildew resistant varieties when you can, and consider succession sowing or a slightly later planting to dodge the first squash vine borer flight. Clean up and remove old vines at season end, and destroy squash bug eggs and debris where pests hide.

Organic control

Cover young plants with floating row covers from transplanting until flowering to exclude vine borers, squash bugs, and cucumber beetles, then remove the covers at bloom so bees can pollinate. Scout leaf undersides and hand-pick squash bugs, crush their egg clusters, and set out boards overnight to trap and collect adults in the morning. For soft-bodied aphids, whiteflies, and mites, insecticidal soap or neem applied to leaf undersides works well, and beneficial insects like lady beetles and lacewings help. Bt can target vine borer and pickleworm larvae if applied early to stem bases and developing fruit, and sulfur or a labeled biofungicide helps against powdery mildew if started at the first sign. Always read and follow the product label for any product, and spray in the evening to protect pollinators.

Scouting & monitoring

Begin scouting at transplanting and check at least twice a week, looking on leaf undersides for squash bug eggs and adults and on lower stems for the orange-and-black vine borer moth in early to midsummer. Watch for the small holes and sawdust frass that signal a borer inside, and inspect for striped or spotted cucumber beetles on new growth and flowers. Check the oldest leaves for the first white spots of powdery mildew, and note any sudden midday wilting that could mean vine borer damage or bacterial wilt. Look for mottled or distorted new leaves that suggest a virus so infected plants can be removed early.

Tips

Pull row covers off once flowers open so bees can pollinate, and keep hand-picking squash bugs, since staying ahead of them by even a few days makes a big difference. Plant a few extra squash and start a second sowing, because these plants grow fast and a fresh planting can outrun the pests and diseases that catch up with the first.

General home-garden IPM guidance, focused on prevention and least-toxic control. Always read and follow the product label for any pesticide, including organic products. Page updated Aug 4, 2026.