Common Zucchini pests

Squash vine borers are a serious pest: the adult is a clearwing moth that resembles a wasp, and its larvae tunnel inside the stem base, causing sudden wilting and sawdust-like frass (called frass) at holes near the soil line. Squash bugs are flat, gray-brown shield-shaped insects that cluster on undersides of leaves and lay bronze egg masses along leaf veins; their feeding causes yellow speckling, wilting, and blackened, dying leaves. Striped and spotted cucumber beetles chew leaves, flowers, and stems and, more importantly, spread bacterial wilt as they feed. Aphids cluster on new growth and leaf undersides, causing curled leaves and sticky honeydew, and they can transmit mosaic viruses.

Common diseases

Powdery mildew is the most common disease, appearing as white powdery patches on leaves and stems that spread until foliage yellows and dries. Downy mildew shows as angular yellow blotches on the upper leaf surface bounded by leaf veins, with grayish fuzz underneath in humid weather. Bacterial wilt, spread by cucumber beetles, causes runners to wilt suddenly and permanently even when the soil is moist; cut a wilted stem and look for sticky, stringy ooze. Viral diseases such as cucumber mosaic and squash mosaic produce mottled, distorted, yellow-green leaves and bumpy, misshapen fruit.

Prevention

Rotate cucurbits so zucchini does not follow squash, melons, or cucumbers in the same bed for at least two to three years. Space plants generously and thin for good airflow, since crowded, damp foliage invites powdery and downy mildew. Choose powdery-mildew-resistant or -tolerant varieties when available, and water at the base with drip or a soaker hose in the morning so leaves dry quickly. Clean up and remove old vines and crop debris at the end of the season, since squash bugs and disease spores overwinter in garden litter.

Organic control

Cover young plants with floating row covers from transplanting until flowering to exclude squash bugs, vine borers, and cucumber beetles, then remove the covers so bees can pollinate. Scout and hand-pick squash bugs and crush their egg masses, and knock cucumber beetles into soapy water in the cool morning when they are sluggish. For aphids and young squash bug nymphs, use insecticidal soap or neem oil sprayed on leaf undersides, following the product label for timing and use. Encourage beneficial insects such as lady beetles, lacewings, and parasitic wasps, and for powdery mildew apply a labeled sulfur, potassium bicarbonate, or horticultural oil product at the first sign, always reading and following the label.

Scouting & monitoring

Begin scouting weekly as soon as plants are established, checking leaf undersides for squash bug eggs and adults and inspecting the stem base for the small holes and frass that signal vine borers. Watch for the first striped or spotted cucumber beetles at emergence and again at flowering, since they arrive early and vector bacterial wilt. From midsummer on, examine older, lower leaves for the first white spots of powdery mildew and for angular yellow lesions of downy mildew after humid spells. Note any sudden midday wilting and check for stem ooze to catch bacterial wilt before it spreads.

Tips

Focus on prevention: row covers until bloom plus prompt hand-picking stops most pest problems before sprays are ever needed. Because zucchini overproduces, remove and destroy the first heavily infested or diseased plant rather than nursing it along, so you protect the rest of your planting.

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.