Onion Thrips (Thrips tabaci) are tiny insects that hide between tightly folded onion leaves and feed by scraping plant cells and sucking out their contents. Feeding produces characteristic silvery-white streaks or patches that can eventually turn brown. Heavy infestations reduce the leaf area available to produce the bulb, resulting in smaller onions. Thrips reproduce rapidly during hot, dry weather, so populations can increase surprisingly quickly.

How to Fix It
Check leaf folds: Look deep between the leaves for tiny yellowish or brown insects when silvery damage first appears.
Water stressed plants: Thrips damage is generally worse on drought-stressed onions, so maintain consistent soil moisture.
Remove crop debris: Clean up onion foliage and weeds that can harbour thrips.
Encourage beneficial insects: Predatory insects, including minute pirate bugs and lacewings, feed on thrips.
Insecticidal soap: Thorough contact with the insects is necessary, so direct spray into the protected spaces between leaves.
Spinosad: Spinosad can control heavier infestations. Use carefully around flowering plants and pollinators.