Common Pests for Green Onions

Maggots

• Green onions sometimes attract onion maggots (Delia antiqua) and seed corn maggots (Delia platura). Adults of both species look like small, thin houseflies while their larvae are small, white to yellowish-white, worm-like pests that reach 1/4- to 1/3-inch long. Adult females lay eggs on the soil near host plants, and the larvae emerge and tunnel into the soil to enter onion plants and feed on the tissue. While seed corn maggots only damage young seedlings, the onion maggot also feeds on developing bulbs. Signs of maggot feeding injury include slow plant emergence and wilted, limp foliage that quickly collapses. A single maggot can kill over 20 green onions before becoming an adult fly.

Thrips

• Onion thrips (Thrips tabaci) are tiny pests that pierce plant tissue and suck out the fluids. Adult thrips overwinter near grain or legume plants and don't usually start feeding on onion plants until about mid-summer. Adult females lay their eggs on the onion leaves, with white to yellowish-white larvae emerging four to 10 days later. The feeding activity strips chlorophyll from the leaves, which results in small, white to silver blotches or streaks as well as scarred foliage. The damaged foliage areas lose moisture, which causes water stress and reduces plant growth.

Mites

• Tiny bulb mites (Rhizoglyphus robini) attack germinating seeds, onion roots and bulb tissue. Mite feeding stunts plant growth, and severe root damage causes affected plants to topple. The feeding wounds also allow fungal and bacterial pathogens to easily enter and infect green onion plants. Bulb mites typically inflict the worse damage when wet, cool weather slows plant growth. Mite populations increase quickly because each female can lay 700 eggs during her 40-day lifespan.

Pest Control

• Maggots and thrips both quickly develop pesticide resistance. Help control maggot populations by rotating crops every two years or isolating onion plants from one another. Watering plants with overhead watering methods can help reduce onion thrips populations, as can placing a straw mulch around your plants. Avoid using a broad-spectrum pesticide, since the chemicals also wipe out the onion thrips' natural predators, which include predatory mites, lacewings and minute pirate bugs. Because onion maggots, bulb mites and seed corn maggots all thrive in soils that contain a lot of non-decomposed organic matter, avoid planting any onions in weedy locations, old fields or an area freshly treated with manure.