Onion Fly
Onion Fly  The onion fly (Delia antiqua) is a serious pest of onions in the northern United States and Canada. It attacks only crops in the allaceae family although it is not capable of maintaining high populations on wild relatives of onions. Adults of this pest emerge in May from pupae overwintering in the soil near plants. Eggs from the onion fly are laid on young leaves and stems or in soil near plants. White larvae up to 1/8 in (8mm) long feed on stems, roots and bulbs for 2 to 3 weeks before pupating. There are three to four generations per year. Susceptible Plants- members of the allaceae family.
Symptoms- Young plants wilt and die, leave and stems of more established plants become soft and rotten. The larvae of the onion fly bore into onion bulbs, which then tend to rot. Attacks are most severe in early to mid summer. Symptoms of onion fly may be confused with stem nematodes or onion white rot. The second generation onion maggot feeding on developing bulbs typically results in distorted growth accompanied by rotting tissue. Feeding by third generation maggots on late season onion bulbs results may result in an unusable crop.
Prevention and Control- Grow under row cover or fine mesh netting. The covering should be placed immediately after sowing or planting. Remove infested plants as soon as onion fly is discovered. Use a crop rotation and cultivate the soil in winter to expose pupae to natural predators DE Diatomaceous Earth is odorless and nontoxic and looks like white powder. It is composed of finely milled fossilized shells of minuscule organisms called diatoms. The microscopically fine, sharp edges desiccate the insects' exoskeletons upon contact, and the pests dehydrate and die within hours. The insects also die when they eat the dust. Biological Control - There are a variety of natural enemies that collectively help reduce populations of onion fly maggot larvae and adults. Certain predatory beetles eat both onion fly eggs and larvae. Predatory flies and birds consume the onion fly. Parasitic wasps can be found early in the season attacking first generation maggots. When environmental conditions are cool and moist in the spring and fall, a parasitic fungus Entomopthora muscae can infect large numbers of the adult onion fly. Beneficial Nematodes Insecticidal Control- Monterey Garden Insect Spray, OMRI listed, contains Spinosad, derived through fermentation of a naturally-occurring soil bacterium. Spinosad controls caterpillars, thrips, codling moth, leafminers, borers, fruit flies, fire ants, and more! Spinosad works on the insect’s nervous system, causing paralysis and then death in 1-2 days.
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