"Onion maggots. ONION MAGGOT CONTROL IN HOME GARDENS

Onion maggots can occasionally be a serious pest in the home garden. Adult onion maggot flies resemble house flies with long legs and are about 1/3 inch long. Larvae of flies are called maggots and are headless and legless. Onion maggots bore into plant stems, causing the plants to turn yellow and wilt. Their tunnels make it easier for diseases to enter the bulbs and cause rot.

Onion maggots have three generations per year. Adult flies begin to emerge from pupae in the spring, usually in mid-May. Peak flights of adults occur about late May or early June. Adult onion maggot flies can survive for 2 - 4 weeks and may lay several hundred eggs. Female flies lay their eggs on the soil at the base of the seedling or in leaf sheaths, beginning about 7 to 10 days after emergence. The eggs hatch into maggots 2-5 days after being laid. The maggots develop through three larval stages in 2 to 4 weeks and feed externally or tunnel into the stem and bulb. Larvae use their hooked mouthparts to feed on the tissue of the onion plants. When mature, the maggot leaves the bulb and enters the soil to pupate at a depth of 1-4 inches. First and second generation pupae remain in the soil for 2-4 weeks before adult emergence occurs. The second flight of adults occurs in early July and the third flight in late August and September. Larvae of the third generation develop into pupae and will overwinter as pupae in the soil.

Life stages of onion maggot (photo courtesy
J. Ogrodnick, Cornell Univ., NYSAES)

Management of Onion Maggots in Home Gardens

Plant new plants in a different location from last year.
Avoid over-fertilizing with manure and high organic matter soils. Maggots prefer to lay eggs in rich soil.
Deep tilling or double-digging soil in the fall will help reduce the overwintering population of pupae.
Remove weeds at least two weeks prior to planting.
Cover seedbeds with a protective cloth or cover individual plants to prevent adults from laying eggs near plants. Various synthetic materials like polyethylene or woven plastics are available as physical barriers to prevent pest infestations and protect plants. Individual cone-shaped screen covers, made from standard window screen fixed to a wooden frame, can be useful in the home garden. They are easily constructed and can be used year after year. Covers can be removed when plants grow big enough to tolerate damage. Be sure transplants are maggot-free before planting them. Once maggots are infesting a crop, there is no reliable way to control them.
Remove infested onions from the garden, so that maggots will not be able to complete their development.
Prevention is the best management strategy as there are no insecticides available for use in the home garden."

Shallots

Here is a link that might be useful: Shallots vs onions

I tried dusting with rotenone around the base of the plants when they were small , in May . In June for several weeks you could see the adult flies mating on top of the stems . I spread pine wood chips that I use for chick bedding around the base of the plants , hoping the pine resins would deter the larvae (as they do with chick fleas) and made a couple of rotenone applications also .
The end result was about 15% crop loss , despite the heaviest infestation of flies I have ever seen .

For some reason the word "rote " got posted instead of "rotenone" , a common organic pesticide dust.

why can't this blog write the word r-o-t-e-n-o-n-e ??