Onion Maggots

Over fifty years ago, a western New York grower discovered that early radishes  are preferred to onions by the onion maggot! To test  his observation, he sowed radishes in several experimental blocks of onions and found that the roots became maggoty whereas the onions near them were  practically free from infestation. Because of his success he now uses radishes regularly as a trap crop  for the maggots. He is convinced that even though he  were to gather and burn the radishes the practise  pays because of the larger proportions of marketable  onions produced. Probably the continued destruction of the trap crop will reduce the size of later broods  the same year and in following years. 

Onion maggots are the laws of flies nearly related to house flies. They spend the winters mostly in  buildings, though some remain in the ground. In  early spring the females lay eggs on onion seedlings  and sets. A few days later the grubs hatch and gnaw  their way into the young plants. Rot and wilting soon  follow. By the end of May or early June in southern  New York the maggots mature, pupate and emerge  from the ground as fully grown flies which soon lay  eggs for a second brood. In some parts of the country  it is believed there is a third brood. Control of the  first brood is most important because it lessens the  number of insects in the second brood and consequently reduces the damage. 

Adapted from: Gardening Short Cuts

See Also: Garden Pests