Onions are the most susceptible plants to get attacked by onion fly but leeks, shallots and garlic are also vulnerable.
Early summer affected plants may collapse with leaves turning yellow as their roots are eaten by white maggots of the Onion Fly. Larvae of a second generation of maggots in late summer feed on roots and bore into the developing onion bulbs, allowing secondary rots to affect the bulb. This will reduce the storage potential of the onion crop.
Infested plants should be carefully lifted and destroyed before the maggots go into the soil to pupate. Clear away all thinnings. Cultivate land thoroughly during winter. Regularly hoe around plants.
There is currently no chemical control available for the control of onion fly on onions.