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Slightly larger than the house fly, the onion fly is a real scourge for some alliates. Reproducing at high speed, the larvae rot and devour the interior of the bulbs.
Find out the preventive tips to avoid the appearance of this pest. Are your plants already attacked? There are natural treatments!
How do you recognize the onion fly?
From the Anthomyiidae family, the onion fly (Delia antiqua) belongs to the order Diptera, under the order Brachycera. She looks like the house fly, except that she has a slimmer figure. It is recognized by the five dark bands, visible on its thorax. Its hairy body is gray-yellow, accompanied by large black legs. It has transparent wings. Its small eggs are about 1.5mm, they are white and streaked. The larvae of the onion fly are white and barely a centimeter in length.
Life cycle of this pest
Onion flies come out of hibernation in April-May, depending on the region. These adult insects reproduce at the rate of 200 eggs every two weeks. Their lifespan is one to two months. Females lay eggs in leaf axils, crowns or bulbs. A few days later, each egg releases a larva which will take more or less three weeks to develop within the host plant. After this time, the maggot sinks underground to pupate and turn into a fly. If it is below 15 ° C, the insect goes into diapause (hibernation), only to come out the following spring. There are 2 to 4 generations of onion flies per year in France, depending on the region and the weather.
Symptoms and damage
As the name suggests, the onion maggot touches the eponymous bulb, but not only! Leeks, chives, garlic and shallots can also be affected by this pest. It is the larvae that are harmful. As they grow, they nest in the tissues or at the base of the roots of the onion. They dig galleries and feed on the decaying tissue. These wounds are also gateways for disease. The seedlings pass through it, while the bulbs are more susceptible to diseases and other pests. From the outside, you will see the foliage turning yellow, then sagging. If you take an onion out of the ground, then you will observe the rotten bulb, probably infested with larvae.
- Plant carrots near the onion. This well-known culture association proves that onions scare away carrot maggots and vice versa.
- Dip your bulbs in rock powder before planting, this makes them more resistant to disease.
- Put on an insect veil, provided you have not been infested with this fly in the past.
- Avoid liquid manure or manure which can attract it, onion does not require a very rich soil.
- Plant late to avoid making onions available to young larvae.
- Consider rotating the crops every year so that the fly does not find a host plant the following spring.
Onion fly treatments
- As soon as you observe affected plants, tear them up and burn them.
- Use yellow strips of glue to trap flies in flight.
- The infusion of tansy is said to repel onion flies, use it as a sprinkler and spray, twice a week, during the breeding season.
- As a last resort, use a pyrethrum-based insecticide. Natural, it does not alter the environment. However, it does not differentiate between pests and garden helpers.