The Onion Maggot (Delia antiqua) is a small fly that is a pest on onions and garlic. Larvae feed on the roots, causing plant death in cases of severe infestation.

Onion Maggot Life Cycle Stages

Onion Maggots have several generations per year. The often lay eggs in freshly tilled soil, so delaying planting can help to avoid Onion Maggot infestation, by waiting until after the larvae have developed into adults.

Researchers have created the Onion Maggot Growing Degree Day Model to better predict when the adults will emerge from the soil, and this can be used to time planting after soil tillage.

Calculating Growing Degree Day Units

The Onion Maggot Growing Degree Day model uses a lower threshold of 4.4 C. It can be calculated with daily high and low temperatures, using the sine model to estimate growing degree day units, or the Pest Prophet app can be used to calculate GDD accumulation from hourly temperature data for a specific field.

The “biofix” date, or starting point for accumulation, should be set at the time of soil tillage. After 644 GDD (C) adults will have emerged and it should be considered safe to plant, avoiding Onion Maggot larvae.

Source:

Liu, H. J., F. L. McEwen and G. Ritcey. 1982. Forecasting events in the life cycle of the onion maggot, Hylema antiqua (Diptera: Anthomyiidae): Application to control schemes. Environ. Entomol. 11: 751-755.