The Cabbage Maggot (Delia radicum) is a small fly that is a pest on most cruciferous vegatable. Larvae feed on the roots, causing plant death in cases of sever infestation.

Cabbage Maggot Life Cycle Stages

Cabbage Maggots overwinter as pupae in the soil, and adults emerge in late spring or early summer. Adults feed on pollen or nectar until they are ready to lay eggs in the fruit. After larvae emerge and feed on the roots before pupating. In most cases, there can be 1-3 generations in a year.

The period of adult emergence is key for insect prevention, both for placing traps and for using insecticides, if necessary. Researchers have created the Cabbage Maggot Emergence Growing Degree Day Model to better predict when the adults will emerge from the soil.

Calculating Growing Degree Day Units

The Cabbage Maggot Emergence Growing Degree Day model uses a lower threshold of 43F. 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.

Using Jan. 1st as a default “biofix” date, or starting point for accumulation. The first adult emergence occurs at approximately 301 GDD.

Source:

Eckenrode, C. J., and R. K. Chapman. 1972. Seasonal adult cabbage maggot populations in the field in relation to thermal-unit accumulations. Ann. Entomol. Soc. Amer. 65: 151-156.