Got maggots in your vegetable field?
Using degree-day models can help vegetable growers figure out when to watch for insect pests such as corn and cabbage maggots.
This year, many vegetable crops have abundant maggot populations in Michigan. These housefly-looking insects lay their eggs on or into the soil near vegetation (live or dead), and the hatching maggots feed on plant roots and decaying organic matter. Severe infestations can cause plant death, especially in the early plant stages.
There are two species of maggots commonly found in Michigan vegetable fields: seed corn maggots and cabbage maggots. The seed corn maggots start developing at lower temperatures (39°F), therefore they appear in fields earlier in the season than cabbage maggots. Both insects prefer cooler temperatures and young plants, so damage early in the spring can be more severe than later in the season. Both maggot species attack a range of crops, but the seed corn maggot has a much wider host range than the cabbage maggot. The seed corn maggot will feed on decaying organic matter as well as roots of beans, peas, cucumbers, melons, onions, corn, peppers, potatoes, cabbage and other vegetables, while the cabbage maggot feeds primarily on roots of cole crops and, only in rare cases, on other vegetables.
Since these species have slightly different temperature requirements, you can use the MSU Enviro-weather degree-day models to figure out which one you likely have in your field. (See the seed corn maggot degree-day model and the cabbage maggot degree-day model.) For example, currently the first generation of adult seed corn maggots are flying and laying eggs in southern Michigan, but for the cabbage maggot, the overwintering generation’s flight is over and the first generation adults have not yet emerged (predicted to start in 415 degree-days, 43°F base). Thus, if you have abundant adult fly populations in your fields now, they are most likely to be the seed corn maggots.
Maggots can be controlled with soil drenches of insecticides or adding an insecticides in with the transplant water. Please use the MSU Extension Bulletin E-312 guide, 2012 Insect, Disease and Nematode Control for Commercial Vegetables, to find out what options are available for your crop. In general, avoid leaving organic matter in the field and plow your winter cover crop in as early as possible to minimize maggot infestation.
Additional resources from the University of Minnesota’s VegEdge
Dr. Szendrei's work is funded in part by MSU's AgBioResearch.