From the article “Alternative Methods for Maggot Control,” by Carrie Kennington, appearing in “Onion World,” March/April 2003

d Grafius, a Michigan State University researcher, said some insecticides have been effective for controlling onion maggot, but in recent years the pest has been building up resistance.

To get around that and control the problem long-term, Grafius suggested that coupling insecticides with biological and cultural methods may be the answer.

Biological Control
Testing onion maggots’ natural biological enemies, Grafius found that ground beetles provided good control.

“The downside is they are only active on the soil surface and, as you know, a lot of onion maggot activity goes on below ground,” he said. “But these beetles really did reduce the number of maggots. This is a natural enemy that we think has some potential.”

One problem with ground beetles and other natural enemies, however, is that they are very sensitive to insecticides, especially those applied foliar. One alternative, Grafius explained, is to use Trigard-treated seed.

Further research is also being conducted to investigate the effectiveness of grassy strips by fields, used to preserve areas for predators. Other enemies include the rove beetle which can parasitize up to 20 percent of maggot pupae in some situations, and a small wasp that is common after harvest which can parasitize up to 30 percent of maggot pupae.

In his research report Grafius said that post-harvest practices can also make a big difference in maggot control. Harvesting as cleanly as possible and tilling the remaining culls below sprouting depth can reduce the food available for onion maggot.