Problems with seedcorn maggots in transplanted crops are popping up all over south Georgia this Spring. While this is a rare occasion (use of transplants avoids many soil borne insect problems), that makes it no less severe when it occurs. Maggots can kill tender young transplants, but cause minimal injury once the plants become established and harden off.
The adult files look like small house flies and are attracted to decaying organic matter. For this reason, they tend to be worse in fields where manure, weeds or a cover crop were plowed in just before planting. For future reference, it is generally recommended that this plowing occur at least three weeks before planting/transplanting. They still can occur in “clean” fields as the transplant media, which is high in organic matter, can attract flies once it is planted into the field.
Seedcorn maggots are worse under cool, moist conditions. This both slows the growth of the plant so that it is susceptible to damage for a longer period and is favorable to the maggots. One research report from Purdue indicated that damage to transplants dropped dramatically (from 60 to 80 percent down to 10 to 0 percent) as soil temperature increased above 70 degrees.
There are no effective rescue treatments for seedcorn maggot infestations. A pre-plant treatment with diazinon should avoid this problem, but is rarely done as the problem is rare. A foliar application with a broad spectrum insecticide after setting/resetting the plants should help suppress fly activity in the field and buy some time for plants to become established.