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Early Start to Bugs vs Man

Posted: April 12, 2012

While most people think that vegetable pests are a major problem during the middle of the growing season (during the summer), there are insects that are ready to go as soon as a crop is planted - even in early spring!
Maggots are dirty white with a yellowish tinge. They are legless, cylindrical, and tapered. Full-grown maggots are 1/5- to 1/4-inch in length.  Photo by Whitney Cranshaw, Colorado State University, Bugwood.org

Maggots are dirty white with a yellowish tinge. They are legless, cylindrical, and tapered. Full-grown maggots are 1/5- to 1/4-inch in length. Photo by Whitney Cranshaw, Colorado State University, Bugwood.org

 

The early spring like weather has excited both home gardeners and vegetable growers. It has given everybody a chance to get an early start on all activities, including planting some early season crops. Take note though, we are not the only ones to take advantage of this nice weather and early season crops. Several flies of the Delia species are causing some problems in crops planted the past couple of weeks.

 

These are not mid-summer pests as they thrive in cool spring weather which we have had the past several weeks. There are several flies in this grouping such as the seedcorn maggot and bean seed maggot, but most have a similar life cycle. The fly overwinters in the soil as a pupae and will emerge in the spring at which time large groupings of flies can be found flying over freshly cultivated fields. These flies look very similar to the common house fly. After mating, the female lays her eggs in soil that is high in some type of organic matter (decaying cover crop or field that has received a manure application). Within several days the eggs hatch and the maggots start looking for food.

 

The problem occurs when vegetable seeds or seedlings are planted in the same soil that contains the maggots. They have the ability to seek out and burrow into the seed or tunnel into the stem of an emerging seedling and greatly reduce the plant's chance of survival. Not a picky eater, these maggots can feed on peas, beans, corn, cabbage, turnip, radish, onion, beet, spinach and sprouting potato. Damage was observed in recently planted onion fields in Clinton County where greater than 50 percent of the plants were affected.

 

This is a tough pest to control and options are somewhat limited, especially for the homeowner. Cultural controls include thorough incorporation of organic matter into the soil, preparation of seedbeds for rapid germination, shallow planting (encourage rapid plant growth and minimize the time the germinating seed is sitting in the soil), and planting when soil temperature are warm.

 

Vegetable growers have the option of also using insecticide treated seed or placing an insecticide in the soil at planting time. Seed treatments applied at planting should give effective chemical control with minimal amount of pesticide. For some crops, we have the option of transplant application of Admire. There are also several materials available for pre-plant incorporation that control can be applied. Post-applications, soil drenches after the damage is present, are not effective.