Tracking temperature to predict insect appearance | Agriculture | – Norfolk Daily News


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My last article discussed how insects survive Nebraska winters and that how small spring insect populations can grow to high levels when environmental conditions are suitable. Their population growth depends on a variety of factors, and weather conditions are some of the most important. Since long range weather prediction is difficult, predicting outbreaks of most insect pests is likewise difficult.

Insects are for the most part ectotherms. This means they do not produce their own internal body heat, like we do, but instead use heat from the environment. Because their development is in large part dependent on temperature, for some insects we can use temperature to predict their activity and appearance. One such insect is the seed corn maggot, a common pest of Nebraska corn and soybeans.Seed corn maggots overwinter as pupae, then emerge as small adult flies in the early spring. After mating, the female flies are attracted to decaying organic matter, such as decaying animal manure or plants, where they lay eggs in the soil. The eggs hatch in a few days and the larvae (maggots) feed on germinating corn and soybean seeds. There are several generations of seed corn maggot each year in Nebraska.

Insecticidal seed treatments usually protect corn and soybean from seed corn maggot injury, but when insect densities are high and conditions are cool and moist, they can damage or even kill seed treated seedlings. This has happened the last few years in Nebraska, particularly for farmers who incorporate animal or green manure in the soil just before planting.There are several cultural tactics a farmer can use to prevent severe seed corn maggot damage. Delayed planting until warm soil temperatures promote fast seed germination allows the plant to outgrow seed corn maggot injury. Planting at least two weeks after fresh manure or other fresh organic matter are incorporated into the soil can reduce the attractiveness for female flies.

A more precise way to determine when to plant is to use degree-day models. Seed corn maggots develop when temperatures are above 39°F, so degree-day models for this insect keep track of the time and temperature after January 1 that temperatures are above 39°F. The idea is to avoid planting during peak fly emergence. Peak fly emergence for the first three seed corn maggot generations occurs when 354, 1,080 and 1,800 degree-days have accumulated.Fortunately, degree-day calculations for several insect pests are done for us at Nebraska Mesonet. Information for seed corn maggot can be found in the drop-down menu at The Nebraska Mesonet site also has degree-day information for common stalk borer and western bean cutworm, among other interesting weather-related data. Information for seed corn maggot and other insect pests can also be found in the University of Nebraska-Lincoln CropWatch Newsletter at .

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