Mild winter easy on insects but weather plays a bigger factor

Mild conditions this past winter were easy on insect pests as well as people, a University of Nebraska-Lincoln entomologist said.

Lack of extremely cold winter weather favors survival of overwintering insects in the state. However, lots of other factors help determine whether insects will cause crops harm this spring and summer, said Bob Wright, UNL field crops specialist.

"A mild winter isn't enough to predict whether individual fields will experience economic loss, but generally does suggest that there will be good survival of insects that reached the end of last year's growing season," he said.

Weather conditions during this growing season will be a bigger factor in insect numbers throughout the spring and summer, Wright said. Many insects thrive in warm, dry conditions.

Rainy spring weather can encourage development of parasitic fungi and other microorganisms that foster insect diseases and death, Wright said. Insects susceptible to such diseases include: Clover leaf weevil, alfalfa weevil, European corn borers and chinch bugs.

Other conditions that could affect insect numbers this spring include:

--Cool, wet weather when grasshopper nymphs emerge can reduce their survival by limiting their ability to feed.

--Saturated soil at the time rootworm eggs hatch may drown larvae in low portions of fields or areas with finer textured soils.

--Spring rainfall also may reduce survival of western bean cutworm larvae in the soil, particularly in finer textured soils.

Planting dates and weed control play a big part in whether fields will experience insect damage, he said.

Bean leaf beetles will be attracted to the earliest emerging soybeans in the area.

"Avoiding early planting of soybeans relative to others in your area will reduce the likelihood of injury from bean leaf beetles on seedling soybeans even if overwinter survival was above normal," he said.

Producers who have to plant early should scout those fields starting at crop emergence.

"You also might consider the use of an insecticidal seed treatment such as Cruiser or Gaucho, which will help protect seedling soybeans from early-season feeding by bean leaf beetles," Wright said.

In corn, high numbers of rootworms last year means they'll be back this year if that field is planted back to corn, he said.

"In these situations, crop rotations, using a Bt corn with activity against rootworms or the full-labeled rate of a granular or liquid insecticide would be good options to provide rootworm control," he said. "Remember, insecticide seed treatments are suggested for use against low to moderate populations of rootworms. These products may not provide adequate root protection against high populations of rootworms.

"Overall, not every field is going to have an insect problem this year, but if you've had problems in the past you need to take these control measures into consideration," he said.

In addition, several insects do not overwinter in Nebraska, but migrate from the south each spring. These insects include: Black cutworm, potato leafhopper, corn earworm, fall armyworm, green cloverworm and painted lady (thistle caterpillar).

Date: 4/18/06

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