Tuesday, May 22, 2012

Corn rootworm egg hatch is happening now

Like all insects, corn rootworm matures based on heat. Eggs overwinter and hatch into larvae based on accumulating soil degree days. We can expect about 50% of the population to hatch when 684-767 degree days are reached. Southwestern Iowa is experiencing 50% corn rootworm egg hatch right now. The rest of the state will hit that target in 7-14 depending on future temperatures.

Predicted corn rootworm egg hatch in Iowa for 2012. Click here for current degree day accumulation for corn rootworm. Map courtesy of Iowa Environmental Mesonet, ISU Department of Agronomy.

I strongly encourage you to scout for rootworm damage later this summer, especially in continuous corn fields where populations can be higher. I expect larval establishment to be high this year, so estimating root damage is important for gauging population densities. For more information on the 2012 corn rootworm egg hatch in Iowa, read this ICM News article posted today.

Thursday, May 17, 2012

Bean leaf beetles are hungry

In March, I predicted low overwintering mortality based on our mild winter. You may have noticed adults become active in alfalfa starting in April. Some soybean research plots around southern and central Iowa have decent numbers feeding on unifoliates. Read more about early-season management of bean leaf beetle here.

 Soybean can compensate for early-season defoliation by bean leaf beetle. Photo by Erin Hodgson (17 May 2012 near Ames, IA).

Circular-shaped defoliation on leaves is an indicator of bean leaf beetle feeding, even if you don't see the beetles. Photo by Erin Hodgson (17 May 2012 near Ames, IA).

Friday, May 11, 2012


In May, reports from around the state have indicated leafhoppers are rising in numbers. The species we are most familiar with in Iowa is potato leafhopper. They are small, bright green and have white eyes. Note the spiny legs and clear wings that extend well past the end of the abdomen. Treatment thresholds for alfalfa can be found here. Consider reducing this threshold for high-quality dairy hay.

Potato leafhopper adults are about 1/8 inches (3 mm) long. Photo by Marlin E. Rice.

A few places in Iowa, Nebraska and the Dakotas have reported another species, aster leafhopper, in fields this year. They are a little bigger and have an olive green or brown body. Aster leafhoppers have a wide host range and are can be a pest of vegetables, field crops, and ornamentals. A treatment threshold for alfalfa and other field crops isn't well defined. That is partly because they can vector a plant disease called aster yellows. Cost-effective treatment decisions would be dependant on disease severity in combination with leafhopper density. Aster yellows has similar visual symptoms to barley yellow dwarf virus in small grains. So consider an insecticide application when symptoms first appear (e.g., yellow or mottled leaves) or if clouds of leafhoppers are disturbed when walking through fields. Pyrethroids are generally effective but may need to be reapplied if migratory populations reinfest fields.

Aster leafhopper are about 5/32 inches (4 mm) long and have a wedge-like body. Photo by Whitney Cranshaw, www.ipmimages.org.

Tuesday, May 8, 2012

Stalk borers on the move

Iowa has been steadily accumulating degree days ahead of schedule in 2012. Over the weekend, some parts of southern Iowa hit an important degree day benchmark for common stalk borer. About 10 percent of stalk borer larvae can begin moving to corn after accumulating 1,300 to 1,400 degree days. Part of southwestern and southeastern Iowa have reached that threshold and we recommend starting to scout this week in corn. Central and northern Iowa should start scouting May 12 to May 18, if warm temperatures continue. This is about three weeks earlier than last year. 

 Growing degree days accumulated (base 41°F) for stalk borer larval movement in Iowa for 2012. Begin scouting around 1,300 to 1,400 degree days. Map courtesy of Iowa Environmental Mesonet, ISU Agronomy. 

For the full ICM News article about stalk borer management, click here.