Corn Rootworm Hatch Begins For 2012

Corn Rootworm Hatch Begins For 2012

Iowa's 2012 predicted corn rootworm hatch is about two weeks ahead of the 2011 growing season.

Corn rootworm egg hatch in Iowa can occur from late May to the middle of June, depending on accumulating soil degree days, but the average hatching date is around June 6. Research suggests about 50% of egg hatch occurs between 684 to 767 degree days (base 52° F, soil). Although Iowa had a warmer-than-normal March this year, soil temperatures have been closer to normal in April and May. So the 2012 predicted corn rootworm egg hatch is only slightly ahead of normal (see map), but about two weeks ahead of the 2011 growing season.

 That's the update provided by Erin Hodgson, Iowa State University Extension entomologist and Adam Sisson, an ISU Integrated Pest Management specialist.

Rating corn rootworm damage is essential for assessing current management plans. Photo by Brent Pringnitz

"The southwest region in Iowa is experiencing 50% egg hatch now (on May 21) and other parts of the state will approach it within 7 to 14 days depending on the temperature," said Hodgson, earlier this week. Other states have also reported that corn rootworm egg hatch is underway. Illinois is reporting the earliest initial egg hatch in 35 years.

 Roger Elmore, ISU Extension corn agronomist, recently reported Iowa is 6% ahead of a normal corn planting year. So although predicted corn rootworm egg hatch is slightly ahead of normal, the larvae should have sufficient root tissue to feed on because most corn will be germinated by the time the eggs hatch, says Hodgson.

Saturated soils will diminish overall corn rootworm pressure, and the high adoption of Bt corn should decrease populations in most fields. "However, I anticipate a good larval establishment this year," says Hodgson. "Early egg hatch could mean we see adult corn rootworm emergence, too."

Predicted corn rootworm egg hatch in Iowa for 2012. ISU entomologists say you can expect 50% of the hatch to occur between 684 to 767 degree days. Map data courtesy of Iowa Environmental Mesonet, ISU Department of Agronomy - home of current degree day accumulation for corn rootworm.

Shortly after egg hatch, young rootworm larvae begin feeding on corn roots

Shortly after egg hatch, young larvae will begin feeding on root hairs and inside roots, Hodgson explains. As they develop, larvae will begin feeding on root tips. A severe infestation can destroy nodes 4 to 6 which interferes with water/nutrient uptake by the corn plant and makes the plant unstable.

"Every field should be scouted for corn rootworm damage regardless of the seed selection," she advises. "You need to dig and rate the corn roots even if Bt proteins are used. Continuous cornfields and areas with persistent corn rootworm populations are the highest priority for inspection."

Hodgson and Sisson recommend you assess corn rootworm root injury and adjust your management strategies if the average injury is above 0.5 on a 0 to 3 rating scale (see photo). Aaron Gassmann (ISU corn entomologist) has a webpage for additional corn rootworm management information, including an interactive node-injury scale demonstration and efficacy evaluations.

TAGS: Extension
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