Alfalfa weevils are hatching

Iowa has steadily accumulated growing degree days (DD) all through March. One of the first insects to hatch is alfalfa weevil. In general, we can expect egg hatch around 200 DD south of I-80 and around 250 DD north of I-80. Most of the state has already hit those benchmarks.

 

Accumulated growing degree days (base 48F) in Iowa form 1 January - 2 April 2012. This map is updated daily (click here). Map courtesy of Iowa Environmental Mesonet, ISU Department of Agronomy. 

 Alfalfa weevil is an important defoliator because adult and larval feeding can reduce tonnage and forage quality. If plants are greater than six inches, use a sweep net to initially sample. Insecticidal treatments are based on crop value and plant height. Read this recent ICM News Article for management guidelines.

Alfalfa weevil adults are brown and hairy, have elongated snouts and elbowed antennae. Photo by Joseph Berger, ipmimages.org.

Black cutworm captures continue

On March 20, we confirmed the first black cutworm moth trapped in Muscatine County, Iowa. Since then, several counties have also reported captures. Adults were trapped in Lucas County (30 March), Des Moines County (30 March), Marion County (29 March), and Story County (31 March). We use these captures to start estimating growing degree days for predicted cutting dates in corn. Normally predicted cutting dates happen in mid-May, but they may be slightly earlier this year. Look for our 2012 predicted cutting dates later this month.

Black cutworm larvae typically damage corn, but can also feed on soybean. Certain fields may be at a higher risk for black cutworm damage than others; low lying and poorly drained, next to areas of natural vegetation, weedy, and other characteristics should be scouted first.
 

Cutworms are normally noctural feeders and curl up with disturbed. Look for wilted, dead or missing plants. Top photo by Steph Marlay, bottom photo by Tracy Cameron.