Extension News

As Black Cutworms Hatch, Economic Thresholds Drop


AMES, Iowa -- A significant flight of black cutworm adults (moths) arrived in Iowa the weekend of April 18, based on pheromone trap capture data across the state. This insect is an occasional pest of seedling corn that sometimes causes significant damage in a few fields.

 “This year trap cooperators monitored 66 traps in 47 counties. Based upon the reported data, we anticipate that first cutting of seedling corn should occur May 17-18 across southern Iowa, May 18-20 across central Iowa, and May 22-23 across northern Iowa,” said Rich Pope, Iowa State University (ISU) Extension program specialist.


An article that includes a map showing the projected first cutting dates, scouting instructions and a list of insecticides currently labeled for black cutworms is available at the ISU Extension Integrated Crop Management (ICM) News Web site at www.extension.iastate.edu/CropNews/2008/0516RicePopeTollefson.htm


Scouting is even more important this year than it has been in the recent past according to Marlin Rice and Jon Tollefson, ISU Extension entomologists. The men say there are two reasons they are now recommending farmers consider lowering the economic threshold for treating this pest

“There are some new variables in the control of black cutworms. These include genetically engineered corn, higher seed prices and increased market prices of corn. First, with genetically engineered corn, remember that YieldGard® is not effective against the black cutworm; only Herculex® hybrids give some protection against black cutworm,” said Tollefson.

“Second, with the high cost of seed and expected higher returns from corn the economic threshold could be lowered. Larvae ¾-inch long are in the fourth stage and will cut several more plants before they finish feeding. If the worms are longer than one inch, they are nearly finished feeding and treatments don’t need to be applied until 5 percent of the plants have been cut. A lower threshold would be 1 percent stand loss, which would be within normal stand variability and very hard to detect. The previous economic thresholds was if cutworms were less than ¾-inch, apply an insecticide when 2 to 3 percent of the plants are cut,” said Rice.


More details on the specifics of Tollefson’s and Rice’s new recommendations can be found on the Iowa State University Extension ICM News site at www.extension.iastate.edu/CropNews/2008/0516TollefsonRice.htm



Contacts :

Jon Tollefson, Entomology, (515) 294-8044, tolly@iastate.edu

Marlin Rice, Entomology, (515) 294-1101, merice@iastate.edu

Richard Pope, Entomology, (515) 294-5899, ropope@iastate.edu

Jean McGuire, Extension Communications and Marketing, (515) 294-7033, jmcguire@iastate.edu