Scouting corn for western bean cutworms

Western bean cutworms were first detected in Michigan in 2006. This late season pest impacts field corn, sweet corn and dry beans, robbing not only yield, but quality as well.

Western bean cutworm eggs two to three days old. Photo credit: Chris DiFonzo, MSU
Western bean cutworm eggs two to three days old. Photo credit: Chris DiFonzo, MSU

Under the direction of Christina DiFonzo, MSU Department of Entomology, MSU initiated a western bean cutworm trapping network in 2007. This network provides data on the emergence and peak flight of the western bean cutworm. Peak flight does not occur the same time each year, so tracking progress through the trapping network is a good tool to determine when to begin scouting corn fields for egg masses.

  • Scout pre-tassel/tasseling corn during moth flight – once pollen shed ends, egglaying ends as well.
  • Look for egg masses on the top three to four leaves, often the flag leaf or the leaf just below it.
  • Threshold for western bean cutworm egg masses is 5 percent of plants – check 20 plants in each of five locations in the field for a total of 100 plants.
  • Spray if over threshold.
  • Walk fields before harvest to determine level of damage and quality concerns.

Trap numbers from 2007 through 2011 indicate an increase in risk for corn to be damaged by western bean cutworms. Scouting fields at the appropriate time will give an indication of the pressure in individual fields and the need to manage. Keeping good records of the Bts in hybrids is also important as the efficacy can vary and scouting information can help evaluate the effectiveness of traits against western bean cutworms.

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