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Corn Scouting Report: Western bean cutworm moving into central states

Pest is being found in new areas, specialists say.

The western bean cutworm is on the move, in areas of the western Corn Belt where it has not previously been seen. 

Bob Wright, Extension entomologist at the University of Nebraska – Lincoln, says western bean cutworm moths and egg masses were discovered July 7 in southern Nebraska, which gives a signal that farmers and consultants should begin scouting fields for the same. 

Since then, higher activity than normal has been detected by area agronomists for Pioneer. 

“Several areas of higher activity are being detected where pressure has not been historically significant,” the company said in an alert to growers. “Growers scheduling fungicide application are advised to scout for egg masses prior to application and add control measures where necessary.”

Life Cycle

Western bean cutworm moths lay eggs in clusters of five to 200 on the top surface of the upper third of a corn plant. The eggs require five to seven days to develop, during which time the egg color changes to tan and then to purple immediately before they hatch.

Scouting

Scouting for western bean cutworm should begin in field corn when the first moths are caught. Control decisions should be made shortly after the moth flight peaks. The moth flight usually peaks in early to mid-July.

When scouting for western bean cutworms in corn, check 20 plants in at least five areas of each field. Look for eggs on the top surface of the uppermost leaves or look for larvae in the tassel. Because corn prices are at or above $3.50 per bushel, if 4% of the corn plants have egg masses or larvae, consider applying an insecticide.

Western bean cutworm moths prefer to lay eggs in corn plants that are in the late whorl stage compared with those that have completely tasseled. Pay particular attention to later planted fields or those with uneven development. Western bean cutworm eggs that hatch when corn plants are in the late-whorl stage of growth have a high rate of survival. The larvae are well protected in the whorl or tassel.

New Scouting Tool in a Mobile App and Spreadsheet

The University has developed a “speed-scouting” method for western bean cutworm egg masses. The Western Bean Cutworm Speed Scout app allows users to speed scout cornfields to help them determine whether WBC populations have reached the action threshold for treatments. The app includes:

  • Paperless scouting with real time, in-field decision support
  • A visual aid in identifying WBC egg masses
  • Scouting data storage so you can review information without having Internet access
  • A reminder for when future scouting should be conducted

The app is available for iPad, iPhone, iPod Touch, and Android devices. The free app can be downloaded from the Apple App Store or Google Play by searching “western bean cutworm.”

It is also available as a downloadable Excel spreadsheet, Western Bean Cutworm Speed Scouting.

Treatment Recommendations

Bt corn hybrids with proteins active against western bean cutworms (for example, Cry 1F and VIP3A) appear to control the larvae very well, although not entirely, and should not need treating. See the Handy BT Trait Table for a list of commercially available Bt corn hybrids and the proteins they express.

If an insecticide treatment is warranted in corn, it should be made when 95% of the plants in a field have tasseled. This application timing increases the chance that the worms will be exposed to the insecticide, resulting in better control.

Chemigation has provided very good control of this insect, even at lowest labeled rates. Asana, Ambush, Baythroid, Pounce, Lorsban, Capture, Mustang, Penncap-M, Prevathon, Proaxis, Warrior, and Sevin are all labeled for control of western bean cutworm. Many generics with these active ingredients also will give good control.

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