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Large influx of black cutworm moths arrive in Minnesota

by Bruce Potter, Integrated pest management specialist

Minnesota map
Figure 1. Maximum black cutworm moth captures by county April 27 - May 4, 2018.
The past week brought rain and black cutworm (BCW) moths to many trap locations, both unwelcome. This is as large and widespread early-season influx of moths as we have seen for several years.

Many counties have more than one trap operating. The reported maximum 2-night moth capture for all traps in a county during the week are shown in Figure 1.

Table 1 shows counties that reported significant (numbers indicating potential risk for economic damage to row crops) captures and dates.

Cottonwood, Faribault and Lac Qui Parle Counties had less than the 8 moths/2-night threshold but they caught 7, 6 and 6 respectively. Unfortunately, one of the Fillmore county traps could not be checked from April 30-May 4. It had 9 moths over that time.

There appear to be several migration events that we can use for a bio-fix (event to use as a starting point) for cutworm development. The first was the nights of April 29-30 but other systems look like they brought moths May 1 – 4. If you had thunderstorms pass through your area the past week, there is a chance it brought black cutworms with.

Fortunately, we can use same base temperatures to predict both corn and black cutworm development. Using the April 30th date and historical weather data (Midwest Regional Climate Center U2U corn growing degree days), cutworm larvae should be large enough to cut corn (4th instar). This takes approximately 312 degree-days base 50°F. This ranges from May 28 in the SW corner for an April 30 - May 1 flight to June 1 for a May 4th flight in Central MN. How big will your corn be?

Things are shaping up in the favor of black cutworm and not corn this spring! Small corn is more susceptible to cutting and the later corn planting this year will lead to more corn acres in a susceptible stage. Over the next few weeks we will try to fine-tune temperature-based predictions for when cutworm cutting should begin and end. In the meantime, you can find much more black cutworm information at: https://www.extension.umn.edu/agriculture/corn/pest-management/black-cutworm/. It provides information on what makes a field attractive to black cutworms, cutworm growth and development and tips on cutworm scouting and management.

Table 1. Significant moth capture locations and dates.
County 2-night capture Date(s) Comments
Blue Earth 8 May 2-3
Martin 20 May 1-2
McLeod 10 May 4
Murray 9 May 1-2 2 traps w/ captures April 30-May 2
Nobles 27 April 30-May 1
Olmstead 8 May 2
Pipestone 9 May 3-4
Redwood 8 April 30-May 1 Traps w/ captures April 30-May 3
Rock 11 May 2-3 Also on April 30, May 1 and 4

More information on the Black Cutworm Reporting Network and weekly updates can be found at https://swroc.cfans.umn.edu/agriculturalprograms/ pest-management/black-cutworm-reporting-network.
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