Minnesota Corn: Time to Start Scouting for Cutworms

    Black cutworm larva. Photo: Michigan State University

    To this point in 2022, migratory flights of black cutworm moths into Minnesota have been relatively light. However, from April 29 to May 1, significant captures (eight or more moths/two nights) were detected in six counties. These captures followed weather systems and rainfall patterns through the SW part of Minnesota (Table 1).

    It is important to include cutworms in your scouting efforts as you are evaluating crop and weed emergence. Continued delayed planting in some areas continues to prolong the risk for late-arriving moths.

    Leaf feeding on emerged corn or weeds will be visible for the next week or so. By the last few days of May and early June, larvae will be large enough to cut off small corn plants (Table 1). Corn cut above the growing point will recover. The concern is the black cutworm’s tendency to cut plants below the soil surface and growing point.

    Unlike corn, the growing points of broadleaf crops such as sugarbeets and soybeans are aboveground at emergence and these crops are susceptible to both subterranean and surface feeding cutworm species.

    Fields with the following criteria are at higher risk from black cutworms. Pay close attention to any depressional areas in the field.

    • Spring tillage or planting after May 1.
    • Soybean previous crop.
    • Strip or ridge-tillage
    • Field history of heavy winter annual (e.g., shepherd’s purse, pennycress) or early emerging annuals (e.g., lambsquarters) or other early-season vegetation.
    • Fields in or near counties with significant captures.
    • Corn hybrid without a Herculex® I or Viptera® above-ground Bt trait .
    • Fields without a chlorantraniliprole or neonicotinoid seed treatment or rootworm insecticide.
    Table 1. Black cutworm feeding and cutting projections based on historical average temperatures. Midwest Regional Climate Center U2U here
    County 2 night
    Approx. post-flight
    as of May 5
    current max
    BCW stage
    Est. start
    corn leaf
    Est. start
    end of
    Lincoln 10 Apr 29 159 1st-3rd instar May 13 Jun 3 Jun 22
    Murray 7* Apr 29 155 1st-3rd instar May 13 Jun 4 Jun 22
    Nicollet 10 Apr 29 193 1st-3rd instar May 11 May 29 Jun 17
    Nobles 11 Apr 29 166 1st-3rd instar May 13 Jun 2 Jun 21
    Nobles 10 Apr 30 163 1st-3rd instar May 13 Jun 2 Jun 21
    Renville 11 May 1 163 1st-3rd instar May 13 Jun 3 Jun 22

    *Less than a significant two-night capture
    1Based on 90 degree-days (base 50F) after significant flight (leaf feeding begins).
    2Based on 312 degree-days (base 50F) from significant flight.
    4th-6th instar larvae are large enough to cut corn. Small plants, e.g. sugarbeets, can be cut earlier.
    3Based on >641 degree-days (base 50F) after significant flight pupation.

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