2020 UMN Cooperative Black Cutworm Trapping Network Report #5

2020 University of Minnesota Cooperative Black Cutworm Trapping Network 

Report #5 Week of April 25 – May 1, 2020

For more information: https://z.umn.edu/bcw-reporting

May 6, 2020

Greetings:

This past week, moth captures increased but numbers at each positive location were still low (Figure 1).  Remember, we use eight or more moths / two nights as an indicator of increased potential for economic crop damage from the resulting larvae.

Most migrant moths arrived the night of April 28 – 29 following a weather system from west to east (Table 1) across the state. Most captures were single moths/night with higher captures in parenthesis. There are likely some moths that have made it into counties where traps have not yet captured a moth but overall, this year’s migration has remained relatively light. 

BCW2020 MN

Date                 County with capture

April 25            Martin
April 26            Steele, Waseca
April 27            Blue Earth, Brown, Faribault, Fillmore (2), Renville (3)
April 28            Cottonwood (2), Jackson, Le Sueur
April 29            Brown, Cottonwood, Faribault, Fillmore (2), Martin, Meeker, Mower, Murray (4), Nicollet, Olmsted, Ottertail, Pope, Renville (2)
April 30            Brown (4), Fillmore, Houston, Jackson, Martin, Nobles (2), Sibley (4), Steele, Swift
May 01            Mower, Renville

Table 1  Positive captures in pheromone traps reported April 25- May 1.

 Black cutworm moths arriving in Minnesota seek out areas with crop debris, sheltered areas, and low-lying spots in the field to lay eggs. Any early season weed growth is very attractive to the moths. Areas with dense populations of winter annual (e.g. shepherds’ purse) and early spring emerging broadleaf weeds (e.g. lambsquarters) are often infested. Similarly, overwintering cover crops might attract egg-laying moths and black cutworm damage associated with winter rye has been observed in Minnesota corn.

 Unworked fields, or fields with reduced tillage and more crop debris is on the surface, attract more egg laying moths. Fall tillage that buries crop residue and spring tillage that eliminates early spring weed growth before the flight arrives reduces the risk and severity of black cutworm attack. Historically, soybean residue is more attractive than corn, but this may be in part due to the amount of fall tillage or to species and numbers of broadleaf weeds in the seedbank between the two crops.   

How do you focus your scouting efforts for black cutworm? Fields that are at highest risk are fields that had not been worked when moths arrive, fields with winter annuals or early spring emerging weeds and in the case of corn, field planted to hybrids without a  Cry1F (HX1) or Vip 3a (Viptera) above-ground Bt traits.

In the case of corn, scouting for black cutworms should start before 300 degree-days (base 50 F) accumulate after a significant moth capture (eight or more moths/2 nights) occurs.  This is about three weeks in a typical Minnesota spring but will, of course, happen sooner if warm and later if cool. Eggs hatch and leaf feeding begin at 90 degree-days so early scouting of small broadleaf seedlings, such as sugarbeets, is important.

Although we have not yet had any significant flights of black cutworm this spring, next week,  we’ll project when larvae from these early flights will be large enough to start cutting small corn.

Bruce Potter and Travis Vollmer

This project is supported, in part, by the farm families of Minnesota and their corn check-off investment.