2018 U of MN Cooperative Black Cutworm Trapping Network Report #6

Week of May 19-25, 2018

This newsletter is available in a print-friendly pdf format: 2018 Black Cutworm Network Report #6

Black cutworm moth captures throughout southern MN counties from May 19-25, 2018Figure 1. Maximum 2-night black cutworm moth captures by county. May 19-25, 2018.

Once again, the past week’s weather brought more black cutworm (BCW) moths to many trap locations. Significant captures occurred in Jackson and Olmsted counties.

The reported maximum 2-night moth capture for the most active trap location for each county during the week are shown in Figure 1. This will be the last black cutworm trap captured map for the season. If you have sweet corn or a large numbers of still unplanted acres in your area, feel free to run your trap longer; we will take data (the trap at Lamberton will run for the rest of this week).
Table 2 shows counties that reported significant trap captures (eight or more moths over two nights; indicating potential risk for economic damage to row crops) and dates. It also presents the degree-day calculations that predict egg hatch and beginning of leaf feeding, the start of the 4th instar (stage) larvae that are large enough to cut small corn plants, and when cutting stops and pupation begins. There were some slight adjustments to this table as degree-days after the flights have accumulated.

Things continue to favor chances of black cutworm injury this spring!

I have now received reports of leaf feeding (mostly on sugarbeets and lambquarters from Renville, McLeod and Martin Counties and cutting of corn leaves from Dakota county). Pay attention when scouting. Remember, corn hybrids without the Herculex I or Viptera trait is susceptible to black cutworm. For more information see Handy Bt trait table 2018

4th instar larvae and 5th instar larvae, which are large enough to cut seedling corn stems, should now be from most of the earlier fights! The next week or so is a critical scouting window. 5th and early 6th instar larvae do the most feeding and as a result damage.

How do you know how far along a cutworm larva and how much damage it can do? Table 1 has some guidelines.

Black cutworm size and damage potential tableTable 1. Black cutworm size and damage potential.

As cutworm begin to cut corn, a generic threshold is 2-3% cut plants and larvae less than ¾ inch long, 5% if larvae are more than ¾ long. Corn cut above the growing point will recover. By burying into the growing point, large larvae sometimes kill up to 5-6 collar corn. These will be present into the 3rd week of June. More precise economic threshold calculations for black cutworm can be found in the Extension fact sheet: https://www.extension.umn.edu/agriculture/corn/pest-management/black-cutworm/. This fact sheet provides information on what makes a field attractive to black cutworms, cutworm growth and development and tips on cutworm scouting and management. Pay close attention to the sections on scouting, cutworm development and economic thresholds as your corn scouting begins.

Previous black cutworm reports can be found at https://swroc.cfans.umn.edu/agricultural-programs/pest-management/black-cutworm-reporting-network.

Thanks to all of the cooperators who are maintaining traps and Minnesota Corn Research and Promotion Council for support. Because delays in spring tillage or late-planted crops prolong the length of time that fields are attractive to egg-laying moths, we will still take data if cooperators are willing.

If you find black cutworm damage in your corn, soybean, sugarbeet and other crop scouting this spring, we would like to hear about it. When they are compared to trap results, field reports of cutworm size and population density can help improve our predictions.

Until next week,

Bruce Potter (bpotter@umn.edu cell: 507-276-1184) and Travis Vollmer

Table 2. Significant moth flight capture locations, dates and larval development predictions. These projections are guidelines only. Italicized dates are based on 30-year average temperatures. The rate of development is influenced by microclimate temperatures that are influenced by factors such as slope and aspect, residue and soil moisture.
County 2-night capture Biofix date Post-flight Degree-days as of May 29th Estimated BCW stage Estimated start leaf feeding1 Estimated start of cutting2 Projected end of cutting3
Blue Earth 8 3-May 381 5th instar 12-May 27-May 16-Jun
Dakota 8 8-May 329 4th instar 18-May 29-May 19-Jun
Faribault 10 8-May 314 4th instar 17-May 29-May 19-Jun
Jackson 11 8-May 301 3rd instar 18-May 30-May 20-Jun
Jackson 8 19-May 192 2nd instar 26-May 8-Jun 26-Jun
Martin 20 2-May 382 5th instar 11-May 27-May 16-Jun
Martin 12 9-May 299 3rd instar 18-May 31-May 20-Jun
McLeod 10 4-May 391 5th instar 12-May 26-May 15-Jun
Murray 9 2-May 392 5th instar 10-May 27-May 15-Jun
Nobles 27 1-May 397 5th instar 12-May 26-May 15-Jun
Olmsted 8 2-May 355 4th instar 10-May 28-May 18-Jun
Olmsted 13 21-May 158 2nd instar 27-May 10-Jun 28-Jun
Pipestone 9 4-May 384 5th instar 14-May 27-May 17-Jun
Redwood 8 3-May 389 5th instar 10-May 27-May 15-Jun
Rock 11 3-May 390 5th instar 18-May 27-May 15-Jun
Rock 8 9-May 309 3rd instar 19-May 31-May 20-Jun
Rock 14 10-May 297 3rd instar 19-May 31-May 20-Jun
Rock 21 11-May 291 3rd instar 19-May 1-Jun 20-Jun
Steele 11 9-May 289 3rd instar 19-May 1-Jun 21-Jun
Swift 9 7-May 330 4th instar 17-May 29-May 19-Jun

1Based on 90 degree-days (base 50oF) after significant flight (leaf feeding begins).

2Based on 312 degree-days (base50oF) 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 50oF) after significant flight pupation.