2018 U of MN Cooperative Black Cutworm Trapping Network Report #5

Week of May 12-18, 2018

This newsletter is available in a print-friendly pdf format: 2018 Black Cutworm Network Report #5

2-night black cutworm moth captures in MN countiesFigure 1. Maximum 2-night black cutworm moth captures by county. May 12-18, 2018

Once again, the past week brought more black cutworm (BCW) moths to many trap locations but unlike previous weeks, captures were moderate. There were some larger flights over the weekend that will show up in next week’s report.

Field work is nearing completion in many areas. Spring tillage tends to reduce the attractiveness of fields to cutworms and the numbers of traps reporting has started to decline.

The reported maximum 2-night moth capture for the most active trap location for each 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) trap captures 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. These projections are guidelines only. The rate of development is influenced by microclimate temperatures that are influenced by factors such as slope and aspect, residue and soil moisture.

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

Based on the number and location of significant captures, scouting for black cutworm should be on everyone’s radar this spring, even areas north of the trapping network. Does this mean widespread devastation from black cutworm is a certainty? No, but the risk for losses from this insect are elevated this year.

BCW eggs from these earliest significant flights should have hatched. We should be starting to see pinhole or somewhat larger feeding on corn leaves and possibly cut cotyledons and stems on weed seedlings or small sugarbeets. Black cutworm larvae should still be fairly small (1/4- or less) 1st and 2nd instars. Overwintering species, such as the dingy cutworm could be larger. 

A consultant friend reported cutworm feeding on sugarbeets and lambquarters in Renville and McLeod Counties but the species was not identified. 

Finding small cutworms is difficult but ID is important as many species have a lesser probability of reducing corn stand than black cutworm. The reason is the black cutworm’s tendency to cut below ground and below the corn’s growing point.

4th instar larvae, which are large enough to cut small, seedling corn stems, should be present the last couple days of May. As cutworm begin to cut corn, a generic threshold is 2-3% cut plants and larvae less than ¾ inch long. Large larvae can kill up to 5-6 collar corn and will be present well into June. More precise economic threshold calculations for black cutworm can be found in the Extension fact sheet below.

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/. 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.

Another excellent resource for cutworm ID is Cutworm Pests of Crops on the Canadian Prairies.

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 1. Significant moth flight capture locations, dates and larval development predicitons.
County 2-night capture Biofix date Projected leaf feeding1 Projected start of cutting2 Projected end of cutting3
Blue Earth 8 3-May 12-May 31-May 20-Jun
Dakota 8 8-May 18-May 6-Jun 24-Jun
Faribault 10 8-May 17-May 5-Jun 23-Jun
Jackson 11 8-May 18-May 6-Jun 24-Jun
Martin 20 2-May 11-May 31-May 19-Jun
Martin 12 9-May 18-May 5-Jun 24-Jun
McLeod 10 4-May 12-May 30-May 19-May
Murray 9 2-May 10-May 30-May 20-Jun
Nobles 27 1-May 12-May 31-May 20-Jun
Olmsted 8 2-May 10-May 31-May 21-Jun
Pipestone 9 4-May 14-May 1-Jun 22-Jun
Redwood 8 3-May 10-May 30-May 19-Jun
Rock 11 3-May 18-May 30-May 19-Jun
Rock 8 9-May 19-May 5-Jun 23-Jun
Rock 14 10-May 19-May 6-Jun 24-Jun
Rock 21 11-May 19-May 6-Jun 24-Jun
Steele 11 9-May 19-May 6-Jun 25-Jun
Swift 9 7-May 17-May 3-Jun 23-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.