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
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.
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.
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,
|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|
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.