2017 U of MN Cooperative Black Cutworm Trapping Network Issue 9

Southern MN counties with reports of at least one 2017 economic infestation of black cutworm larvae in corn.

Figure 1. Counties with reports of at least one 2017 economic infestation of black cutworm larvae in corn.

Report #9 June 7, 2017

This report is also available in a print-friendly pdf format: 2017 Black Cutworm Network Issue 9

Now starting to hear scattered reports of black cutworm damage to corn. The infestations are not necessarily where they were expected, were right on time and in high risk fields. I have not been in these fields but the pictures I have seen are definitely black cutworm.

This year's results show why we need so many traps for migratory insects and why you can't count on the results of a single trap to determine risk. I'd keep a close eye on late planted corn, and sweet corn plantings. In soybean, do not confuse rabbit, deer and waterfowl feeding, or the hypocotyl breakage from crusting with cutworm damage.

We have started to receive scattered reports of black cutworms in field corn in several SC/SE counties all along the southern border of Minnesota: Freeborn Co., Tony Sommer and Brian Weller; Faribault Co. Andy Linder; Mower Co., Lynn Lagerstedt, and Blue Earth Co., Brian Weller (Figure 1).

In all cases, larvae were about ¾ inches long or less (about half-grown). The start of 4th instar and ability to cut corn in the Faribault County can be fairly accurately determined to be on or near Saturday, June 3. Back calculating degree-days for this location, approximately 350 degree days were accumulated between April 29 and June 3. While we did not have significant pheromone trap captures reported from this area, the April 29th date corresponds to a flight into Redwood County in SW MN (Figure 2).

Depending on temperature, the larvae from this flight will feed until late June. Fourth instar and larger larvae and can cut smaller corn below the growing point. Larger larvae can kill up to V5-V6 stage corn if the larvae tunnel into the growing point.

The fields we are receiving the reports on were into soybean residue, no-till in one case and later planted corn and V3 or less in size. Where reported, they did not have a Bt trait effective against cutworms.

2017 seasonal total moth counts

Figure 2. Counties where significant moth captures occurred during 2017 are shaded in red. Numbers relate to total moths captured at that site.

If you are interested in prioritizing corn scouting efforts for black cutworm, this is the hierarchy I would use to start - expanding your scouting if you find problems.

  1. Fields in soybean during 2016.
  2. Fields with no spring tillage before April 29, 2017.
  3. Fields that were weedy, had green cover crops or other high residue fields.
  4. Fields planted to corn without a Herculex or Viptera trait - Do not count on the Herculex trait to protect corn from large black cutworms.

For more information on black cutworm scouting, economic thresholds see: https://swroc.cfans.umn.edu/sites/swroc.cfans.umn.edu/files/black_cutworm_facts.pdf.

For previous issues see the link at the beginning of this article. 

Please let us know of any cutworm infestations you encounter this spring!

- Bruce Potter and Travis Vollmer