2016 University of Minnesota Cooperative Black Cutworm Trapping Network Report #8

This newsletter is also available in a print-friendly pdf format: 2016 Black Cutworm Network Issue 8

CUTTING ALERT!

bcw 2016-8 map

Total captures for the 2016 season for each trap. Red locations had a significant capture at least once during the season. Not all traps operated for the same length of time.

We have the just received our first report of black cutworm damage to corn. Rick Gilbertson had a field of corn treated in Benton County.  Larvae 1/2 inch long and were starting to cut corn on 5/18. This field was alfalfa in 2015 and has some plants that had escaped tillage last fall.

We did not have a trap in Benton County in 2016, but the timing and location of this flight correspond with the late March flight in Swift County to the SW and rain. I would be diligent while scouting corn the next week. While we did not catch large numbers of moths outside Swift county, this system on the night of March 27-28 could have dropped moths along a line from the SW corner of MN through the Twin cities with Swift, Stearns and Benton Counties lying on the northern edge of the system.  Not all traps were operating at this early date.

Leaf feeding from all early flights should now be visible on weeds or emerged corn. (Table 1)

Date* of significant trap capture Trap location Degree-days/estimated development stage Projected date to corn cutting
28-Mar Swift Co. 316 DD/4th instar cutting 19-May
12-Apr Rock Co. 282 DD/leaf feeding 23-May
19-Apr Murray Co. 189 DD/leaf feeding 31-May
20-Apr Sibley Co. 186 DD/leaf feeding 30-May
24-Apr Rock Co. 180 DD/start leaf feeding 31-May
24-Apr Meeker Co. 152 DD/leaf feeding 2-Jun
* first date if two night significant flight
Degree-day accumulations to 5/19/16

Table 1. Dates and locations of significant 2016 captures of black cutworm moths in 2015. The estimate of projected cutting date is based on accumulating 300 Degree Days (base 50ºF) after a significant capture. It uses 30-year historical temperature data for projecting future degree-days. Projections run with temperature data current to May 19, 2016. Source: https://mygeohub.org/groups/u2u/gdd

4th stage larvae are large enough to cut small corn, sometimes at or below the growing point. This occurs at approximately 311 degree-days base 50°F after the biofix (significant moth flight) observations of black cutworm larvae this spring let us know. After 640 degree-days, the larvae pupate. After the 5-6 leaf stage, corn is too large to cut, but large larvae sometimes tunnel into the growing point of up to 6 leaf corn.

Based on the trap captures, I suspect damaging black cutworm populations will be very spotty. While significant moth captures have been spotty this spring, moth captures are way above those in 2015.

The excitement has just begun. Please let us know of any economic infestations you become aware of.

What factors increase risk for black cutworm damage?

A reminder on where to focus scouting efforts for people like Bruce who can' t remember which pile on the desk he put things.

1) Moths arriving into the area in large numbers to lay eggs is an obvious driver. This is one reason why we run the pheromone traps.

2) Soybean residue seems to be attractive to egg-laying moths, and some reduced tillage systems, ridge till for example, are especially attractive.

3) Winter annual and early spring weeds attract egg-laying moths

4) Low lying portions of fields often have heavier infestations, possibly influenced by nighttime airflows.

5) Moths arriving earlier with respect to spring tillage and planting increase risk. Late planted corn, with respect to moth arrival, is also at more risk because it is exposed to larger larvae when small. Knowing when fights arrive is the second reason we run the pheromone traps.

6) Corn hybrids without the Herculex (Cry 1F) or Viptera (Vip3a) above ground Bt traits are more susceptible to feeding damage by cutworm larvae. However, very large populations of large cutworm larvae might still damage small corn with these traits.

7) Seed applied and at-plant corn rootworm insecticides provide varying levels of cutworm feeding protection.

- Bruce and Travis

Many thanks to our 2016 cooperators!

Larry Arentson Kevin Ballman Lisa Behnken Mark Bents
Mark Bernard Bob Braun Jack Brodshaug Steve Commerford
Aaron Erickson Jason Ertl Carmen Fernholz Jodie Getting
Cody Groen Dan Haubrich Tim Kerfeld Dan Koehler
Bill Miller Tim Moline Dave Nicolai Melinda Robertson
Bruce Peterson Gary Prescher Matt Prigge Curt Reese
Dave Schwartz Gale Symens Matt Salentiny Rod Sommerfield
Steve Sodeman Brian Weller Nathan Winter U of M SWROC (Travis)
Jon Zuk