2016 University of Minnesota Cooperative Black Cutworm Trapping Network Report #5

Week of April 16-April 22, 2016

This newsletter is available in a print-friendly pdf format: 2016 Black Cutworm Network Issue 5

bcw 2016-05 mapLast week's weather systems brought additional black cutworms into the state. Fourteen trap locations reported moth captures from April 16-22, most occurring April 19-21. Some moths were captured across the trapping network area.

A Murray County trap had a significant capture of eight moths on the morning of April 19.

A Sibley County trap captured ten moths from April 20-21. 

A Blue Earth County trap had 24 moths over the week. Unfortunately, we do not know the individual daily results (It's a busy time of year), but it is probable that eight moths / two consecutive nights occurred somewhere during the week.

Nearby, five moths were captured in Brown County, April 21-22, and Redwood County, April 21. This is less than a trigger for predicting the potential economic damage, but shows moths moving northward into most of southern Minnesota. Migrating moths are not uniformly distributed. Because of its location or the reproductive status of the migrants, pheromone traps are not equally effective at capturing unmated males. It is best to view these migration events as related to local weather systems.

I looked at the date(s) of this week's captures of eight or more and precipitation as a potential indicator for where moths may have rained out of low-level jet streams http://water.weather.gov/precip/. When looking at daily precipitation maps, remember black cutworm moths are nocturnal and the weather event that brought the moths in could have occurred the previous calendar day. The screen shots below show two of the possible systems.

bcw2016_05 weather map 1

bcw2016_05 weather map 2

Date of significant trap capture Trap location Projected cutting date
28-Mar Swift Co. 21-May
12-Apr Rock Co. 23-May
19-Apr Murray Co. 27-May
21-Apr Sibley Co. 29-May
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 April 27, 2016. Source: https://mygeohub.org/groups/u2u/gdd.
field attractive to black cutworm laying moths

A low area in a field of soybean residue without spring tillage - an attractive site for egg-laying black cutworm moths. The early season weed populations, common lambsquarters in this case, increase the attractiveness. The moths can find these weedy areas well before the plants are large enough to see them from the road. Incorporating dense weed stands like this can create a seed corn maggot problem if tillage and planting are done when flies are active.

What factors increase risk for black cutworm damage?

1) Moths arriving into the area in large numbers to lay eggs is an obvious driver.

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 attractive egg-laying moths

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

5) Moths arriving earlier with  respect to spring tillage and planting increase risk. Late planted corn is at more risk because it is exposed to larger larvae when small.

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.

For more information on assessing risk from black cutworm damage see: What makes a corn field high risk for black cutworm?

The planting date of corn, the size and timing of black cutworm flights detected with pheromone traps and degree-days can be used together to predict risk of cutworm damage. This does not mean that you can ignore scouting as other species of cutworm or other stand reducing insects may be about: Black and Other Cutworm Species in Minnesota Corn

- Bruce and Travis