Implications of the 'significant' black cutworm flight east of Crookston on May 14

Since my arrival to northwest Minnesota, I have been a part of the UMN black cutworm monitoring network managed by IPM specialist Bruce Potter from the UMN’s Southwest Research and Outreach Center in Lamberton.

As part of the network each spring I put a trap in a tree on the edge of my rural property just to the east of Crookston (Figure 1). The operative trap components include a sticky surface on which to trap black cutworm (BCW) moths and a pheromone lure to attract them (Figure 2). 

Figure 1. Pheromone trap with a lure to attract black cutworm moths.

Figure 2. A black cutworm moth caught in a pheromone trap (photo: Angie Peltier).

 

Pheromones, or the sex hormones that are produced by female BCW moths, are impregnated into small rubber lures that are placed in the trap. These BCW pheromones attract male moths that are looking for a mate.  Unsuspecting males then fly into the trap and become stuck on the sticky surface. Traps are checked each morning, and moths identified, counted and removed.

BCWs do not overwinter in Minnesota, but fly north each growing season along with major weather systems.  When a ‘significant flight’ (aka biofix) has occurred, or when eight or more moths are trapped over a 2-night period, degree days - which are based upon historical temperature trends and their effect on BCW developmental milestones – are used to project a potential cutting date. Cutting dates can help us to better pinpoint when corn damage may occur, and when scouting should therefore likely commence.

While many corn hybrids have been genetically modified to express Bt proteins that kill BCW larvae as they feed on leaf tissue, these traits are not present in all hybrids. Additionally, one only need look at Bt-resistant western corn rootworms in Minnesota and Bt-resistant European corn borer in Manitoba to understand that over time and repeated use any management strategy can result in pests evolving resistance to that strategy. 

Below, I have adapted a table from this BCW fact sheet, to include the dates this spring that each BCW developmental milestone is likely to occur in the Crookston, MN area.

Table 1. Cumulative degree days associated with BCW developmental milestones and activity and the dates on which each activity is likely to begin in the Crookston, MN area in 2024

Cumulative degree days (base 50)	BCW growth stage	BCW activity	Projected 2024 dates (based on 1991-2020 GDD ‘normals’ at the NWROC in Crookston
0 (biofix)	Significant moth capture	Egg laying	May 14
90	Egg hatch	-	May 25
91-311	1st-3rd instar	Leaf feeding	May 25
312-364	4th instar	Cutting	Jun 12
365-430	5th instar	Cutting	Jun 15
431-640	6th - 7th instar	Cutting	Jun 23
641-989	pupa	-	Jul 2

 

 

 

 

 

 

 

Initially, the smallest BCW larvae (instars 1-3) are only large enough to feed on leaves (Table 1), but as larvae continue to grow and develop, they are large enough to actually cut across the entire whorl of a corn plant. Cutting location can vary among cutworm species. If this cutting takes place above the plant’s growing point, the plant, while growth is set back, may be able to recover.  Cutting below the growing point results in stand losses. Stand losses can lead to both lost yield potential and higher weed pressure (due to poorer canopy coverage). Insecticides are labeled for use as BCW rescue treatments.

In 2024, a significant flight occurred on May 14. Provided that the temperatures in the coming days and weeks are similar to the 1991-2020 GDD ‘normals’, cutting is likely to begin around June 12. This means that scouting should begin a few days before June 12. For scouting recommendations and additional information about BCW, consult this fact sheet or this webpage devoted to BCW.