Western bean cutworm flight in central Michigan is up from recent seasons

August 03, 2018

Dry bean growers should be aware of this increased flight, but don’t panic.

WBC moth — Western bean cutworm moth resting in dry bean canopy. All photos by Fred Springborn, MSU Extension.

Peak flight of western bean cutworm occurred largely over the week of July 21-28, 2018, in Michigan’s Montcalm area. There are still a significant number of moths being captured in some pheromone traps as of Aug. 2.

Several western bean cutworm pheromone traps have passed the mark of 150 total moths captured for the season, but it is important to remember the rest of the guidelines:

Greater than 150 moths captured in pheromone traps, plus…
Neighboring pre-tassel corn fields have egg masses, plus…
Blossom and pod feeding observed in dry beans.

From my own observations and from what local agribusiness scouts are reporting, egg masses are few and small in pre-tassel corn. This may be an indication that the number of eggs produced per moth may be much lower than what we experienced in the 2009 and 2010 growing seasons. Remember, it is not the moths that feed on dry beans, it is the larvae that hatch from the eggs produced by the moth. Lots of moths producing few eggs may be no more of a threat than a small number of moths producing big egg masses.

WBC Feeding
Western bean cutworm larvae feeding on a bean pod in 2010 when populations were near an all time high.

Check fields periodically for signs of western bean cutworm larval blossom and pod feeding this week and through August. In particular, growers of large seed dry beans such as kidney beans should consider an insecticide application if feeding is detected, especially if those beans are heading for a quality sensitive market. Insecticide applications should begin at least seven to 14 days after peak flight has occurred. Be sure to observe pre-harvest intervals and read and follow label directions.

Montcalm area trap counts 2018
Nearest town	July 20	July 27	Aug. 2	Total
Stanton 1	14	24	18	56
Stanton 2	18	41	5	64
Sidney	171	205	61	437
Sheridan	231	183	73	487
Greenville 1	62	67	26	155
Greenville 2	143	241	96	480
Trufant 1	55	62	39	156
Trufant 2	57	57	29	143
Coral	91	227	37	355

This article was published by Michigan State University Extension. For more information, visit https://extension.msu.edu. To have a digest of information delivered straight to your email inbox, visit https://extension.msu.edu/newsletters. To contact an expert in your area, visit https://extension.msu.edu/experts, or call 888-MSUE4MI (888-678-3464).