If you haven’t already started, dry bean growers and crop consultants should be scouting for damage from western bean cutworm. While the peak flight of western bean cutworm occurred a full week later than last year and several previous seasons, there were still a significant number of moths being captured in pheromone traps as of Aug. 12 across the state.
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.
- Neighboring pre-tassel corn fields have egg masses.
- Blossom and pod feeding observed in dry beans.
From personal observations and from what local agribusiness scouts are reporting, egg masses have been few in pre-tassel corn. With pre-tassel corn abundant throughout the flight period, western bean cutworm may have had lots of corn to deposit eggs upon, which may be diluting the population.
Despite unusual weather and later emergence than the previous growing season, we have recorded our highest moth numbers since monitoring began in 2013. As of Aug. 12, 2019, six of the 10 locations in northeast Michigan have exceeded the economic threshold of 150 cumulative moths trapped for dry beans, too.
Western bean cutworm is a pest of dry beans, field corn and sweet corn that has been present in Michigan since 2006. In Michigan, the most economically significant crop damage associated with this pest occurs in dry beans.
Adult moths will begin to emerge from the soil in July to mate and then proceed to deposit eggs in both corn and dry beans. If corn has already tasseled at the time of emergence, most eggs will be laid in dry beans. Once deposited, egg masses will hatch in five to six days, and feeding on the crop will begin.
Western bean cutworm larvae feed on the silks and young ears of corn, as well as blossoms, pods and immature seed in dry beans. This feeding can lead to poor pollination of corn and undesirable ear damage, particularly in sweet corn. In dry beans, reduced yields and seed quality can be expected.
Remember, it is not the moths that feed on dry beans, it is the larvae that hatch from the eggs produced by the moth. Check dry bean fields periodically for signs of western bean cutworm larval blossom and pod feeding this week and through the rest of August.
It will take time and patience to scout for this feeding, especially to find it early. You will not see it by driving by a field or flying over it with a drone. 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.
Photos by Fred Springborn, MSU Extension
Western bean cutworm flight, egglaying and damage is also quite variable across the landscape and can be patchy within fields, which makes careful scouting critical. Factors that seem to contribute to higher western bean cutworm moth numbers include susceptible crops in rotation (corn and dry beans), dry weather and coarse soil texture.
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.
When deciding if an insecticide application is appropriate, dry bean growers must consider their market and tolerance for damage. Insecticide applications should be timed to control the bulk of larvae shortly after they hatch, usually about a week after peak flight.
As always, applicators need to follow label instructions, including pre-harvest intervals. Many insecticides effective against western bean cutworm are restricted use pesticides requiring an applicator license to purchase and apply. Insecticides can also kill non-target and beneficial insects, which may cause secondary problems, as in the case of flaring spider mite infestations by removing their natural predators.
This article was published by Michigan State University Extension. For more information, visit http://www.msue.msu.edu. To have a digest of information delivered straight to your email inbox, visit http://www.msue.msu.edu/newsletters. To contact an expert in your area, visit http://expert.msue.msu.edu, or call 888-MSUE4MI (888-678-3464).