Western Bean Cutworm: Field and Sweet Corn

Eileen Cullen, Extension Entomologist, UW Entomology Department

Western bean cutworm – Update from Krista Hamilton, WI Pest Bulletin (WI DATCP)

Courtesy of Volume 52 Number 16, July 27^th 2007 Wisconsin Pest Bulletin http://pestbulletin.wi.gov/index.jsp

Western bean cutworm moth captures in pheromone traps generally declined this week. The peak in moth emergence should have occurred in all areas of the state, except the north central and northeast regions. As flight subsides in southern and central Wisconsin, egg laying is expected to slow and localized populations should transition into the larval stages.

Larval infestations are expected to be very light in most fields. The exception may be near Princeton in Green Lake County where a Pioneer Hi-Bred representative reported captures of 129 moths between July 20 and 25, and 122 moths between July 13 and 19, for a total of 251 western bean cutworm moths. Nightly captures at this location ranged as high as 50 and 83 moths on July 12 and 20, the highest numbers documented since the start of monitoring this pest in 2004.

The high black light counts registered at Mazomanie since early July were an accurate predictor of subsequent larval damage in a sweet corn field within several hundred feet of the trap. The grower at the Mazomanie farm discovered large, full-grown larvae in numerous ears last week, and noted significant feeding injury to the ear tips. No larvae were detected this week, which suggests some have reached the 5th instar and ceased feeding. In the central regions, western bean cutworm larvae should have grown large enough by this point to be noticeable in infested corn tassels and ears.

Western Bean Cutworm has been detected consistently, at low and sporadic but increasing levels each year since 2004 in WI. This corn pest is native to North America and it expanding its range eastward in the Corn Belt.  The WI Pest Bulletin report above summarizes current larval activity in the state. In addition to WI DATCP summary above, I received one report from Bryan Black, CCA, Ag-Trac Consulting in Grant County near Stitzer.  Bryan observed two fields with 10-20% WBCW infestation. Larvae are ½ to ¾ inch and actively feeding on ear tips.  Bryan noted that damage was not evident until peeling back the brown silk protruding from ear tip. Bryan was able to identify the WBCW larvae from training received earlier this year (Feb 2007) through a distance education workshop (WI, IL, IA and NE entomologists), and written about in several Wisconsin Crop Manager articles earlier this spring.

For more information, please download the attached Regional Pest Alert fact sheet on Western Bean Cutworm at http://ncipm.org/alerts/wbc.cfm

Fact Sheet.pdf