Search  
Tuesday, November 18, 2008 ..:: WCM-News ::..   Login
WCM logo
Reset page
 Western Bean Cutworm Reported - Monitor Field & Sweet Corn for Egg Masses and Small Larvae Minimize
Location: BlogsWisconsin Crop ManagerInsects and Mites    
Posted by: WCM Staff 8/7/2008 12:41 PM
Western bean cutworm (WBC) moth flight, egg hatch and larval development underway in Wisconsin.

Western Bean Cutworm Reported - Monitor Field & Sweet Corn for Egg Masses and Small Larvae

Eileen Cullen, Extension Entomologist 

 
Summary Points
  • Western bean cutworm (WBC) moth flight, egg hatch and larval development underway in Wisconsin.
  • Statewide pheromone trap network is recording WBC moth emergence, peak flight and cumulative catch for 2008.
  • In field and sweet corn, pheromone traps (a.k.a. “milk jug traps”) help time scouting activities.
  • WI DATCP Wisconsin Pest Bulletin reported first egg masses of the season in Marquette County on July 24th.
  • Egg masses and larvae needed for regional research projects on WBC. If you locate infested field(s) please contact Eileen Cullen (cullen@entomology.wisc.edu). We are interested in collecting field samples of WBC. Thank you.
 The WI DATCP Wisconsin Pest Bulletin estimated August 1 (Vol. 53, No. 15 http://pestbulletin.wi.gov/) that 75% of the season's moth population has emerged in the southwest, south central and west central counties, where accumulations of 1,526 degree days (base 50°F) were surpassed. Pheromone and black light trap counts in these areas should begin to decline noticeably during the first week of August. By contrast, about 25% of the population has emerged in the east central and northern counties and the peak of the flight period will occur during or shortly after the week of August 4th. High trap counts for the week ending August 1st were 118 moths in a black light trap near Sparta in Monroe County and 108 moths in a pheromone trap near Princeton in Green Lake County.
 
WBC is a late season corn ear pest. WBC has one generation per year, with six or seven larval stages, and overwinters as a full-grown larva, inside a soil chamber. Spring development begins when temperatures exceed 50°F. Larvae pupate in May and moths begin to emerge from soil chambers in late June. Peak emergence in the Upper Midwest is typically between the second and third weeks of July.
 
The WI DATCP does an excellent job of leading the state’s WBC trapping network. UW Extension county agents and private crop consultants contribute data to WI DATCP as well. All trap capture counts are uploaded to the Western Bean Cutworm Monitoring Network maintained for the Upper Midwest by Iowa State University www.iastate.edu/trap/westernbeancutsorm/site.
 
Western bean cutworm trapping with milk jug pheromone traps began several weeks ago. So far, moths have been caught in Adams, Brown, Columbia, Dane, Dodge, Fond du Lac, Green Lake, Iowa, Jackson, Jefferson, Manitowoc, Marquette, Monroe, Portage, Richland, Sheboygan and Waupaca counties.
 
Most WBC eggs are laid during peak moth flight during the last week of July and first week of August. In general, the number of moths per trap across these positive counties ranges from 1 to 44 moths since moth emergence. These moth flight numbers are low compared to states west of WI such as IA and NE, more heavily infested in previous years. However, Wisconsin has a hot spot or two of higher trap captures such as Green Lake County where the pheromone trap near Princeton caught 108 moths over several days. For perspective, in western states during WBC outbreaks, hundreds of moths may be captured each night during peak flights. 2008 numbers in Wisconsin are lower than such outbreak levels, but do confirm we have a resident, overwintering population of WBC.
 
Krista Hamilton, WI DATCP Pest Survey, reported her first WBC egg mass in Marquette County on July 24th. A photo from that Marquette County field is provided here by Mark Moore. Eggs are laid on the upper leaf surface, on the upper part of the plant. Eggs are round are cream colored, then turn purple approximately 24 hours prior to hatch. 
 
 

  
Western Bean Cutworm egg mass, Marquette County, July 24 2008. 
Photo Courtesty of Mark Moore (Moore Communications)
 
What does the trap catch mean for corn? 
  • Managing WBC in corn depends on using the milk jug pheromone traps to detect the intensity and timing of peak flight, because most eggs are laid during this time frame. A heavy flight (so far we haven’t seen that in Wisconsin) may require checking the traps several times per week or even daily. You can also use degree days to estimate moth emergence and time scouting activities (see UWEX Publication A3856 link below). Either way, now is the time to be watching field and sweet corn for WBC.
  • Trap catch numbers (blacklight or pheromone traps) do not tell you what is happening in a particular field. Trap numbers cannot be used in treatment decisions for fields, rather they are your cue to incorporate WBC into scouting activities.
  • Moths prefer to lay eggs in fields close to tasselling. Examine 20 consecutive corn plants in 5 locations in the field to obtain a representative sample of 100 plants. Check the upper 3 or 4 leaves of each plant for presence of WBC egg masses and small larvae. Scout field corn hybrids and processing sweet corn varieties in different stages of development separately. In field corn planted to Bt Corn hybrid with WBC resistance remember to scout the non-Bt refuge.
  • Eggs are laid on the upper leaf surface, higher up in the canopy. They will be round (not flat and shingle-like, like corn borer egg masses) in groups of a few to 200, pearly white at first, then turning purple prior to hatch.
  • Tiny larvae first feed in the whorl and on the tassel. As second and third instars they move down to the silks, and then as larger larvae into the ear.
  • Economic threshold for foliar insecticide treatment is 8 percent of the field with egg masses and/or small larvae. For processing sweet corn, the threshold is reduced to 4 percent.
  • Insecticide applications must be timed close to egg hatch and when small larvae are exposed on the tassel and leaf surface. Once larvae have entered the ear, treatment is not effective.
  • A note about managing sweet corn—growers tend to have consecutive planting dates of sweet corn, which makes it likely that one or more of the plantings will be attractive to western bean cutworm females.
 

Fact Sheets and Extension Website available on Western Bean Cutworm
 
UW Extension Publication A3856. Western bean cutworm: A pest of field and sweet corn
 
North Central IPM Center Regional Pest Alert. Western Bean Cutworm.
 
Western Bean Cutworm Trapping and Short Course Web Seminar
(UW Madison Entomology Department, Cullen Lab Website)
 
 
Additional Reference
 
DiFonzo, C. 2008. Western bean cutworm alert. Vol. 4, July 23, 2006. The New Agriculture Network newsletter. http://www.new-ag.msu.edu/

 
Permalink |  Trackback
  

 Subscribe to get email notices  WCM Contacts  List of ALL articles 
 Print issue files for 2007 Minimize
  Crop Manager   Vegetable Update 
  

 Categories, RSS feeds Minimize
  

 WCM Text Search Minimize
  

 Browse by date Minimize
Display articles from or before the selected date.
All older articles 2006 - 1998, click HERE
  

Copyright 2007 by IPCM   Terms Of Use  Privacy Statement