ISU Extension to Agriculture and Natural Resources

A Four-State Western Bean Cutworm Pheromone Trap Network to Track Moth Emergence and Improve Scouting

Richard Pope, Extension Program Specialist, Entomology (and Plant Pathology)

Situation

Western bean cutworm (WBC) is an insect pest of corn that emerged as an economic pest in west-central Iowa in the last decade. Since then, WBC has been observed in cornfields in central Iowa. WBC is difficult to manage, because moth flight (egg laying) and resultant larval emergence occurs in July when cornfields are difficult to scout. Additionally, WBC larvae enter ears where their feeding can cause severe damage to developing kernels. The window of opportunity for treatment is usually 7 to 10 days, starting with egg hatch and ending when the larvae enter the ears. Some producers have reported up to 40% yield reductions, but damage can vary greatly from field to field.

Objective

Three key issues need to be addressed concerning economically successful management of WBC in the upper Midwest, namely, knowledge of the local presence of populations of WBC, the factors that affect WBC infestation in corn, and the timing of moth emergence and subsequent oviposition and larval presence. Pheromone traps are useful in monitoring emergence of WBC, and emergence patterns can be followed to focus scouting of fields.

Activities/Output

We recruited a network of volunteer agriculturalists to establish and monitor traps. These volunteers posted trap-capture data to www.ent.iastate.edu/trap/westernbeancutworm. This website was made public and promoted through the ISU Integrated Crop Management newsletter, as a Partnership Perk (an expedited e-mail notice to the Iowa State University (ISU) Corn and Soybean Initiative partners), through a news release from ISU communications, and in live radio broadcasts. We cooperated with Pioneer Hybrids personnel and our ISU Field Crop Specialists for trap locations in Iowa and Missouri. Additionally, Kevin Steffey at the University of Illinois recruited cooperators that used our protocol and posted to the ISU Website, and the University of Minnesota posted data gathered from 6 light-trap locations in southern Minnesota.

In total, there were 198 reporting traps placed in 116 counties in Iowa, Illinois, Missouri and Minnesota. The traps and counties covered by state were:

                        State                        Trap locations                        Counties
                        Iowa                        141                             79
                        Illinois                        43                             34
                        Missouri                      8                               7
                        Minnesota                  6                               6

Impact/Outcomes

WBC known presence: From this year’s trap network, we expanded the known range of WBC east to Will County Illinois on the Indiana border, and south to Montgomery County Illinois, near Terra Haute, IN. Also, large regional populations were identified in Benton, Buchanan, Delaware, Jones, and Linn counties in Iowa that were not previously known.

In late August we sent an e-mail survey to our trap cooperators asking them several questions about how they used the data, its value to them and what if any suggestions they have for future work with WBC. The following responses address both the dissemination of information to producers, and highlight some of the needs for future research on WBC.

Thirty-nine individuals responded to this survey, 46% (18 of 39) reported they scouted corn fields based on trap data.
We asked (among those who did scout) what the percentage of plants that had egg masses or larvae present. Twelve of the 18 found larvae and/or egg masses, and percentages of plants with them ranged from less than one to 100 percent; eight found larvae or eggs that exceeded our current suggested economic threshold of 8% of plants.
Six producers reported treating fields with insecticide, with Asana and Warrior being the most common insecticides used.
These 6 producers reported treating 6,000 acres in 2005 for WBC.
Reported estimates of yield loss were highest in Buchanan County, Iowa with an estimated ranged from 2 to 17 percent throughout the area.
Based on data from only cooperators reporting, projected corn yield losses because of WBC damage was estimated at 125,000 bushels. There were 5 cooperators reporting that there was feeding, but they couldn’t estimate losses.

Other comments volunteered by the survey respondents are listed here:

“My thoughts are that this is an interesting pest that doesn’t exhibit an easy treatment alternative. Herculex® suppresses it but will not be bulletproof. It appears for now we will have to use the best means of control available. I am anticipating higher counts next year, and I am seeing a (sic) much more activity in my customer’s fields from year to year. Thanks for allowing me to help in your research.”
“I did not see any moths until July in Dekalb or Ogle counties in Illinois, even though there were captures in several surrounding counties. We discovered they are indeed coming into Illinois! We will trap and scout much more heavily next year thanks to your program. Thanks for all the help.”
“(It is) a very difficult pest to scout for. The number of moths caught in our trap this year was down from what we trapped last year, yet there has been significant ear feeding in the field. With our current pheromone traps are we just trapping for males? If so, maybe we have yet to develop a consistent correlation between trapping the males and the amount of egg masses likely to be deposited.”
“WBC a lot worse in this area than previously thought. Extended flight period! Egg masses seemed smaller and more sporadic (than we previously thought). Scouted traditionally hot spots, but we were never able to find sufficient numbers when scouting. Now finding damage in many fields scouted, and un-scouted. I believe many will be in for a surprise this fall if they have not yet seen the damage.”
“I had to re-scout twice this year in several fields (Buchanan County Iowa). It looks as if the mid-maturity hybrids will be the hardest hit, with most of these fields having at least 1 worm in every ear now and many ears with 2 or 3. I think that there are a lot more acres that should have been sprayed, and there will be a lot of surprised farmers this fall. When scouting, I probably should have kept a cumulative count for each field on my second and third scouting trips and sprayed when the cumulative number reached 8%, but because I never found 8% egg masses or larvae at any one time there are several fields that should have been treated and weren’t.”
WBC is a lot worse in this area than anyone previously thought. Also, the flight period was quite extended.
This is a growing problem.
Thank you for this program, though I caught no moths I am now aware of this pest and will monitor again next year.
Damage seems to depend on pollination date.
Can we tie this data together with degree days?

2005
142 -- Integrated Crop and Pest Management

Page last updated: July 9, 2006
Page maintained by Linda Schultz, lschultz@iastate.edu