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)
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.
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.
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
Iowa 141 79
Illinois 43 34
Missouri 8 7
Minnesota 6 6
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
- “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
- “(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
- 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?
142 -- Integrated Crop and Pest Management
Page last updated:
July 9, 2006
Page maintained by Linda Schultz, firstname.lastname@example.org