Western Corn Rootworm
Kansas Areawide Management Program Summary
The western corn rootworm (WCR) is one of the
most serious insect pests of corn in Kansas. Each year this
pest costs growers millions of dollars in yield losses and
insecticides to keep it from feeding on corn roots.
Eggs that have
overwintered in the
soil hatch in early
spring. Larvae feed
on corn roots until
late June or early July.
Adults emerge about
this time and feed on
corn pollen, silks and
foliage. They begin
laying eggs in July
and continue into
Corn rootworm damage
September.
Crop rotation is commonly used to manage corn
rootworm infestations because larvae only damage corn,
and beetles usually lay eggs in corn fields. Thus, first-year
corn fields seldom suffer corn rootworm injury. Fields that
have been planted to corn for consecutive years, however,
produce large numbers of beetles that can move and lay
eggs in first-year fields making them more vulnerable to
rootworm injury.
Traditionally, growers trying to manage rootworms
in continuous corn fields have applied soil insecticides
at planting. These insecticides protect the roots in the
treated zone but do little to reduce rootworm populations.
Planting-time treatments usually are needed every year.
Another way to manage corn rootworms is to spray
adults, killing the beetles before they lay eggs. This can
control rootworms, but success depends on an effective
beetle scouting program and, until recently, it also required
using large amounts of conventional broad-spectrum
chemical insecticides.
Studies by the USDA in South Dakota looked at ways
to control rootworms while reducing overall insecticide
use. This publication is a summary of the data gathered
while evaluating this approach in Kansas.
The K-State USDA project involved a change in
rootworm management strategy – managing beetles over
a large geographic area rather than in individual fields. The
goal was to reduce the chances that a few untreated fields
would produce enough beetles to infest nearby fields at
levels that would pose a risk of economic damage.
Another component of the study was to use a
semiochemical that would stimulate beetles to feed on the
insecticide rather than relying on accidental insecticide
contact. Semiochemicals are naturally occurring
compounds that affect insect behavior. The semiochemical
used in this project was cucurbitacin, which is found in
vegetables such as cucumbers, squash, pumpkins, melons
and gourds. Rootworm beetles are genetically predisposed
to eat cucurbitacin when they encounter it. By mixing a
small amount of insecticide with cucurbitacin, the beetles
consume the insecticide, reducing the amount needed for
beetle control. The commercial product chosen for use in
this project was Slam®, which is a mixture of cucurbitacin
and the insecticide carbaryl (Sevin).
The Kansas areawide management project was
initiated in 1996 with a grant from the USDA. K-State
Research and Extension entomologists coordinated the
project. They selected a site and developed a protocol for
Objectives
1. Determine if an areawide management
approach can reduce insecticide use.
2. Develop and evaluate systems to
monitor adult western corn rootworm
emergence and density.
3. Evaluate a semiochemical-based bait
insecticide for the areawide management of adult western corn rootworms.
4. Evaluate the impact of semiochemical
insecticide applications on other pests
and beneficial arthropod populations.
5. Examine economic changes resulting from the areawide management of
western corn rootworms.
Kansas State University Agricultural Experiment Station and Cooperative Extension Service
evaluating areawide semiochemical control of rootworm
beetles. The site chosen was a 16-square-mile area of
irrigated production near Scandia in Republic County.
Over five growing seasons (1997-2001), beetle populations
in corn fields were closely monitored, and fields were
sprayed at treatment thresholds to control rootworm
beetles. A 4-square-mile area in the adjacent township was
used as a comparison area where beetle numbers were
monitored, but growers employed traditional rootworm
management practices such as crop rotation and/or use of
planting-time insecticides.
Participating growers allowed researchers to enter
fields, sample rootworm beetle populations and treat
fields when adult WCR numbers exceeded treatment
thresholds. Researchers recorded the number of managed
and comparison acres requiring treatment. Results showed
a significant difference in the percentage of acres that
exceeded the treatment threshold in the managed and
comparison zones (Figure 1).
When adult spraying began in 1997, approximately
the same percentage of acreage in the managed zone (68.6
percent) and comparison zone (72.8 percent) exceeded the
treatment threshold. From 1998 to 2001, the percentage
of acreage exceeding the threshold in the managed zone
ranged from 51.0 percent in 1999 to only 14.7 percent in
2001. The average over the entire period was 33.5 percent.
In the comparison zone, acreage exceeding the
treatment threshold ranged from 74.5 percent in 2001 to
87.5 percent in 2000, and averaged 82.8 percent for the
entire study period.
The most interesting differences occurred in firstyear corn where none of the acres in the managed zone
exceeded the treatment threshold in 1999, 2000 or 2001.
First-year corn in the comparison zone, on the other hand,
showed 41.4 percent, 76.2 percent and 44.7 percent of the
acreage exceeding treatment thresholds in 1999, 2000 and
Percent of acres exceeding threshold
Figure 1. Percentage of acres exceeding treatment thresholds
100
90
80
70
Key
60
Comparison
Managed
50
40
30
20
10
0
1997
1998
1999
2000
2001
Year
2001, respectively. Spraying fields with beetle populations
that exceeded a certain level reduced beetle migration
and kept first-year corn fields from reaching treatment
thresholds.
Another goal was to test the efficacy of semiochemicals for controlling rootworm beetles. Efficacy was
determined by monitoring beetles in treated fields and
evaluating rootworm larval damage the following year.
Root ratings in the management zone remained in an
acceptable range, comparable to those in the comparison
zone that had been treated with soil insecticides (Table 1,
page 3).
Researchers also evaluated various adult rootworm
monitoring techniques. The standard procedure for
monitoring rootworm beetles has been to count beetles
on selected corn plants. This is labor-intensive and can be
affected by weather, time of day and the experience of the
individual doing the counting.
This projecct tested several types of beetle traps in
order to devise a more accurate method of assessing beetle
numbers. Traps offer several advantages over traditional
techniques. They monitor beetle activity over several days,
average daily variations, and reduce the effect of sampling
differences among scouts. Two beetle traps manufactured
by Trécé® Inc. seemed to provide the best alternative to
whole-plant beetle counts.
The Trécé® Pherocon® AM trap (yellow sticky trap,
page 3) was used to monitor beetle numbers throughout
the project. Twelve traps placed systematically throughout
each field demonstrated relatively consistent results when
checked weekly. Adult treatments were initiated as soon
as fields reached treatment thresholds – an average of 25
or more beetles per week per trap or 15 beetles per trap for
two consecutive weeks.
Scouting beetles
2
Trécé® Pherocon® CRW lure traps (plastic trap,
below) were used to detect emergence of adult western
corn rootworm
beetles in order
to initiate the
field monitoring
program. These
traps consistently
caught the
first beetles.
Additional data
are needed on
Yellow sticky trap
the lure traps to
determine the
most effective trap placement within a field and how many
traps per field are needed to adequately monitor beetle
densities to establish a treatment threshold.
Throughout
the project,
entomologists
evaluated the
effect of using a
semiochemical
insecticide
on nontarget
arthropod
populations.
Lure trap
Results showed
western corn rootworm areawide management using
this semiochemical insecticide had no significant effect
on populations of nontarget arthropods in Kansas corn
fields. Using a selective adult western corn rootworm
semiochemical insecticide seems to be an environmentally
sound choice. It provides effective control when properly
timed, without disrupting beneficial arthropod populations.
Insecticide resistance is also a concern with intense
adult rootworm management. Scientists monitored the
pest to determine susceptibility to insecticides used in the
project or those commonly used for adult control. Beetle
populations exhibited increased tolerance to carbaryl
in the managed zone, but this tolerance did not seem to
affect treatment efficiency. Applicators have a choice of
insecticides to mix with semiochemical products. Based
on this study, it would be wise to alternate insecticides
when using adulticides for WCR control. This should
significantly reduce the risk of selecting for insecticide
resistance.
Two new, commercially available semiochemical
products work well with several of the registered
rootworm adulticides. These products are CideTrac®,
manufactured by Trécé® Inc. and marketed as a wettable
powder, and Invite®, manufactured by Florida Foods and
sold as an emulsifiable concentrate. Both seem to work
well if properly timed, so the choice depends on cost
and preference of using a wettable powder or a liquid
emulsifiable concentrate.
Two sampling techniques were also compared: the
crop consultant, whole-plant count procedure and the
intensive sampling procedures using Pherocon® AM traps.
Results showed that the two systems provided similar
treatment recommendations, but the whole-plant sampling
technique used by many crop consultants may signal
treatment earlier than the trap counts.
Entomologists also investigated the effect of reducing
sample numbers on treatment recommendations. Scientists
found that a sample of about 20 plants (three plants at six
sites; four plants at five sites; five plants at four sites) gave
the same treatment decisions as 60 plants (five plants at
12 sites) 90 percent of the time. When beetle populations
were near the treatment threshold, however, larger plant
samples were needed to reach the same treatment decision
90 percent of the time.
Adjacent soybean and sorghum fields were monitored
to determine if significant numbers of WCR eggs had been
laid in these fields as had been reported in some areas of
the northern Corn Belt. Beetles were always present in
these fields, but the numbers were insignificant and did not
threaten first-year corn fields.
Based on this study, the areawide management
approach seems promising in reducing acreage requiring
Table 1. Root ratings* in fields from managed and comparison zones, Kansas Areawide Project 1997 – 2001
Year
1998
1999
2000
2001
Managed
> Treatment threshold
2.34
1.96
1.66
2.26
Managed
< Treatment threshold
2.13
1.71
1.72
2.11
Comparison
> Treatment threshold
3.06
3.42
2.42
2.34
Comparison
< Treatment threshold
1.96
-
* Root ratings based on Iowa State 1-6 rating where 1 equals little or no evidence of rootworm feeding and 6 equals three entire nodes
removed by rootworm larval feeding.
3
treatment for corn rootworm – at least in areas with a
significant crop rotation. The research also found that the
semiochemical feeding stimulant was effective in reducing
the amount of insecticide needed to kill corn rootworm
beetles, and the yellow sticky traps were a reliable way to
monitor beetle populations and time beetle treatments.
In this study, the areawide approach seemed to provide
an economic advantage over traditional control methods
used in the comparison zone, based on the large reduction
in the percentage of acreage needing treatment. However,
the economics of the areawide management program may
vary among locations depending on the costs incurred for
scouting, differences in the cost of soil insecticides vs. the
aerial application of the semiochemical plus insecticide,
and the actual percentage of fields requiring treatment.
For more information on the Kansas corn rootworm
areawide project check the Department of Entomology
Web site at www.oznet.ksu.edu/pr_ramp/.
Jeff Whitworth, Phil Sloderbeck, Gerald Wilde, Randall Higgins, Kun Yan Zhu and Larry Buschman
Brand names appearing in this publication are for product identification purposes only. No endorsement is intended,
nor is criticism implied of similar products not mentioned.
Contents of this publication may be freely reproduced for educational purposes. All other rights reserved. In each case, credit Jeff Whitworth et. al.,
Western Corn Rootworm Kansas Areawide Management Program Summary, Kansas State University, May 2004.
Kansas State University Agricultural Experiment Station and Cooperative Extension Service
MF-2642
May 2004
K-State Research and Extension is an equal opportunity provider and employer. Issued in furtherance of Cooperative Extension Work, Acts of May 8 and June 30, 1914,
as amended. Kansas State University, County Extension Councils, Extension Districts, and United States Department of Agriculture Cooperating, George E. Ham,
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