Volume
3 Issue 8
July
11, 2006
Single-Generation European Corn Borer
Management . . .
Begin Scouting
 The
European corn borer (ECB) is still the region’s number one insect
pest of corn, though Bt corn has helped take much of the
guesswork out of management. The challenge of managing borers in
northwest Minnesota has always been due to the lengthy interval of
moths emerging from overwintering sites. That is because the
region’s corn borers have the potential for one (univoltine) or two
(bivoltine) generations, and they emerge at different times (Figure
1). Most effort in NW MN and ND are directed at managing
the single-generation borers.
Field Scouting
Corn should be monitored weekly for at least five weeks once plants
exceed an extended leaf height of 17 inches. At that height, corn
borer larvae will be able to survive on the plant. Inspect plants
for the presence of egg masses, whorl feeding, and live larvae.
Observing moth activity around field margins or within the field may
alert you to developing infestations
Using Degree Days for Scheduling Scouting
Activities
 Degree
day models have been used to predict the occurrence of bivoltine and
univoltine flights of corn borer moths. The models predict important
biological events based on daily temperatures. As with other degree
day models, the models should help identify priority times for field
scouting. The univoltine model predicts the proportion of moths that
have emerged and using moth emergence estimates of larval population
development can be made (Figure
2). The model is based on accumulated degree days from
April 1 when using a Max-Min, modified base 50 F which is the same
method used for monitoring corn growth with Growing Degree Days.
MN-ND degree day information for corn borer is at:
WI-MN Cooperative Extension Agricultural Weather
Page
http://www.soils.wisc.edu/wimnext/corn/euroborer.html
ND Ag Weather Network
http://ndawn.ndsu.nodak.edu/index.html
Treatment Decisions
Control of ECB in northwest Minnesota during most years will be
necessary only for first brood borers of either bivoltine or
univoltine types. Second brood populations, or the second generation
for the bivoltine borer, usually have minimal impacts on yield.
Field scouting for first brood borers should begin in late June and
continue through July.
 The
need to treat for ECB can be determined by using a simple
threshold method based on percent infestation or by a more
dynamic threshold method which takes into account
treatment costs, individual field yields and current market
conditions (Table
1).
Simple threshold:
In areas where bivoltine infestations in whorl stage corn occur,
treatment should be considered in field corn when 40-50 percent of
the plants in dryland corn or 25-35 percent of the plants in
irrigated corn have shot-holing in the whorl, egg masses on
undersides of leaves or live borers visible in whorls. Be sure that
live borers are still visible in the whorls. If not, then very
likely most of the borers have tunneled into the stalks, in which
case an insecticide treatment will not be effective.
Dynamic Threshold:
Whorl-stage corn . . . . Pull the whorls from 10 plants at 5
locations across the field. Select whorls at random, avoiding
purposely selecting damaged plants. Unwrap the whorl leaves, and
count and record the number of live larvae found. Use the
observations to determine percent plants infested and the number of
live larvae per infested plant. This method can work for both
bivoltine and univoltine type borers. Be aware that univoltine
borers often infest corn in the tassel stage (mid to late-July),
causing some difficulties in checking for live borers on plants.
Phillip Glogoza
Regional Extension Educator—Crops
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