(Past issues can be found in the archives section)

Time to Scout Univoltine Corn Borers in the North

       
                     (Click on thumbnail for a bigger picture)

Light traps in the moth flight tracking project have indicated significant moth
numbers near Aberdeen, Gettysburg, South Shore, and Dell Rapids.

Cornfields near these areas must be scouted for signs of corn borer infestations
such as active feeding by the larvae on the leaf collars, egg masses underneath
the leaves, or newly hatched larvae on the tassels.

Consider treatment with an insecticide if 20 percent of the plants show signs
of corn borer infestations (this is assuming a $1.75 per bushel corn market value,
$8 per acre insecticide-plus-application-cost, and 120 bushels per acre predicted
yield).

The economic threshold (average number of larva per plant) can be calculated
using the formula below.  If eggmasses are present, then assume that 2 larvae will
eventually survive and develop per eggmass.  On the average, each eggmass
may have 20-25 eggs.

ET = [(control cost)(11.43)] ÷ [(market value)(expected yield)]

If treatment is necessary, it should be accomplished before the larvae tunnel into
the stalk.  Growers in areas with the univoltine moth flight have this week and the
week of July 23rd to inspect their fields and decide whether or not to treat for
corn borers.  Once the corn borer larvae tunnel into the stalks, treatment with
an insecticide may no longer be effective.

The univoltine corn borer moth flight usually peaks during the first 2 weeks
of July in South Dakota.  The moths deposit most of the eggs on corn leaves
at this time.  Corn borer larvae that hatch from the eggs burrow into the stalks
in about two weeks.

South Dakota has two distinct types of moth flight: one-peaked or univoltine
along Interstate-29 northward to the North Dakota border, and two peaked
or bivoltine in counties along and south of Interstate-90.  "Transition zones"
such as Dell Rapids, appear to have 3 peaks.  Transition zones are where
the univoltine and bivoltine moth flight patterns converge producing moths
all season long.

To the south, the second flight of the bivoltine corn borer moths is expected
to begin right now then peak in mid-August  The first flight in June resulted
in light to moderate corn borer infestation of the crop.

For more information:   

 Web posted on July 17, 2001 by Mike Catangui

| Extension Entomology Home Page | Archives | ECB Moth Flight 2001