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Corn Borers Are Back - - Inspect Corn ASAP
       

                                                                           (Click to enlarge)

Record high numbers of corn borer moths have been captured in light traps across
southern counties in the past two weeks.

The light trap at the SE Research Farm near Beresford, for example, registered a catch of
424 first brood moths on the night of June 16th.  This kind of number has never been seen
before in that location since trapping was started in 1996.  About 200 first brood moths per
night were the previous highest counts in the same light trap in 1997 and 2000.

Agronomist Gary Nelson of Eastern Farmers Coop has similarly reported a peak of 187
moths per night on a light trap near Harrisburg on June 24th.  Peak first brood moth
numbers in that area were less than 50 moths per night in 2000 and 2001.

Corn borer moth numbers have also been high in Avon, Huron, Jefferson, Parkston,
Sioux Falls, and Concord (Nebraska).

It is the first brood of the bivoltine corn borer that currently needs attention in southern
counties.  To the north, the univoltine moth flight has just begun.

South Dakota has two distinct types of moth flight: one-peaked or univoltine north of I-90
and along and east of Interstate-29, and two peaked or bivoltine in counties along and
south of I-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.

Field inspections of corn plants near Beresford on Friday (June 28, 2002) by myself
have indicated that most of the eggs deposited by the moths have already hatched into
larvae.  Up to 4 live larvae were found per plant.  The moths were still laying eggs though
and some eggs have not hatched yet.

The corn borer larvae found in the whorl were already in their second instar stage of
development.  They will start burrowing into the stalks when they reach third instar
within 2 weeks.  Once inside the stalk, any attempt to spray for corn borers will be
ineffective.

Spraying with an insecticide is recommended if 1 out of 4 (25 percent) of the corn
plants show signs of corn borer infestations such as “shot holes” on the leaves, larvae
in the whorl, and egg masses on the underside of leaves.  This economic threshold
assumes 4 live larvae per plant, $1.80 per bushel corn market value, $8.00 per acre
insecticide-plus-application cost, and 120 bushels per acre yield potential.

Insecticides labeled for use against the European corn borer larvae include Asana XL
(7.8-9.6 fluid ounces per acre), Capture 2EC (2.1-6.4 fluid ounces per acre), Furadan
4F (1.5-2.0 pints per acre), Lorsban 4E (1-2 pints per acre), Mustang (2.9-4.3 fluid
ounces per acre), Penncap-M (2-4 pints per acre), Pounce 1.5G (6.7-13.3 pounds
per acre), Sevin XLR Plus (1.5-2.0 quarts per acre), Tracer (1-3 fluid ounces per acre),
and Warrior (2.56-3.84 fluid ounces per acre).  Always read and follow label directions.


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