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Inspect Corn for Western Bean Cutworms ASAP

       
       
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(Visit the Western Bean Cutworm Image Gallery for more photos)

The western bean cutworm used to be found mainly in western Nebraska
feeding on corn and edible beans.

In fact, I first saw this insect in North Platte, NE in 1988 when I was still
a struggling Ph.D. student at UNL.  Well, it now appears that the western
bean cutworm has followed me here in SD.

Western bean cutworms caused significant damage on corn ears in
eastern SD last season and are again threatening to cause damage
this year.

SDSU Agronomy Educator Ron Thaden (Clay County), and Crop
Consultant Larry Sax (Minnehaha County) have already reported
infestation levels ranging from zero  to 40% infested corn plants as
of Friday (July 27, 2001).

Tasseling corn must be inspected for western bean cutworm eggs
or newly hatched larvae as soon as possible.  Corn raised for seed is
especially vulnerable.

Egg masses can be found on the upper surface of corn leaves.  There
may be between 5 to 200 pinhead-sized eggs per egg mass.  Newly laid
eggs are white in color but turn purplish within a week then hatch.

Under a hand lens or microscope, each egg has ridges and the top
looks like a dome.  Care must be taken when identifying western bean
cutworm eggs as they can be mistaken for stink bug eggs which are
barrel-shaped and do not have ridges.

Newly hatched larvae are dark brown in color and can be found feeding
on the tassel, green silk in the ear, and leaves.  These larvae will eventually
settle inside the ears as soon as the silks dry up and the kernels start to form.

Western bean cutworms can be effectively controlled before they reach the
corn ears.  However, once they settle inside the ears and start feeding on the
developing kernels, insecticide treatments will be ineffective.

Consider treatment with an insecticide if 8% of the corn plants have egg
masses or newly hatched larvae.  Western bean cutworm larvae directly
destroy corn kernels in the ears hence the very low economic threshold.
For corn raised for seed, treatment is suggested if 5% of the plants are
infested.

Insecticides labeled for use against western bean cutworm larvae on corn
include:  Asana XL (2.9-5.8 fluid ounces per acre), Capture (2.1-6.4 fluid
ounces per acre), Lorsban 4E(1-2 pints per acre), Pounce 3.2EC (2-4 fluid
ounces per acre), and Sevin XLR Plus (2 quarts per acre).  Always read
and follow label directions.

For more information visit the Nebraska western bean cutworm site at:
www.ianr.unl.edu/pubs/insects/g1359.htm.  The senior author, Dr. Ron
Seymour, and I were classmates at UNL.

Web posted on July 31, 2001 by Mike Catangui  |  Revised on August 7, 2001 by Mike Catangui

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