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Moth Numbers High in Second Flight of the
European Corn Borer in Southeastern SD

   
   
                 (Click on thumbnail for a bigger picture)


Light traps that monitor the activities of European corn borer moths have
indicated very high moth numbers near Beresford, Canton, Centerville,
Hurley, and Sioux Falls.

The light trap near Beresford, for example, caught 1,543 moths on the night
of August 5, 2001.  This number is higher than the peak numbers of second
brood moths during the outbreak years of 1996 and 1997.

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

Late planted corn may be vulnerable.  Established research data indicate that
each second brood corn borer larva can potentially reduce yield by 4 percent
per plant if infestation starts at silking stage, 3 percent at blister stage, 2
percent at dough stage, and no yield loss at dent stage of corn development.

Economic thresholds will depend largely on the current stage of corn development.
The economic thresholds are 38% of the plants showing infestation at silking stage,
51% of the plants showing infestation at blister stage, and 76% of the plants
showing infestation at dough stage of corn development.

No treatment is recommended if the corn plants are already in the dent stage of
development.

If treatment is necessary, it should be accomplished before the larvae tunnel into
the stalk.  Growers in areas with the bivoltine moth flight have this weekend and the
week of August 12th to inspect their fields and decide whether or not to treat for
second brood corn borers.  Once the corn borer larvae tunnel into the stalks,
treatment with an insecticide may no longer be effective.

For more information:   

Bean Leaf Beetles Go After Soybean Pods

     

Bean leaf beetles can be a very destructive pest of soybeans because
they feed directly on the pods. Damage to soybeans may include low
yield and quality due to destruction of the developing pods and seeds,
and pod clipping that may cause pods to drop to the ground.

Pod-fill stage soybeans statewide must be inspected for bean leaf beetles.

Bean leaf beetles are about one-quarter inch in length, yellowish in color
with four dark spots on the back, and have chewing mouthparts.

The economic thresholds of bean leaf beetles on pod-fill soybeans can
be calculated using a formula that takes into account the chemical-plus-
application cost, predicted yield, and the expected market value of soybeans.

For example, a soybean field planted in 30-inch rows should have an average
of 6 bean leaf beetles per-foot-of-row for spraying to be cost-effective. This
scenario assumes a yield of 45 bushels per acre, expected soybean market
value of $5 per bushel, and a chemical-plus-application cost of $8 per acre.
If using an insect net, the economic threshold is 4 beetles per sweep.

Information is also available at:
plantsci.sdstate.edu/ent/entpubs/blb_mgmt_sd.htm

Bean leaf beetles will continue to feed on soybeans until the pods turn yellow.
Scouting must be continued accordingly. Beetles on the field right now will
overwinter in soil litter and shelterbelts and will feed again on next year’s
soybeans.

Growers considering treatment later in the season need to be aware
of pre-harvest interval (PHI) of whatever product they intend to use.
Read the label carefully because some products have a PHI of up to 60 days.

Insecticides labeled for use against bean leaf beetles on soybeans in SD include:
Asana XL (5.8-9.6 fluid ounces per acre, 21-day PHI); Dimethoate 4EC (1 pint per
acre, 21-day PHI); Lorsban 4E (1-2 pints per acre, 28-day PHI); Pounce 3.2EC
(2-4 fluid ounces per acre, 60-day PHI); Sevin XLR PLUS (1-2 pints per acre, 21-
day PHI); and Warrior (3.2-3.84 fluid ounces per acre, 45-day PHI).

Web posted on August 13, 2001 by Mike Catangui

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