SEE Mail Issue 040217 (February 17, 2004)

	Extension Entomology Mail Mike Catangui, Ph.D. Associate Professor & Extension Entomologist
February 17, 2004 (Issue 040217)

. . . . Soybean Aphids May Have Caused Up to 13 Bushels Per Acre Yield Loss in Some Fields South of I-90 in 2004 . . . .

New! Stage specific economic injury levels for V5, R2, R4, and R5

Preliminary Procedure for Calculating
the Economic Injury Level of Soybean
Aphids in R2 (Full Bloom) Soybean in
South Dakota

The 3 steps for calculating the economic injury level (EIL) of
soybean aphids on R2 (full bloom) soybean in South Dakota
are as follows:

1) Calculate the gain threshold (GT).

     GT = chemical plus application cost ÷ soybean market value

2) Express the gain threshold as a percentage of the soybean
      yield potential of the field.

     GTP = (GT × 100) ÷ yield potential

3) Calculate the EIL using a logarithmic formula developed from
      data collected by SDSU graduate student Eric Beckendorf
      during the 2003 season.

      EIL = natural antilog((GTP+8.01)/9.6)

Note: The unit of the EIL is in aphids per plant.


Example 1. Johny Malarkey farms near Canton, SD. The coop in
Canton is charging $8/acre (chemical plus application) to spray the
field. Predicted market value of soybean is $7/bushel. Johny's field
had been yielding 50 bushels per acre consistently over the years.
The soybean was planted in 30-inch rows. It is now July 14 and the
soybean is nearing full bloom. What is the economic injury level of
the soybean aphid if Johny wants to spray his soybean at full bloom
(R2) stage?

GT = $8/acre ÷ $7/bushel = 1.14 bushel/acre

EIL = natural antilog((2.29+8.01)/9.6) = 2.92 aphids per plant.

= 29.2 aphids per linear foot (assuming 10 plants per foot).

= 292 aphids per ten linear feet.

Example 2. Buford Malarkey (Johny's cousin) farms near Elk Point,
SD. The Elk Point Farmer's Coop is charging $12/acre (chemical
plus application) to spray the field. Predicted market value of
soybean is $9/bushel. Buford's field had been yielding 45 bushels
per acre consistently over the years. The soybean was planted in
30-inch rows. It is now July 14 and the soybean is nearing full bloom.
What is the economic injury level of the soybean aphid if Buford
wants to spray his soybean at full bloom (R2) stage?

GT = $12/acre ÷ $9/bushel = 1.33 bushel/acre

EIL = natural antilog((2.96+8.01)/9.6) = 3.14 aphids per plant.

= 31.4 aphids per linear foot (assuming 10 plants per foot).

Note: This procedure is for use in South Dakota only. It is based
on preliminary data. Research is currently ongoing at SDSU and
USDA-ARS in Brookings, SD.

For more information visit our sites: Soybean Aphid in South Dakota

Soybean Aphid ET in South Dakota

EIL Calculator for South Dakota

Ear is the Achilles' Heel

Know Your Bt-Corn

Greek mythology has it that Achilles was dipped into the river Styx by
his mother to make him invincible (except for his heel) during battles.

I am of the opinion that corn hybrids containing both the Cry 1 Ab and
Cry 3Bb1 genes are pretty much invincible from injuries from two of the
most damaging insect pests of corn in SD - European corn borer and
corn rootworms.

However, I think that the Achilles' heel of the stacked corn hybrids
is the corn ear because it is not protected against western bean
cutworms late in the season.

Western bean cutworms can cause moldy seeds. And grain quality
is now paramount if a grower wants to sell corn to ethanol plants that
also sell by-products for use as feed to livestock.

I looked up the dictionary and found that Achilles' heel is defined as
"a seemingly small but actually crucial weakness."

At this point in time, we could also all benefit from reviewing the
meaning of that rarely used "h" word in science and technology -
hubris.

For more information: Cry 1 Ab Crying Over Western Bean?

FDA Fumonisin Guidance

FDA Aflatoxin Guidance

© Copyright 2009 by South Dakota State University. All Rights Reserved.