Soybean Aphids in Iowa – Past and Present

Marlin E. Rice

Extension Entomologist

Iowa State University

Acknowledgment

Extension Field Specialists-Crops Brian Lang, Decorah (northeast Iowa) Todd Vagts, Carroll (west central Iowa)

Soybean Aphids in 2000(year 1, confirmed counties)

Soybean Aphids in 2001(year 2, movement west, sprayed fields)

145,000 acres

sprayed

aphids move intowestern

Iowa

Soybean Aphids in 2002(year 3, few aphids, few sprayed fields)

researchplots

Soybean aphids: an early warning in 2003

Aphids in NE Iowa June 16 = 10/plant June 22 = 100/plant June 30 = 315/plant July 6 = 640/plant

July 14

Northwest IA, August, 2003Warrior, 15 bushelsCourtesy: Jeff Ashland, Great Lakes Co-op

Untreated

Untreated

Treated

Treated

1 mile rows with same variety planted straight through

Hancock County, IA, August 14, 20031 pt. Lorsban, 18 bushels

Soybean Aphids in 2003(year 4, outbreak, Iowa pilots spray 734K ac.)

Each day delay= 0.5 bushel

Response To Soybean Aphid Treatment by Day By Applicaton Date (August)Courtesy: Pioneer Hi-Bred Int'l.

y = -0.6218x + 16.621

R2 = 0.3754

-5

0

5

10

15

20

25

0 5 10 15 20 25 30

Day of August Insecticide Was Applied

Yiel

d R

espo

nse

(bu.

/ac.

)

~ 87 comparisons across Iowa in the 2003 season ~

Each day delay= 0.6 bushel

The Des Moines RegisterAugust, 2003

Soybean & Corn Yields 2003Iowa Ag Statistics, Annual Crop Summary

Soybean 32 bushels/acre Down 16 bushels/acre from 2002 Reduction of 32 percent Lowest yields since 1993 flood

Corn 157 bushels/acre Down 8 bushels/acre from 2002 Reduction of 4 percent Second highest average yield

Summary

Economic damage 2 out of 4 years Yield losses greatest in late July & early

August in 2003 “drought” may enhance aphid survival & yield

impacts 2001 NE Iowa 2002 SW Iowa 2003 northern 2/3 Iowa

Scouting is critical in 2004

Soybean Aphid Research in Iowa

Marlin E. Rice

Extension Entomologist

Iowa State University

Acknowledgment

Extension Field Specialist-Crops Brian Lang, Decorah

Northeast Iowa Research Farm Ken Pecinovsky, Nashua

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

Ap

pro

xim

ate

aph

ids

per

pla

nt

Soybean Aphid Populations, Decorah, Iowa, 2001 – 2003Brian Lang, Iowa State University Extension

2003-1

2001-1

2002-22002-3

2003-22003-3

2002-1

X

XX

X

X

X

X

X

X

XX

Year - Sites

2001 - 1

2002 - 1, 2, 3

2003 - 1, 2, 3

X = Peak in winged aphid activity.

Untreated check strips

Soybean Aphid Field Trial, Rodecap Farm, Decorah

Sprayed July 12

Small plottreatments

Sprayed July 27

Aerial Photo, August 30

IOWA STATE UNIVERSITYUniversity Extension

2001

Plot 1, Harvested Oct. 4 Plot 2, Harvested Sept. 28 Date of insecticide application Date of insecticide application. July 12 July 26 July 12 & 26 July 12 July 26 July 12 & 26

Insecticide ----------- bu./acre ----------------- ------------- bu./acre -----------------

Dimethoate 28 26 29 40 40 41Pounce 28 27 32 42 41 50Warrior 25 25 34 43 41 50Average 27 26 32 42 41 47Check 21 35

11 12

Soybean Aphid Insecticide Trials 2001Decorah, Iowa(Brian Lang, Iowa State University Extension)

Soybean Aphid Research Plots 2002 & 2003

DecorahNashua

Soybean Aphid & Bean Leaf Beetle Insecticide Trial #1, Nashua Research Farm, 2003(sprayed Aug 7, bean leaf beetle = 24 per 20 sweeps, highest soybean aphid = 214/leaflet Aug 25)

35 40 45 50

check

W arrior T 3.2 oz

Mustang Max 3.5 oz

Lorsban 16 oz

Furadan 8 oz

Baythroid 2.8 oz

Asana XL 6.4 oz

Bushels/acre

8.5 bu.

35 40 45 50

check

W arrior T 3.2 oz

Mustang Max 3.5 oz

Lorsban 16 oz

Furadan 8 oz

Baythroid 2.8 oz

Asana XL 6.4 oz

Bushels/acre

7.0 bu.

Soybean Aphid & Bean Leaf Beetle Insecticide Trial #2, Nashua Research Farm, 2003(sprayed Aug 8, bean leaf beetle = 44 per 20 sweeps, highest soybean aphid = 69/leaflet Aug 18)

0

500

1000

1500

2000

2500

3000

35006/

16

6/23

6/30 7/

7

7/14

7/21

7/28 8/

4

8/11

8/18

Check

P 62.5

P 125

G 62.5

G 125

C 62.5Ap

hid

s p

er p

lan

tInsecticides & Seed Treatments on Soybean AphidBrian Lang, ISU Extension, Decorah, IA 2003

R1 R3 R5

Summary

Several liquid insecticides provide good control of soybean aphids

Seed treatments offer promise of early-season suppression of soybean aphids