Efficacy of Insecticides to Control Soybean Aphids in Illinois, 2000
John T. Shaw, Kevin L. Steffey, and Michael E. Gray

Summary

Plot Information and Methods

Location

James Kalkner farm in Carroll Co. Illinois

Plot Size

Two rows ´ 20 ft for each treatment in each replication, with one untreated row between each treatment. Between each replication was a 10-ft alley. Soybean row spacing was 30 in.

Experimental Design

Randomized complete block with four replications, with two untreated controls in each replication. Data collected from the untreated control plots were averaged for the ANOVA.

Soybean Variety

Golden Harvest '2595' Roundup Ready.

Pre and Post-treatment Infestation

All plots were sampled on August 26, just before treatment and again three and 10 days after treatment (DAT) . Each sample consisted of 10 center leaflets of the trifoliolate leaf. Aphids were sampled by taking the center leaflets from 10 trifoliate leaves collected from the top portion of the canopy. Leaflets were placed in plastic bags and treated with ethylene glycol to kill the aphids, thereby preventing production of nymphs. Aphids per leaflet were counted during examinations under a microscope and the mean numbers of aphids per leaflet were determined. Densities of soybean aphids per plot before insecticides were applied are shown in Table 8.1.

Environmental Conditions at Time of Application on August 26, 2000

Wind-light with 2-4 mph gusts
Canopy-dry
Air temperature-76°F

Method of Insecticide Application

Insecticide treatments were broadcast with a CO2 back-pack sprayer with four 8002VS nozzles calibrated to deliver 16.0 gpa at 20 psi. Sprays were applied over the center two rows of the four-row plots.

Statistical Analysis

Data were analyzed with the Agriculture Research Manager (ARM) version 6.1.6, from Gylling Data Management, Inc.(GDM). Means were separated by Duncan's New Multiple Range Test (MRT) (P=0.05).

Results and Discussion

Before the application of insecticides, all plots were sampled to determine the densities of aphids in each of the designated plot areas. Densities of aphids among plot areas before treatments were applied were not significantly different (Table 8.1). The average number of aphids in the untreated control plots was 53.9 aphids per leaflet. Three days after the treatments were applied, aphid densities in the untreated control plots had increased to an average of 144.9 aphids per leaflet. However, aphid densities "crashed" (effects of natural enemies dispersal) to an average of 8.6 aphids per leaflet in the untreated control plots 10 DTA.

Densities of aphids in all insecticide-treated plots were significantly lower than densities of aphids in the untreated control plots 3 DAT (Table 8.1). No significant differences in densities of aphids occurred among the insecticide-treated plots 3 DAT. By 10 DAT, because aphid densities had "crashed," there were no significant differences in densities of aphids among all plot areas.

Table 8.2 shows the percentage reductions in numbers of aphids from pretreatment levels to levels on both 3 and 10 DAT, based upon average numbers in the plots before treatments were applied and average numbers in the same plots 3 and 10 DAT. Eight treatments (Penncap-M, Lorsban 4E, Leverage, Dimethoate, EXP 61824A, Actara, Fulfill + nonionic surfactant, and Lannate SP) reduced numbers of aphids by 95% or more by 3 DAT. Warrior T applied at 0.025 lb (AI)/acre reduced the number of aphids by 93.4% by 3 DAT. Safer Soap had no effect on the density of aphids by 3 DAT.

By 10 DAT, numbers of aphids had been reduced by at least 90% in 11 plots treated with insecticides (Table 8.2): Penncap-M, Lorsban 4E, Warrior T at 0.025 lb (AI)/acre, Warrior T at 0.015 lb (AI)/acre, Provado at 0.025 lb (AI)/acre, Leverage, Dimethoate, EXP 61824A, Actara, Fulfill + ionic surfactant, and Lannate SP. Five treatments reduced numbers of aphids by at least 80% by 10 DAT: Provado at 0.047 lb (AI)/acre, Baythroid 2E at 0.025 and 0.044 lb (AI)/acre, Warrior T at 0.02 lb (AI)/acre, and Asana XL. All but one insecticide, Pounce 3.2EC, reduced numbers of aphids by at least 75% by 10 DAT.

Several registered insecticides and some experimental products show promise for controlling soybean aphids if their densities reach economic levels in 2001. However, because aphid densities "crashed" in the untreated control plots in 2000, determination of the residual efficacy of the insecticides tested in the trial was tenuous.

Table 8.1: Soybean aphid (Aphis glycine) insecticide efficacy trial, Carroll County, Illinois, 2000

Treatment

Rate¹

Mean no. aphids per leaflet²

Pre-spray

3DAT

10 DAT

Penncap - M

0.625

47.55

a

0.50

b

0.45

b

Lorsban 4E

0.5

28.80

a

0.35

b

0.25

b

Warrior T

0.025

50.00

a

2.60

b

0.10

b

Warrior T

0.015

35.77

a

7.43

b

0.50

b

Provado

0.025

56.10

a

11.55

b

2.85

b

Provado

0.047

24.90

a

12.43

b

2.57

ab

Baythroid 2E

0.025

51.67

a

27.94

b

7.57

ab

Baythroid 2E

0.044

48.37

a

10.60

b

7.23

ab

Leverage

0.0633

59.60

a

1.10

b

1.00

b

Dimethoate

0.25

58.00

a

0.90

b

0.20

b

EXP 61824A

0.05

51.20

a

0.60

b

0.03

b

Actara

0.023

43.45

a

1.40

b

0.85

b

Fulfill
+ nonionic surfactant

0.086
0.25v/v

40.07

a

0.27

b

0.10

b

Safer Soap

2.0

36.85

a

38.75

b

8.95

ab

Warrior T

0.02

51.35

a

22.70

b

5.30

ab

Pounce 3.2 EC

0.1

36.60

a

11.95

b

17.10

a

Asana XL

0.03

40.93

a

26.83

b

6.20

ab

Lannate SP

0.45

34.80

a

1.50

b

0.93

b

Control

40.94

a

197.14

a

14.73

ab

¹ All rates are specified as lb (AI)/acre.
² Means in a column followed by the same letter are not significantly different (P = 0.05; Duncan's New MRT).

Table 8.2 Percent reduction of soybean aphid (Aphis glycine) per leaflet for insecticide efficacy trial, Carroll County, Illinois, 2000

Treatment

Rate¹

% Reduction in aphid populations

0-3 DAT

0-10 DAT

Penncap - M

0.625

98.92

98.55

Lorsban 4E

0.5

98.75

99.10

Warrior T

0.025

93.39

99.71

Warrior T

0.015

69.95

97.96

Provado

0.025

81.26

94.77

Provado

0.047

57.07

90.21

Baythroid 2E

0.025

47.76

79.54

Baythroid 2E

0.044

78.78

85.39

Leverage

0.0633

98.15

98.32

Dimethoate

0.25

98.36

99.62

EXP 61824A

0.05

98.59

99.94

Actara

0.023

96.95

97.53

Fulfill
+ nonionic surfactant

0.086
0.25v/v

99.17

99.64

Safer Soap

2.0

---

75.98

Warrior T

0.02

53.12

89.03

Pounce 3.2 EC

0.1

67.18

46.29

Asana XL

0.03

28.96

84.96

Lannate SP

0.45

97.35

96.49

Control

-494.83

57.99

¹ Rates are specified as lb (AI)/acre.

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