Soybean
3.1 |
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Efficacy
of Insecticides to Control Soybeans
aphids in Illinois, 2000 |
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John T. Shaw, Kevin Steffey, and Michael
E. Gray
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Summary |
A
trial to evaluate the efficacy of insecticides
for control of the soybean aphid (Aphis
glycines) was established on the James
Kalkner farm in Carroll Co., Illinois,
in 2000. Densities of aphids were relatively
high before treatments were applied
and increased in the untreated control
plots by 3 days after treatment (DAT).
However, aphid densities "crashed"
in the untreated control plots 10 DAT.
Therefore, determination of residual
efficacy of all insecticides tested
was tenuous. Nevertheless, several registered
insecticides and some experimental products
reduced densities of aphids by more
than 90% on both 3 and 10 DAT |
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Plot Information and Methods
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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 - 76oF
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).
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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. |
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Table 8.1. |
Soybean aphid (Aphis glycine)
insecticide efficacy trial, Carroll
County, Illinois, 2000 |
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Treatment |
Rate1
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Mean no. aphids
per leaflet2 |
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Pre-spray |
3 DAT |
10 DAT |
| Penncap
- M |
0.625
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47.55ª
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0.50b
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0.45b
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| Lorsban
4E |
0.5
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28.80a
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0.35b
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0.25b
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| Warrior
T |
0.025
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50.00a
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2.60b
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0.10b
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| Warrior
T |
0.015
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35.77a
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7.43b
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0.50b
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| Provado
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0.025
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56.10a
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11.55b
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2.85ab
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| Provado
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0.047
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24.90a
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12.43b
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2.57ab
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| Baythroid
2E |
0.025
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51.67a
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27.94b
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7.57ab
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| Baythroid
2E |
0.044
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48.37a
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10.60b
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7.23ab
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| Leverage
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0.0633
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59.60a
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1.10b
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1.00b
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| Dimethoate
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0.25
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58.00a
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0.90b
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0.20b
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| EXP
61824A |
0.05
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51.20a
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0.60b
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0.03b
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| Actara
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0.023
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43.45a
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1.40b
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0.85b
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| Fulfill
+ nonionic surfactant |
0.086
0.25v/v |
40.07a
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0.27b
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0.10b
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| Safer
Soap |
2.0
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36.85a
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38.75b
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8.95ab
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| Warrior
T |
0.02
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51.35a
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22.70b
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5.30ab
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| Pounce
3.2 EC |
0.1
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36.60a
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11.95b
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17.10a
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| Asana
XL |
0.03
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40.93a
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26.83b
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6.20ab
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| Lannate
SP |
0.45
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34.80a
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1.50b
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0.93b
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Control |
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40.94ª |
197.14a |
14.73ab |
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1Rates are specified as
lb (AI)/acre.
2Means in a column followed
by the same letter are not significantly
different (P = 0.05; Duncan’s New
MRT |
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Table 8.2. |
Percent
reduction of soybean aphid (Aphis
glycine) per leaflet for insecticide
efficacy trial, Carroll County, Illinois,
2000 |
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Treatment |
Rate1
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% Reduction
in aphid populations |
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0-3 DAT |
0-10 DAT |
| Penncap
- M |
0.625
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98.92
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98.55
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| Lorsban
4E |
0.5
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98.75
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99.10
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| Warrior
T 1SC |
0.025
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93.39
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99.71
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| Warrior
T 1SC |
0.015
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69.95
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97.96
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| Provado
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0.025
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81.26
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94.77
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| Provado
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0.047
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57.07
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90.21
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| Baythroid
2E |
0.025
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47.76
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79.54
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| Baythroid
2E |
0.044
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78.78
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85.39
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| Leverage
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0.063
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98.15
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98.32
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| Dimethoate
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0.25
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98.36
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99.62
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| EXP
61824A |
0.05
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98.59
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99.94
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| Actara
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0.023
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96.95
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97.53
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| Fulfill
+ nonionic surfactant |
0.086
0.25 v/v |
99.17
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99.64
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| Safer
Soap |
2.0
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75.98
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| Warrior
T 1SC |
0.02
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53.12
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89.03
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| Pounce
3.2EC |
0.1
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67.18
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46.29
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| Asana
XL |
0.03
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28.96
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84.96
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| Lannate
SP |
0.45
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97.35
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96.49
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Control |
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-494.83 |
57.99 |
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1Rates are specified as
lb (AI)/acre. |
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