Trial: 2002-SBAfoliar
Foliar applied insecticide control of the Soybean Aphid (Aphis glycines). DRAFT
Bruce
Potter, F. Breitenbach, C. Holen, D. Noetzle, K. Ostlie, D. Ragsdale,
University of Minnesota, Department of Entomology
Background
The soybean aphid (SBA) is a new pest of
Minnesota soybeans. It was first identified during the late summer of 2000 in
SE MN. SBA subsequently spread throughout the soybean growing areas of MN
during the 2001 growing season. Little information on insecticide performance
for this pest is available, especially under non-drought stressed conditions.
This trial was designed to look at
insecticide performance of compounds in several insecticide classes
(Pyrethroid, Organophosphate, Neonicotinoid). Additionally, high and low use
rates were examined for at least one compound in each insecticide class.
Site and
application information
The
trial was placed in a production soybean field near New Ulm, MN. A stream with
wooded margins containing buckthorn, Rhamnus
sp., bordered the field. This field had one of the earliest detectable SBA
populations in the area and populations had been steadily increasing. Initial
aphid populations at insecticide application averaged 33 aphids per upper
trifoliate or a rating of 7.25. These individual leaf populations translated to
over 300 aphids/plant. Soybean growth,
however, was exceptional and showed no evidence of injury by SBA. These populations should be considered
moderate based on soybean stage at infestation and soybean growth.
Cooperators: Randall Reinhart, Steve
Commerford
County: Nicollet, MN
Nearest
town: New Ulm, MN
Soil
type: Nicollet clay loam
Cultivar: Stine 1700-4.
Row
spacing: 30”
Planting
date: May 6, 2002
Design:
Randomized complete block with 4 replications
Plot
size: 10’X30’
Application
date: July 26,2002
Crop
stage at application: R3
Crop
height at application: 43 inches
Soybean
aphid population at application: 33 aphids/uppermost expanded leaf (SBA rating
7.25)
Insecticide
treatments were applied with a CO2 pressurized backpack sprayer, 8002XR flat
fan nozzles on 18-inch spacing, 20 gallons/acre, 35 PSI.
Results and
discussion
High
winds and heavy rain occurred the evening of July 28,2002 or 2 days after
treatment (DAT). This caused temporary soybean lodging and reduced aphid
populations in untreated plots by 80% at the 4 DAT rating. After this setback, SBA populations
increased in untreated checks until 14 DAT.
SBA populations were declining in untreated checks by 21 DAT. Individual treatment results are presented
in Table 1 and Figure 1.
Soybean
aphid populations were estimated by single leaf (trifoliate) samples from 20
plants/plot. The leaves selected for sampling were based on which part of the
canopy had the highest aphid populations. SBA densities were initially greatest
on the upper canopy. By 7DAT the greatest densities were located on mid canopy
leaves. This coincided with end of new leaf production. Percent SBA control data is based on raw
counts of aphids/leaf compared to untreated checks. Data were transformed to a
1-10 scale (Table 1) to perform an analysis of variance (ANOVA) and means were
separated by Duncan’s new multiple range test.
Excellent
aphid control was obtained with moderate water volume and pressure in spite of
a tall, dense soybean canopy. All treatments had significantly less aphids than
the untreated check for 4, 7and 15 DAT. Plots treated with Dimethoate 4E (56%
control) and the neonicitinoids, Actara (74% control) and Assail 70WG (.025 #/A
rate)(80% control), had greater aphid populations than other insecticides at 4
DAT. Based on 7 DAT ratings, aphid populations were significantly higher in
plots treated with Actara and the low rate of Assail 70WG. However, all
insecticide treatments averaged less than 1 aphid per leaf or greater than 99%
control at this date. Dimethoate 4E and Actara had greater aphid populations
(85% and 84% control respectively) than other insecticide treatments
(>=98%control) at 15 DAT. Although not significant, there was a trend for
lower aphid populations with the higher treatment rates for those products with
rate comparisons.
Treatment
yields are presented in Table 2. Trial yields were good for Southern Minnesota
soybean production with the trial averaging 61.2 bushels/acre. Yield
differences were not observed between
any of the treatments. Bean leaf beetle were abundant in the trial before
insecticide application. Beetle populations were well controlled by insecticide
application within and surrounding the trial. Evidence of bean leaf beetle
feeding on pods was much less than 1% of pods. Sclerotinia infected 4.7% of the plants in the trial and symptoms
of Colletotrichum were observed on
nearly all plants. Additionally, symptoms of bean pod mottle virus, likely
transmitted before insecticide application, and other disease were observed on
seed.
The
lack of yield response to aphid control raises several hypotheses: 1) The
soybean aphid populations present were not great enough to impact yield in
vigorously growing, late flowering and pod fill soybeans. 2) The storm event
after insecticide application temporarily reduced populations enough to
minimize impact of soybean aphid. 3) Other factors influenced yield to a
greater extent than soybean aphid. Unfortunately, the data in this trial cannot
test these hypotheses.
Acknowledgments: Thanks to
Scott Anderson, Steve Commerford, Derek Erickson, Tim Lendt, and Phil Price for
aphid count and application assistance
Table 1. Foliar applied insecticide control of Soybean
Aphid
Randall Reinhart farm, Nicollet County, MN 2002
Potter, Holen, Noetzle, Ostlie, U of M
|
Treatment Number |
Product |
Product Rate lbs. A.I./A |
Product Rate Product/A |
07/30/02 |
08/02/02 SBA rating1 7 DAT |
08/10/02 SBA rating1 15 DAT |
|
1 |
Untreated |
|
|
5.0 a |
6.5 a |
8.0 a |
|
2 |
Dimethoate 4EC |
0.500 |
1.0 pt. |
3.5 b |
1.8 cd |
5.0 b |
|
3 |
Lorsban 4E |
0.500 |
1.0 pt. |
1.0 e |
1.5 d |
2.0 c |
|
4 |
Lorsban 4E |
1.000 |
2.0 pt. |
1.0 e |
1.5 d |
1.8 c |
|
5 |
Warrior |
0.015 |
1.92 fl. oz. |
1.8 de |
1.3 d |
2.0 c |
|
6 |
Warrior |
0.025 |
3.20 fl. oz. |
1.3 e |
1.0 d |
1.8 c |
|
7 |
FO0570 0.08EW2 |
0.025 |
4.0 fl. oz. |
2.0 cde |
1.3 d |
2.0 c |
|
8 |
Asana XL |
0.033 |
6.4 fl. oz. |
2.0 cde |
1.3 d |
2.0 c |
|
9 |
Asana XL |
0.046 |
9.0 fl. oz. |
2.0 cde |
1.0 d |
1.8 c |
|
10 |
Assail 70WG2 |
0.025 |
0.57 oz. |
2.8 bcd |
2.3 bc |
2.5 c |
|
11 |
Assail 70WG2 |
0.050 |
1.14 oz. |
1.8 de |
1.3 d |
2.3 c |
|
12 |
Actara 70WG2 |
0.023 |
1.50 oz. |
3.0 bc |
2.5 b |
5.5 b |
|
13 |
Pounce 3.2 EC |
0.200 |
8.0 fl. oz. |
2.0 cde |
1.8 cd |
2.5 c |
|
14 |
XDE2252 |
0.013 |
3.2 fl. oz. |
1.3 e |
1.3 d |
2.5 c |
|
15 |
Nudfos |
0.500 |
1.0 pt. |
1.8 de |
1.3 d |
2.0 c |
|
|
LSD (p=0.05) |
|
|
0.9 |
0.7 |
0.9 |
|
|
CV |
|
|
29.4 |
25.6 |
22.5 |
|
|
Prob(F) |
|
|
<0.01 |
<0.01 |
<0.01 |
Means within columns
followed by the same letter(s) are not significantly different (p <0.05),
least significant difference (LSD), Duncan’s New MRT.
1 Soybean aphid density was estimated by counting the number
of aphids /trifoliate leaf from 20 randomly selected plants in the center
two rows of each/plot. Leaves were selected from the portion of the canopy
most heavily colonized at each sampling date. Aphid density was greatest on
uppermost-expanded trifoliates at the pretreatment and 4 days after treatment
(DAT) sampling and mid canopy leaves (terminal – 6 nodes) for 7 and 14 DAT
sampling.
Aphid counts/trifoliate
leaf were transformed to the following scale for analysis of variance: 1)
no SBA, 2) >0 -1 SBA, 3) >1-2 SBA, 4)>2-4 SBA, 5)>4-8 SBA, 6)>8-16
SBA, 7)>16-32 SBA, 8)>32-64 SBA, 9)>64-128 SBA, 10) >128 SBA.
2 Not currently labeled on soybeans
Table 2. Yield response to soybean aphid control
Randall Reinhart farm, Nicollet County, MN 2002
Potter, Holen, Noetzle, Ostlie, U of M
|
Treatment Number |
Product |
Product Rate lbs. A.I./A |
Product Rate Product/A |
Bushels/acre@ 13% moisture |
|
1 |
Untreated |
|
|
58.7 a |
|
2 |
Dimethoate 4EC |
0.500 |
1.0 pt. |
61.9 a |
|
3 |
Lorsban 4E |
0.500 |
1.0 pt. |
61.1 a |
|
4 |
Lorsban 4E |
1.000 |
2.0 pt. |
59.9 a |
|
5 |
Warrior |
0.015 |
1.92 fl. oz. |
59.5 a |
|
6 |
Warrior |
0.025 |
3.20 fl. oz. |
61.4 a |
|
7 |
FO0570 0.08EW2 |
0.025 |
4.0 fl. oz. |
63.4 a |
|
8 |
Asana XL |
0.033 |
6.4 fl. oz. |
60.2 a |
|
9 |
Asana XL |
0.046 |
9.0 fl. oz. |
60.9 a |
|
10 |
Assail 70WG2 |
0.025 |
0.57 oz. |
62.3a |
|
11 |
Assail 70WG2 |
0.050 |
1.14 oz. |
62.6 a |
|
12 |
Actara 70WG2 |
0.023 |
1.50 oz. |
61.2 a |
|
13 |
Pounce 3.2 EC |
0.200 |
8.0 fl. oz. |
62.6 a |
|
14 |
XDE2252 |
0.013 |
3.2 fl. oz. |
61.9 a |
|
15 |
Nudfos |
0.500 |
1.0 pt. |
60.9 a |
|
|
LSD (p=0.05) |
|
|