2004 Foliar applied insecticide control of the Soybean
Aphid (Aphis glycines).
Bruce Potter - IPM Specialist, University of Minnesota Southwest Research and Outreach Center
Summary
A soybean aphid insecticide efficacy trial was placed in a commercial soybean field near St. James, Watonwan County, MN. To rates of Asana XL, Baythroid, Lorsban 4E, Baythroid + Lorsban 4E, Mustang Max, Trimax and Warrior were evaluated. Additionally, Warrior was evaluated in combination with an anti-drift agent, non-ionic surfactant. The aphid population at this site began to increase relatively late (R4) and applications were made August 11, 2004 to R4.5 soybeans at 383 aphids/plant. The untreated plots accumulated over 3700 aphid days but populations remained below 300 aphids/plant for the duration of the trial. Yield differences between treatments were not observed. Lorsban 4E applications experienced the most rapid aphid decline. Pyrethroids required 6-14 days to reduce populations below those in plots not treated with insecticide. At 14 DAT, the treatments containing Lorsban 4E and Warrior had lower aphid populations. The 2.8 oz rate of Mustang Max and both Trimax treatment rates performed similarly to untreated. Other products were intermediate in performance. The addition of adjuvants did not affect performance of Warrior and the 2 oz rate of that product performed similarly to the 3.2 oz rate.
These data suggest that low rates of insecticide
may not provide adequate control of soybean aphid and that soybean can tolerate
a moderate aphid infestation without yield loss.
The soybean aphid (SBA) is a relatively 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 with localized yield limiting populations in 2002. During the 2003 growing season, this insect required treatment over most of the soybean producing areas of Minnesota. While most products performed well during the 2003 outbreaks, occasional poor performance was reported. It was hypothesized that these problems were related to high temperatures at application and/or the speed at which quickly mortality occurred.
This trial was designed to look at aphid
control and resultant yield differences between insecticide products and rates.
Based on results of previous studies, the products in this trial represent
a range in rapidity (knockdown) and duration of soybean aphid control but
not all labeled products or rates. Additionally, an anti-drift (InterLock)
and a non-ionic surfactant (Preference) adjuvant were evaluated for their
effect on aphid control. In the case of Asana XL, both rates were on the low
side of rate structure with the 6.4 fl. oz./acre in common use for soybean
aphid. In the case of Baythroid, the 2 fl. oz./acre rate was included as a
comparison of control with the the addition of ½ pt./acre of Lorsban 4E to
a low rate of Baythroid. Trimax is a nicotinoid insecticide included in this
trial to test foliar efficacy of this insecticide class. Trimax is not labeled
on soybean.
Site and application information
Cooperators:
Paul Torkelson, Steve Sodeman County: Watonwan, MN Nearest town: St. James,
MN Soil type: Loamy fine sands and fine sandy loams Fertility: By necessity,
this trial was placed into variable soil conditions including Litchfield loamy
fine sands and Darfur fine sandy loams with the respective soil test values
of: pH of 5.5 and 7.7, % O.M of 2.2 and 3.7, Phosphorus (Olsen test) of 15
and 32 ppm, and Potassium of 118 and 153 ppm. Blocks were arranged to account
for this soil variability but soil type differences are reflected in the relatively
high C.V. values for yield.
Beginning
on or near July 18th a large immigration of alatoid (winged) aphids
occurred. Alate populations averaged
nearly 1/plant with associated nymphs causing a rapid increase of populations
(Figure 1).
Tillage: Ridge-till
Cultivar:Pioneer 92B12 (SCN resistant)
Weed control: Burndown - Glyphosate
+ 2,4-D
Post
I – Select + Flexstar+ Harmony (Broadcast)
Post II= Pursuit + Flexstar (10 inch Band)
Row spacing: 30”
Planting date:
Design: Randomized complete block with
4 replications
Plot size: 15’ x 30’ (the center 4 of 6 rows (10’) were treated,
the center 2 of 6 rows were sampled for aphid populations and harvested for
yield.
Application date:
Temperature: 52 F RH: 61.5%
Wind conditions: 0-6.6 mph
Crop stage at application: V13/R4.5 stage soybeans
Crop height at application: 28 inches
Harvested
Insecticide treatments were applied with a Tractor mounted offset boom sprayer (R&D
Sprayers), 8002XR flat fan nozzles on 18-inch spacing, 23 gallons/acre and
35 PSI pressure.
Early season soil moisture was low. Unlike
much of southern
Results and discussion
The design of this experiment should have
favored soybean aphid re-colonization of treated plots from untreated rows
on either side. This was one of very few southwest
Aphid populations at the time insecticides
were applied were barely at treatment threshold
levels and approximately 282 aphids/plant relatively uniformly distributed
across the trial area. Alatoid nymphs were observed at the time of insecticide application. Similar
to observations at some sites in previous years, populations declined at
R 4.5 due to the production of alate aphids. After
2 days after treatment (DAT) populations remained stable until R6 when populations
collapsed due primarily to emigration of aphids from maturing soybean plants.
Population loss from emigration was greater and population rebound was less
in replications to the north side of the trial. This may have been to greater
moisture stress and poorer plant health. Increasingly variable (plant to
plant and replication to replication) aphid populations are reflected in
extremely high c.v. values.
Aphid control and yield results are presented in Table 1.
Table 1. Foliar applied insecticide control of
Soybean Aphid.
Paul
Torkelson farm,
At 2 days after treatment (2 DAT), only
the 1 and 2 pt./acre Lorsban
4E treatments had fewer aphids than untreated plots.
By 6 DAT after treatment all treatments
containing Warrior, Lorsban 4E (1,2
and ½ pt./acre Lorsban 4E+ 2 oz. Baythroid),
and the 2.8 fl. oz./acre rate of Baythroid had
fewer aphids than other treatments. The untreated check, 2 fl.oz/acre
rate of Baythroid, 2.8 fl. os./acre rate of Mustang Max,
5.8 and 6.4 fl. oz/acre rate of Asana XL, and the 1 and 1.5 fl. oz./acre
rate of Trimax rate
had the greatest numbers of aphids. This lack of aphid control was probably not just
due to slow kill because new nymphs were observed
in lesser performing treatments. Additionally, unlike previous studies in
The relative performance of treatments
remained constant through 14 DAT after treatment. Treatments containing
Warrior and Lorsban had the fewest aphids. Both
Trimax rates, the 2.8 fl. oz./acre
rate of Mustang Max, and untreated check had the greatest number of aphids.
The Asana XL, Baythroid and 4 fl oz./acre
Mustang Max rate treatments were intermediate in soybean aphid control.
Rate response within products not as pronounced
as 2002 and 2003 but due to collapse of the aphid populations control ratings
base 14 DAT were not possible. Significant soybean aphid population rebound
was not observed for any treatment during the limited
duration of this trial (14 DAT) and development of the infestation relatively
late season in the growing season.
No difference in control from the 2 fl.
oz./acre rate of Warrior with or without adjuvents
occurred, nor was the 2 oz. rate less effective than the 3.2 fl. oz/acre
rate. The reason (environmental, greater tolerance) for the slower and relatively
lower performance of some of the pyrethroids is
unclear.
No differences in end of season soybean
plant development (height, nodes, pods) were observed (data not shown). Slightly earlier maturity
was observed in some but not all Lorsban 4E treated plots. This was not reflected
in yield.
At the time of population collapse 22
DAT, the untreated checks had accumulated more than 3700 aphid days. However
populations/plant did not exceed 300 aphids/plant in the
check or any treatments and the lack of yield response to aphid control
is not surprising.
Many thanks to,
Mark Anderson and Mellisa Olsem,
Phil Price, for aphid counting assistance. Yield data would not have been
possible without the intrepid SWROC mobile plot spraying and combining crew
of Steve Quiring, Jeff Irlbeck
and Mark Colter.
Asana® XL
® Registered trademark of E.I . du Pont de Nemours and Company
Baythroid®
®Registered trademark of Bayer Crop Science
Lorsban® 4E
® Registered trademark of Dow AgroSciences,
LLC
InterLock™
Agrilliance
LLC
Mustang
Max™
FMC
Corporation
Preference
®
Registered
trademark of Agrilliance LLC
Trimax™ *
Bayer
Crop Science and is not currently labeled on Soybean
Warrior®
® Registered trademark of Syngenta
Crop Protection, Inc.
*not labeled on soybean
The information given in this publication
is for educational purposes only. Reference to commercial products is made with the understanding that no discrimination is intended
and no endorsement by the
Ken Ostlie and B. Potter, U of M (2004)