Soybean yield can be affected by various pests, including weeds, diseases, and insects. The economics of soybean production have changed in the last decade, so more attention is being focused on saving soybean yield from these factors through pesticide applications. A three-year study was conducted at the East Central Experiment Field in Ottawa to evaluate soybean response to preemergence herbicides with residual weed control, foliar fungicides, and foliar insecticides.
Procedures
The experimental site was located on a Woodson silt loam. Soybean were no-till planted on 30-in. rows into sorghum stubble in 2010, corn stubble in 2011, and soybean stubble in 2013. Soybean were planted on June 21, 2010; June 9, 2011; and May 29, 2013, with soybean varieties AG4606, S47-R3, and S46-G9, respectively.
Treatments included: (1) burndown herbicide without residual; (2) burndown herbicide with residual; (3) burndown herbicide with residual + foliar fungicide at R3; and (4) burndown herbicide with residual + foliar fungicide and insecticide at R3.
Common waterhemp weed control ratings were evaluated at the V4 soybean growth stage. All treatments received 0.75 lb a.i./a glyphosate application at the V4 soybean growth stage. Fungicide and insecticide treatments were applied at the R3 reproductive stage (beginning of pod formation). No significant foliar disease pressure was observed in the trial across all three years, but some insect pressure was noted at the time of the R3 insecticide application. In 2010, one bean leaf beetle and one stinkbug per 100 feet of soybean row were noted at the time of the R3 application. In 2011, two bean leaf beetles and one corn earworm per foot of row were observed at the R3 stage. In 2013, two green clover worms and two grasshoppers per 100 feet of row were observed at R3.
Results
Soybean in 2010 were planted at a site with glyphosate-susceptible common waterhemp. As a result, excellent weed control was received across all herbicide treatments, and no significant differences were observed in soybean yield between herbicide treatments in 2010. In 2011 and 2013, soybean were planted at a site with glyphosate-resistant common waterhemp. Consequently, weed control ratings at the V4 growth stage were poor for the glyphosate and the glyphosate + 2,4-D burndown treatment compared with treatments that included saflufenacil (the active ingredient in Sharpen) and pyroxasulfone (the active ingredient in Zidua, Fierce, and Anthem).
Treatments that contained saflufenacil in the burndown mixture provided control of small emerged common waterhemp at the time of soybean planting, and the residual of pyroxasulfone maintained excellent weed control through the first 6 weeks of the growing season. Although there was a weed control difference in 2011 among herbicides with and without residual, soybean yield did not differ. In 2013, however, there was a 4.6 bu/a advantage with the residual herbicide treatment due to reduced weed competition.
Only trace levels of frogeye leaf spot disease were present in 2010 and 2013, whereas no foliar disease was observed in 2011. In 2010, soybean treated with a fungicide resulted in a 5.1 bu/a yield increase over the untreated check. Insect pressure was below the treatment threshold in 2010, but the addition of an insecticide at the R3 growth stage significantly increased soybean yield by 2.4 bu/a over soybean treated with a fungicide alone. In 2011, insect pressure reached the treatment threshold of one corn earworm per ft of soybean row, but no significant yield increase was observed with the addition of an insecticide. In 2013, insect pressure was low, and the addition of an insecticide did not significantly increase yield.
Summary
A three-year study was conducted to evaluate soybean yield response to herbicides with preemergence residual weed control, foliar fungicides, and foliar insecticides. Preemergence herbicides provided excellent control of glyphosate-resistant common waterhemp, resulting in a significant soybean yield increase of 4.6 bu/a in 2013. Soybean yield was significantly increased with the addition of a foliar fungicide and foliar fungicide + insecticide applied at the R3 growth stage in 2010. Yield increases of 5.1 and 7.5 bu/a were observed for the fungicide and fungicide + insecticide treatments, respectively.
|
Effect of herbicides, foliar fungicides, and foliar fungicides on soybean yields and common waterhemp control: Ottawa, 2010-2013 |
||||
|
Year |
Preemergence herbicide and rate (lb a.i./acre) (All plots also received a postemergence glyphosate treatment at V4) |
Treatment at R3 |
Common waterhemp % control |
Soybean yield (bu/acre) |
|
2010 |
Glyphosate (0.75) |
-- |
96.7 |
45.2 |
|
|
Glyphosate (0.75) + saflufenacil* (0.02) + imazethapyr* (0.06) |
-- |
92.3 |
44.9 |
|
|
Glyphosate (0.75) + saflufenacil (0.02) + imazethapyr (0.06) |
Pyraclostrobin (fungicide) |
90.8 |
50.0 |
|
|
Glyphosate (0.75) + saflufenacil (0.02) + imazethapyr (0.06) |
Pyraclostrobin (fungicide) + zeta-cypermethrin (insecticide) |
96.7 |
52.4 |
|
|
LSD (0.05) |
|
8.9 |
2.1 |
|
2011 |
Glyphosate (0.75) |
-- |
15.0 |
24.6 |
|
|
Glyphosate (0.75) + saflufenacil (0.02) + imazethapyr (0.13) |
-- |
88.3 |
23.5 |
|
|
Glyphosate (0.75) + saflufenacil (0.02) + imazethapyr (0.13) |
Fluxapyroxad (fungicide) + pyraclostrobin (fungicide) |
89.7 |
24.8 |
|
|
Glyphosate (0.75) + saflufenacil (0.02) + imazethapyr (0.13) |
Fluxapyroxad (fungicide) + pyraclostrobin (fungicide) + alpha-cypermethrin (insecticide) |
92.7 |
26.3 |
|
|
LSD (0.05) |
|
12.5 |
3.4 |
|
2013 |
Glyphosate (0.75) + 2,4-D (0.50) |
-- |
6.7 |
29.3 |
|
|
Glyphosate (0.75) + saflufenacil (0.02) + imazethapyr (0.13) |
-- |
89.3 |
33.8 |
|
|
Glyphosate (0.75) + saflufenacil (0.02) + imazethapyr (0.13) |
Fluxapyroxad (fungicide) + pyraclostrobin (fungicide) |
93.3 |
36.4 |
|
|
Glyphosate (0.75) + saflufenacil (0.02) + imazethapyr (0.13) |
Fluxapyroxad (fungicide) + pyraclostrobin (fungicide) + alpha-cypermethrin (insecticide) |
93.3 |
35.7 |
|
|
LSD (0.05) |
|
9.9 |
3.3 |
Note: In 2010, the common waterhemp population was susceptible to glyphosate. In 2011 and 2013, the common water hemp population was resistant to glyphosate.
* Saflufenacil is the active ingredient in Sharpen. Imazethapyr is the active ingredient in Zidua, Fierce, and Anthem.
Source: Kansas Field Research 2014, SRP-1102 http://www.ksre.ksu.edu/bookstore/pubs/SRP1102.pdf
Doug Shoup, Southeast Area Crops and Soils Specialist
dshoup@ksu.edu
Eric Adee, East Central Experiment Field, Agronomist-in-Charge
eadee@ksu.edu
Tags: