2016 Evaluation of Seed Treatments in South Dakota Soybean Back »

Written collaboratively by Adam Varenhorst, Febina Mathew, Jonathan Kleinjan, and Brady Hauswedell.


Evaluating Soybean Seed Treatments

In South Dakota, the use of insecticide and fungicide seed treatments often occurs in what is considered a prophylactic manner. Although this is technically correct, part of the prophylactic nature of their use is directly related to the lack of management recommendations. There are definite hurdles associated with producing management recommendations for products that are applied prior to planting including determining if pests are even present in a given field. However, many of the insect pests that are targeted by insecticide seed treatments are belowground and require intensive scouting to evaluate. This is further complicated by the current management recommendations that evaluate perceived pest pressure based on rotating a field from grass (e.g., pasture, CRP), applying manure, or having a high value crop (e.g., seed soybean). Although unfavorable due to increased input costs and associated environmental impacts, the prophylactic use of seed treatments are often the most economical option for farmers.

In 2014, the EPA published a document stating that there was a $0.00 benefit associated with the use of insecticide seed treatments in Midwestern soybean. However, shortly after the report was published an independent group evaluated the same data and found that on average there is a 2% yield benefit per acre associated with the use of insecticide seed treatments.

SDSU Extension Research

Soybean Management Practices
At SDSU, we were interested in determining why there is a 2% benefit associated with the use of insecticide seed treatments. That is, we are focused on determining when this benefit is present so that new management recommendations can be produced for South Dakota soybean farmers. The objective of our study was to evaluate the effects that location, planting date, and seeding rate have on the efficacy of a fungicide and a fungicide + insecticide combination seed treatments in South Dakota. To determine if these factors impacted the utility of seed treatments we evaluated stand counts, insect pest pressure, and diseases pressure throughout the 2016 growing season.

Testing Locations
At the end of the season, yield was collected from each plot. The four locations that were selected included: Northeast Research Farm, Volga Research Farm, Brookings Research Farm, and Southeast Research Farm (Figure 1). The commercially available soybean varieties that were used for this experiment varied in maturity for each location. In 2016, plots were planted during the first week of May and first week of June with the exception of the Southeast Research Farm where soybean were planted two weeks later for both May and June (Table 1).

Figure 1. Plot locations used for the study.

1) Northeast Research Farm
2) Volga Research Farm
3) Brookings Research Farm
4) Southeast Research Farm
 

2016 Research Findings

Soybean Yield
Data from the 2016 growing season indicated that location, planting date, and seeding rate significantly impacted soybean yield. The early planting date (May) had increased yields at the Volga Research Farm (Table 4), Brookings Research Farm (Table 6), and Southeast Research Farm (Table 3) when compared to the late planting date (June) for each location. The one exception to this was observed at the Northeast Research Farm (Table 5), where the June planted soybean had increased yields when compared to the earlier May planting. This was most likely due to the dry conditions that were present during the flowering period of the early planted soybeans at that location. Although yield was variable among seeding rates there were instances where lower seeding rates yielded similar or better than higher seeding rates. Additionally, significant differences were observed infrequently between the untreated and fungicide + insecticide seed treatment. However, the fungicide + insecticide treatment was numerically greater than the untreated plots 38% of the time in 2016.

Disease Evaluation
We also evaluated soybean plants for root rot. From the outer rows of each plot, soybean plants were sampled at 14 days post emergence. A total of 10 randomly selected plants were sampled from each plot. The 10 plants were rated as a whole to determine the percent of root rot lesions per plot (Table 2). Higher disease ratings correspond to more of each root affected by root rot. When comparing disease severity, there were significant differences between location. There were also significant differences in disease severity between planting dates at Brookings and the Northeast farm. The Southeast farm and Volga farm did not show differences in disease severity between the two planting dates. Different seeding rates had no effect on disease severity on each plant sampled. However, seed treatments were significant for both planting dates at the Northeast farm and Southeast farm; Brookings and Volga observed significant differences in just the late planting dates.

The Bottom Line

Yield was similar between the different seeding rates at each location, which indicates that lower seeding rates could be more profitable. Yield varied across the regions and differences that were observed may be due to multiple different abiotic factors affecting each location, including soil properties and rainfall amounts. Because of the lack of management recommendations, seed treatments are often being used when disease and insect pressure are low or not present at all. When both insects and diseases are absent from a field, seed treatments are an additional input cost that cannot be recovered. This explains why a seed treatment may increase yield in one field and not another. This phenomenon is observed when the yield of each treatment at the Southeast Farm (Table 3) is compared to each treatment at the Volga Farm (Table 4). The Southeast Farm had higher disease severity present than Volga, which resulted in plots with seed treatments usually yielding higher than the untreated plots at the Southeast Farm when compared to Volga. The results from the first year of this two-year study indicate that planting earlier in the season will likely result in higher yields and that producers should consider lower seeding rates. That being said seeding rates and seed treatment uses may need to be based on regions within SD instead of broad regional recommendations. In 2016, a positive return on the seed treatment investment was only observed at the Southeast Research Farm.

Acknowledgements

Funding for this study was provided by South Dakota Soybean Research and Promotion Council and SDSU Extension.


Appendices
 

Table 1. 2016 planting dates for soybean at each location.
Location Early Planting Late Planting
Northeast Research Farm 3-May 1-Jun
Volga Research Farm 2-May 1-Jun
Brookings Research Farm 3-May 2-Jun
Southeast Research Farm 19-May 22-Jun

 

Table 2. Rating determined by assessing root rot lesions at each S.D.location.
  Untreated Fungicide
seed treatment
Fungicide + insecticide
seed treatment
Beresford Early 16.4 11.4 11.2
Late 16.3 13.5 12.9
Brookings Early 13.0 12.4 11.3
Late 17.9 12.8 12.0
South Shore Early 17.6 10.2 9.2
Late 20.7 14.4 14.7
Volga Early 12.0 13.2 11.9
Late 15.5 11.5 11.1

 

Table 3. Southeast Research Farm May and June planting date data.
Location/ Date1 Seeding Rate
(thousands)2
Yield by treatment (bushels/acre)3
Untreated Fungicide Fungicide +
Insecticide
Southeast 60 74.3±1.5 73.7±1.6 76.1±1.4
May a 80 72.9±1.8 73.2±1.2 72.0±1.0
  100 69.2±1.3b 72.3±0.8ab 75.6±2.1a
  120 69.4±2.4 74.8±2.2 71.6±1.3
  140 72.7±2.2 73.4±1.3 75.7±1.3
  160 73.2±1.3 71.3±1.3 71.7±1.0
  180 73.1±1.3 74.6±1.8 73.5±2.1
 
Southeast 60b 59.5±5.2 62.9±1.6 64.2±1.9
June b 80ab 60.3±3.0 63.7±3.8 66.5±3.8
  100a 66.0±2.3 67.0±3.2 68.4±2.4
  120ab 60.2±4.1 64.2±2.5 65.9±1.9
  140a 68.7±3.2 64.8±3.5 69.0±2.3
  160a 61.8±3.7b 68.5±1.7ab 71.0±2.3a
  180a 68.2±2.2 66.1±2.7 68.5±2.8
1 Letters represent significant differences among planting dates (column 1).
2 Letters represent significant differences among seeding rates by planting date (column 2).
3 Letters represent significant differences among treatments for a given seeding rate (row).

 

Table 4. Volga Research Farm May and June planting date data.
Location/ Date1 Seeding Rate
(thousands)2
Yield by treatment (bushels/acre)3
Untreated Fungicide Fungicide +
Insecticide
Volga 60b 81.6±1.5 80.1±1.2 79.9±1.0
May a 80a 84.5±1.9 82.6±1.2 81.5±1.8
  100a 83.2±1.3 84.0±1.0 83.9±1.7
  120a 82.9±2.0 82.7±1.4 83.7±1.5
  140a 84.4±1.2 81.9±1.8 82.0±1.3
  160a 84.0±1.4 82.1±1.2 82.2±1.8
  180a 82.3±1.3 83.2±0.9 84.2±1.6
 
Volga 60b 64.9±1.3 64.3±1.8 68.7±1.2
June b 80ab 67.1±1.0 71.0±1.0 68.0±1.4
  100a 69.5±0.8 65.3±0.8 66.5±0.5
  120a 68.8±1.8 68.5±0.9 68.4±0.8
  140a 67.6±1.1a 66.6±0.9ab 66.6±1.7b
  160a 67.5±1.0 70.2±1.0 67.0±0.8
  180a 67.2±1.9a 68.1±1.2b 66.4±0.7b
1 Letters represent significant differences among planting dates (column 1).
2 Letters represent significant differences among seeding rates by planting date (column 2).
3 Letters represent significant differences among treatments for a given seeding rate (row).

 

Table 5. Northeast Research Farm May and June planting date data.
Location/ Date1 Seeding Rate
(thousands)2
Yield by treatment (bushels/acre)3
Untreated Fungicide Fungicide +
Insecticide
Northeast 60a 63.4±2.2 62.8±4.0 59.7±2.0
May b 80b 58.0±2.5 57.3±2.6 58.0±1.7
  100bcd 55.6±1.4ab 58.3±2.6a 53.5±1.7b
  120bc 57.3±3.0 57.6±2.7 55.5±2.6
  140bcd 54.6±1.8 53.9±0.9 56.7±2.7
  160d 50.4±1.9 54.6±2.4 53.7±2.6
  180cd 54.6±3.1 53.1±1.8 54.5±1.8
 
Northeast 60 70.4±2.3 69.7±1.6 70.7±1.0
June a 80 67.8±1.3b 71.5±1.4a 69.6±0.7ab
  100 69.6±1.7 70.1±1.3 68.8±1.3
  120 67.9±0.6 71.2±1.1 69.8±2.5
  140 70.2±2.3 69.7±1.4 68.7±1.7
  160 69.5±0.9 70.5±1.0 69.3±2.0
  180 67.4±1.9 70.7±1.8 68.7±2.0
1 Letters represent significant differences among planting dates (column 1).
2 Letters represent significant differences among seeding rates by planting date (column 2).
3 Letters represent significant differences among treatments for a given seeding rate (row).

 

Table 6. Brookings Research Farm May planting date data.
Location/ Date1 Seeding Rate
(thousands)2
Yield by treatment (bushels/acre)3
Untreated Fungicide Fungicide +
Insecticide
Brookings 60ab 70.4±2.5 73.9±2.3 70.8±3.6
May a 80b 70.1±1.0 69.6±1.9 71.6±2.5
  100a 73.8±2.2 75.0±2.9 72.7±2.0
  120ab 76.2±0.4a 75.4±1.4b 68.5±2.8c
  140ab 73.1±1.6 73.8±1.5 72.2±1.6
  160ab 73.6±1.1ab 71.2±1.0b 75.1±1.1a
  180a 74.5±1.0 75.5±1.6 73.3±1.7
 
Brookings 60d 51.2±2.4 48.5±2.3 46.1±1.0
June b 80c 54.3±2.1ab 55.8±1.5a 50.1±1.7b
  100c 52.1±1.3 55.9±1.4 51.8±1.2
  120b 56.7±1.6 57.2±1.1 56.5±0.9
  140b 58.8±3.3 56.7±2.9 54.8±1.2
  160ab 58.2±2.0 57.4±0.8 58.8±1.0
  180a 59.1±2.0 61.9±1.6 60.9±1.4
1 Letters represent significant differences among planting dates (column 1).
2 Letters represent significant differences among seeding rates by planting date (column 2).
3 Letters represent significant differences among treatments for a given seeding rate (row).

 

References:

  • Bailey, W., C. DiFonzo, E. Hodgson, T. Hunt, K. Jarvi, B. Jensen, J. Knodel, R. Koch, C. Krupke, B. McCornack, A. Michel, J. Peterson, B. Potter, A. Szczepaniec, K. Tilmon, J. Tooker, and S. Zukoff. 2015. The effectiveness of neonicotinoid seed treatments in soybean. Purdue University Extension.
  • Mitchell, P. D. 2014. The value of neonicotinoids in North American Agriculture: A meta-analysis approach to estimating the yield effects of neonicotinoids. AgInformatics 1-64.
blog comments powered by Disqus

Sign Up For Email!