Effect of Mid-Season Foliar Fungicide and Foliar Insecticide Applied Alone and In-Combination on Soybean Yield
Sin Joe Ng, Laura E. Lindsey, Andrew P. Michel, and Anne E. Dorrance
Due to the relatively low cost of foliar insecticide, farmers frequently tank-mix insecticide with fungicide. The objective of this study was to evaluate the effect of mid-season foliar fungicide and insecticide treatments on soybean grain yield, applied alone or in combination. Foliar treatments applied at the R3 growth stage included: 1) non-treated control, 2) fungicide, 3) insecticide, 4) fungicide + insecticide, 5) fungicide + insecticide (applied separately), 6) fungicide + crop oil, 7) insecticide + crop oil, and 8) fungicide + insecticide + crop oil.
QUICK TAKE-AWAY
- Soybean treated with fungicide + insecticide tank-mixed did not yield differently than soybean treated with fungicide and fungicide + crop oil.
- Fungicide treatments increased soybean yield at 4 of 12 site-years, and at three of these locations, brown spot and frogeye leaf spot disease were ≥ 6.5% leaf area affected.
- There was no yield response associated with insecticide treatment due to sub-threshold insect defoliation levels at the time of insecticide treatment.
- Application of fungicide alone, insecticide alone, or in tank-mix did not improve yields when insects or foliar diseases were not present at threshold levels.
Methods. The study was conducted in 2015 and 2016 at six on-farm locations each year in Clinton, Henry, Marion, Mercer, Preble, and Sandusky Counties in Ohio. Fungicide and insecticide treatments applied at the R3 growth stage included: 1) non-treated control, 2) fungicide, 3) insecticide, 4) fungicide + insecticide, 5) fungicide + insecticide (applied separately), 6) fungicide + crop oil, 7) insecticide + crop oil, and 8) fungicide + insecticide + and crop oil. All combinations were tank-mixed except treatment 5 where fungicide + insecticide were applied using separate tanks. The fungicide was Priaxor® applied at 4 fl oz/acre, the insecticide was Warrior II with Zeon Technology® at 1.92 fl oz/acre, and the crop oil was Superb®HC at 1 pt/acre.
Data for disease and insect defoliation ratings were collected at each location one week before treatment and four weeks after treatment at the R6 soybean growth stage. Main diseases present include brown spot and frogeye leaf spot.
Fungicide only treatment compared to fungicide applied with insecticide and/or crop oil results. The treatments of fungicide + insecticide, fungicide + insecticide applied separately, fungicide + crop oil, and fungicide + insecticide + crop oil resulted in grain yield that was not statistically different than the fungicide treatment (Table 1). These results indicated that there was no yield benefit associated with combining fungicide with insecticide, crop oil, and insecticide + crop oil when insect pressure and LAA by insect defoliation were sub-threshold. Use of foliar insecticide (especially repeated use of a single chemical or mode of action) is discouraged when insect populations are below the economic threshold level due to concerns of insecticide resistance from overuse (Elzen and Hardee, 2003; Hodgson et al., 2012).
| Treatment | Clinton | Henry | Marion | Mercer | Preble | Sandusky |
|---|---|---|---|---|---|---|
| 2015 | ||||||
| Fungicide | 52.6 | 56.2 | 60.1 | 61.0 | 62.0 | 61.9 |
| Fungicide + insecticide | -3.7 | +0.5 | -0.3 | +4.3 | +3.0 | +0.7 |
| Fungicide + insecticide (separate) | -0.8 | +3.2 | +1.2 | -2.4 | +0.8 | +8.5 |
| Fungicide + crop oil | +0.1 | +1.4 | +0.7 | +3.2 | +2.9 | +5.2 |
| Fungicide + insecticide + crop oil | -0.1 | +0.6 | +2.0 | +2.5 | +4.0 | +5.4 |
| 2016 | ||||||
| Fungicide | 58.3 | 58.1 | 54.5 | 61.5 | 59.4 | 56.9 |
| Fungicide + insecticide | +0.1 | +1.1 | -0.3 | -1.3 | +3.6 | -1.0 |
| Fungicide + insecticide (separate) | +3.5 | +2.8 | -2.5 | -2.2 | +1.0 | +0.1 |
| Fungicide + crop oil | +0.6 | +1.0 | +1.9 | +1.1 | +4.0 | -2.7 |
| Fungicide + insecticide + crop oil | +3.8 | +1.3 | +0.6 | -2.8 | +0.2 | +0.5 |
Effect of fungicide on soybean yield and disease results. During 2015, fungicide treatment increased yield by 7.9, 6.3, and 4.4 bu/acre when compared to the non-treated control in Clinton, Marion, and Preble Counties, respectively (Table 2). In 2016, the fungicide treatment increased yield by 7.1 bu/acre at the Mercer County location. Yield increases were associated with brown spot (Figure 1) and frogeye leaf spot (Figure 2) disease which were more severe in 2015 compared to 2016 likely due to greater precipitation creating a favorable environment for disease development.
| Treatment | Clinton | Henry | Marion | Mercer | Preble | Sandusky |
|---|---|---|---|---|---|---|
| 2015 | ||||||
| Non-treated control | 44.8 | 56.3 | 54.1 | 59.1 | 59.0 | 60.2 |
| Fungicide only |
+7.9 |
+0.6 |
+6.3 |
+3.5 |
+4.4 |
+4.3 |
| Insecticide only | +0.5 | +0.3 | +4.2 | +0.4 | +3.4 | +2.3 |
| 2016 | ||||||
| Non-treated control | 59.5 | 56.7 | 53.3 | 55.0 | 55.1 | 53.3 |
| Fungicide only | -0.9 | +1.9 | +2.2 |
+7.1 |
+6.3 | +1.0 |
| Insecticide only | -0.8 | +0.4 | -1.0 | +3.1 | +0.7 | +0.8 |
 |
 |
Effect of insecticide on insects and yield. Insecticide applications did not influence soybean grain yield compared to the non-treated control. The lack of yield response was likely due to sub-threshold defoliation and insect populations below the economic threshold level at the time of treatment. The highest percentage of leaf area affected by insect defoliation was 11%. The maximum levels of defoliation that can be tolerated by soybean without significant yield loss was 40% from seedling to R1 (initial bloom), 15% from R1 to R5 (initial pod fill), and 25% from R5 to maturation (Hunt and Jarvi, 2007). Soybean aphids were below the economic threshold of 250 aphids/plant during the R1-R5 soybean growth stages (Hodgson et al., 2012).
Bean leaf beetle pod damage at the Marion County location in 2015 was 13-18% while pod damage was 9-37% at Henry, Marion, and Sandusky County in 2016. Yield reductions likely occurred due to soybean pod damage by bean leaf beetle at locations with 10-15% pod injury (Hammond et al., 2014). However, there was no yield benefit associated with the R3 insecticide treatment because second generation bean leaf beetle populations began in late August through early September and the insecticide applied at the R3 growth stage (late July) likely did not have sufficient residual activity to control pests (Hammond, 1996; Hammond et al., 2014).
Recommendations. In this two-year study, no significant yield response occurred when insecticide was applied due to insect populations below the economic threshold level and sub-threshold defoliation at the time of insecticide treatment. However, at the end of the growing season, the number of bean leaf beetles and pod injury was high at 4 out of 12 site-years. Treatment of insecticide at the R3 soybean growth stage (late July) was too early to be effective against bean leaf beetle which generally appear during late August through early September in Ohio (Hammond et al., 2014). Despite the low cost of tank-mixing insecticide with fungicide, this practice is not recommended unless insect pests and/or leaf defoliation is at the economic threshold due to concerns of insecticide resistance (Hodgson et al., 2012).
References
Elzen, D.B., and D.D. Hardee. 2003. United States Department of Agriculture-Agricultural Research Service research on managing insect resistance to insecticides. Pest Manag. Sci. 59:770-776. doi: 10.1002/ps.659
Hodgson, E.W., B.P. McCornack, K. Tilmon, and J.J. Knodel. 2012. Management recommendations for soybean aphid (Hemiptera:Aphididae) in the United State. J. Integrated Pest Management. 3:1-10.
Hammond, R.B. 1996. Residual activity of lambda-cyhalothrin against bean leaf beetle (Coleoptera: Chrysomelidae) in soybeans. J. Agric. Entomol.13:365-373.
Hammond, R.B., A. Michel, and J.B. Eisely. 2014. Bean leaf beetle on soybean. Ohio State Univ. Ext. Fact Sheet ENT-23. Ohio State Univ., Columbus, OH. http://ohioline.osu.edu/factsheet/ENT-23 (accessed 28 Apr. 2017).
Hunt, T. and K. Jarvi. 2007. Evaluating soybean defoliation and treatment need. University of Nebraska-Lincoln. CropWatch. Online publication http://cropwatch.unl.edu/evaluating-soybean-defoliation-and-treatment-need (accessed 26 May 2017).
Acknowledgements
- Research funded by Ohio Soybean Council
- Fungicide donated by BASF.
- Salary and research support provided in part by state and federal funds appropriated to the Ohio Agricultural Research and Development Center (OARDC) and Ohio State University.
Originally published: Ng, S.J.; L.E. Lindsey, A.P Michel, and A.E. Dorrance. 2018. Effect of mid-season foliar fungicide and foliar insecticide applied alone and in-combination on soybean yield. Crop, Forage, and Turfgrass Management.