Fungicide-insecticide application increased soybean yield by 2.4 bu/acre across all sites under low disease pressure.
Enhanced fertility did not significantly increase yield across these trials.
Soybean varieties differed in their response to fungicide-insecticide application in 2023 at some locations but not consistently across years.
Introduction
Corn hybrids are known to respond differently to fungicide and fertility management, but less is known about individual soybean variety response differences.1 Previous Agronomy in Action soybean management research trials in 2021 and 2022 have shown a positive response in soybean yield to fungicide application yet response to fertilizer was lower. Soybean management trials in 2022 showed similar responses to fungicide or fertility treatments across ten varieties evaluated. Trials were repeated in 2023 to further test varietal yield response to a fungicide-insecticide combination and enhanced fertility.
Soybean Management Trial Details
Research trials were conducted at nine Agronomy In Action sites in 2023. Replicated trials were designed to evaluate response to fungicide-insecticide, enhanced fertility and the combination of the two. A standard fertility practice was applied across the entire trial based on the host farmers’ normal fertility program and additional fertilizer was applied at time of planting to specified strips within the trial. Enhanced fertility strips consisted of the baseline fertilizer in combination with NACHURS Triple Option® at 15 gal/ac (22 lbs/ac P2O5, 29 lbs/ac K2O, and 2 lbs/ac S) and AVAIL® T5 additive (1% of total tank mix) applied through the planter. Planter fertilizer applications were applied using a 2×2×2 placement to provide nutrients in proximity of developing roots while avoiding direct contact with seed and potential germination issues from high salt content. Higher-than-normal starter fertilizer rates were meant to mimic zone fertilizer placement used in strip-till or other precision placement practices.
To test for varietal response to fungicide-insecticide and fertility, six varieties with ranging agronomic characteristics, disease tolerance scores, and herbicide tolerance traits (Enlist E3® soybeans and XtendFlex® soybeans) were selected for each maturity group (MG) region. Soybean varieties were blocked together and split into check, fungicide-insecticide, fertilized, and fungicide-insecticide + fertilized plots. Fungicide-insecticide plots received a broadcast application of Miravis® Neo fungicide at a rate of 13.7 oz/acre and Endigo® ZCX at 4 oz/ac at the R3 growth stage.
Enhanced Fertility Responses
Janesville, WI was the only site out of the nine testing locations that observed a significant response to adding incremental fertilizer (1.8 bu/ac) alone. Six of the nine locations had an average increase of 1.1 bu/ac from pairing extra fertility with fungicide-insecticide applications when compared to fungicide-insecticide alone, but none of the increases were statistically significant. However, the small increases from combining extra fertility with fungicide-insecticide was enough to get a significant response over the base fertility plots at Blue Earth, MN (2.3 bu/ac) and Clinton, IL (2.3 bu/ac) when there was not a significant response from either input alone. Both Clinton and Blue Earth sites had relatively high soil phosphorous (P) levels, but medium to low potassium (K) levels (<200 ppm) as well as higher yields of 96 and 75 bu/ac respectively, that would have demanded more nutrients. Overall, response to incremental fertility was infrequently observed, similarly to trials done in 2022.
Fungicide/Insecticide Response
Averaged across all locations and fertility programs there was a 2.4 bu/ac response to R3 fungicide-insecticide applications (Graph 1), although responses ranged from 0.7 up to 5.1 bu/ac depending on location (Graph 2). Similar fungicide responses of 3.7 bu/ac and 1.3 bu/ac were observed in 2021 and 2022 Agronomy In Action trials respectively. No notable insect pressure observed at any of the locations in 2023. Although disease and insect pressure was generally low at all sites in 2023, delayed plant senescence within treated plots was observed at many locations which likely extended pod fill and contributed to yield gains (Figure 1).
Figure 1. Delayed leaf senescence in plots where Miravis® Neo fungicide was applied (left) compared to the untreated control (right) at Clinton, IL, 2023.Variety Response
Individual variety responses to fungicide-insecticide tank mixes ranged from 0.8 up to 5.5 bu/ac when averaged across sites with similar relative maturity groups (Table 1). In 2023 there were some individual varieties that increased yields from fungicide-insecticide statistically more than other varieties when averaging across testing locations, although yield response by variety varied within individual locations. For example, GH1993XF brand, which was one of the overall lowest responding varieties, on average was also the most responsive variety at the Grundy Center, IA location. In addition, GH1762XF brand which responded significantly more than other varieties in 2023 was one of the lesser responsive varieties in 2022 where GH1973E3S brand was the more responsive variety. When averaging across two years of testing, overall responsiveness of varieties was similar. Since insecticide was applied in 2023, but not 2022, there is a chance across year comparisons are biased by insect feeding. While varietal differences in fungicide-insecticide response may appear to sometimes exist, we have yet to see a single variety that consistently responds more frequently or at a higher magnitude over locations or years.
Conclusions
Fungicide-insecticide applications increased soybean yields by 2.4 bu/ac on average across nine Agronomy In Action sites with low disease pressure in 2023. Differential varietal response to fungicide-insecticide application was not consistent across years. Overall fungicide response was not significantly increased with enhanced fertility. Enhanced fertility by itself rarely increased yields. If base soil fertility levels are sufficient, there is a much higher opportunity for return on investment with fungicide-insecticide applications rather than supplying incremental fertilizer to soybeans.
Reference:
1Kandel, Y.R. C. Hunt, K. Ames, N. Arneson, C. Bradley, E. Byamukama, A. Byrne, M.I. Chilvers, L.J. Giesler, J. Halvorson, D. Hooker, N.M. Kleczewski, D. K. Malvick, S. Markell, B. Potter, W. Pedersen, D. L. Smith, A. U. Tenuta, D. R. P. Telenko, K. A. Wise, and D. Mueller. 2021. Meta-Analysis of Soybean Yield Response to Foliar Fungicides evaluated from 2005 to 2018 in the United States and Canada. Plant Disease. 105: 1382-1389
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