Effect of prophylactic foliar fungicide application on soybean yield and seed quality in Mississippi
The MSPB funds myriad projects each year. These funded projects are designed to provide information that Mississippi soybean farmers can use to improve/enhance soybean production and economic return in their operations. Below is a summary of results from two such projects that were published in the online journal Crop, Forage & Turfgrass Management (CFTM). The research summarized in these articles was conducted as part of the MSU-ES SMART program (Projects 36-2017 and 36-2018) that is conducted under the direction of MSU-ES Soybean Specialist Dr. Trent Irby.
The articles are titled “Evaluation of fungicide application timing on soybean yield, quality, and economic return” [Paper 1 (CFTM 2021;7:e20102)] and “Evaluation of soybean grain quality and yield across various row spacings, planting dates, and fungicide programs” [Paper 2 (CFTM 2023;9:e20201)], and both are authored by Floyd et al. They present results from research that was conducted in 2017 and 2018 in Mississippi to determine the optimal timing for the application of prophylactic fungicides to soybean in the absence of disease, and the resulting impact on soybean yield, seed quality, and partial economic return to the practice. A summary of the conduct of this research and its results follow.
• Irrigated field experiments [Paper 1] were conducted in 2017 and 2018 at Starkville [33°47' N lat.] on a fine sandy loam soil and at Stoneville [33°40' N lat.] on a Sharkey clay soil. In 2018, a nonirrigated experiment [Paper 2] was conducted at Brooksville [lat. 33°26' N lat.] on a silty clay soil, and two irrigated experiments were conducted at Starkville on a fine sandy loam soil. In all studies, prophylactic foliar fungicide applications were made regardless of disease presence; in these studies, disease pressure was light to non-existent.
• Indeterminate MG IV soybean varieties were used in both years at all locations. All varieties were selected based on optimal ratings against foliar diseases that commonly occur in Mississippi.
• Results reported in Paper 1 are from studies that were planted in early to mid-May, whereas results reported in Paper 2 are from studies that were planted in late April/early May [early planting] and late May [late planting].
• Results reported in Paper 1 are from studies planted at 130,000 seeds/acre in 38-in.-wide rows.
• Results reported in Paper 2 are from studies that had 130,000 seeds/acre planted in rows that were 38, 30, and 15 in. wide.
• Three fungicide products were used in all studies. They were Quadris [azoxystrobin–FRAC code 11], Quadris Top SBX [azoxystrobin + difenoconazole–FRAC codes 11+3], and Priaxor [fluxapyroxad + pyraclostrobin–FRAC codes 7+11] + Domark 230ME [tetraconazole–FRAC code 3].
• Studies reported in Paper 1 had each of the three foliar fungicides ground-applied at soybean stages R3, R4, R5, R6, and R3+R5. Studies reported in Paper 2 had each foliar fungicide ground-applied at soybean stage R4 to all treatments.
• In all studies, partial returns to fungicide applications were calculated, and included price discounts for seed damage. A market price of $8–$10/bu. was used for all economic analyses.
• Foliar fungicide application timing had no effect on soybean seed yield [Paper 1].
• Results reported in Paper 1 showed that both of the multi-mode-of-action fungicide products resulted in significantly greater yields than that from the nontreated control [62.1 and 62.3 bu/acre vs. 59.8 bu/acre], but the yield differences were small. Use of Quadris SBX resulted in the most profit increase using the $8-$10/bu. market price.
• Results reported in Paper 2 showed a) no interaction effect among row spacing, planting date, and fungicide product on soybean seed yield, b) yield of early-planted soybean [60.0 bu/acre] was greater than the yield of 51.1 bu/acre from the late planting, c) foliar fungicide application did not improve quality of harvested seed, d) soybean seed harvested from the late planting had less damage [4.8 score] than those harvested from the early planting [21 score], and e) the higher yield from the early planting resulted in a greater net return above fungicide cost.
Takeaway. 1) Timing of prophylactic foliar fungicide applications to soybeans based on reproductive stage [R3 to R6] did not affect soybean yield [Paper 1]. 2) Multi-mode-of-action fungicides only slightly improved soybean yield compared to no fungicide application [Paper 1]. 3) Application of Quadris Top SBX [a multi-mode-of-action product] resulted in the greatest return to fungicide application at a commodity price of $8-$10/bu. 4) Only planting date significantly affected overall soybean seed yield [Paper 2]. 5) Row spacing and fungicide product used in these studies did not result in grain quality differences. 6) Early-planted soybean had lower quality of harvested seed, but its higher yield overcame the lower economic value of the harvested product [Paper 2]. 7) Finally, and most importantly, a) foliar fungicides should not be prophylactically applied to soybean for the purpose of improving seed quality, b) in the absence of foliar diseases, prophylactic application of foliar fungicides should be based on an expected small yield increase at best, coupled with the price of the fungicide product that is used, and c) producers are encouraged to remember that the continued use of foliar fungicides when they may not be needed in the absence of disease pressure will hasten pathogen resistance to those fungicides.
Composed by Larry G. Heatherly, Feb. 2023, larryh91746@gmail.com.