Soybean Response to Preplant and Foliar‐Applied Potassium Chloride with Strobilurin Fungicides

Abstract

Potassium chloride (KCl) preplant or foliar applied with fungicides to soybean [Glycine max (L.) Merr.] may allow farmers to increase yields when soil K availability is reduced and/or when Septoria brown spot (SBS) (Septoria glycines), frogeye leaf spot (FLS) (Cercospora sojina), or sudden death syndrome (SDS) (Fusarium solani (Mart.) Sacc. f. sp. glycines) are present. Interactions between fertilizer and fungicide management programs have not been examined in the central United States. Our objective was to evaluate the effect of preplant‐ and foliar‐applied KCl alone or combined with pyraclostrobin, azoxystrobin, or azoxystrobin plus lambda‐cyhalothrin on soybean response and severity of SBS, FLS, and SDS. Experiments were conducted in northeastern (Novelty) and southeastern (Qulin) Missouri in 2006 and 2007 on soils with low to medium K. Leaf K concentrations increased 1.4 to 6.1 g kg−1 following preplant KCl compared to nontreated or foliar KCl. Leaf Cl concentrations increased significantly with preplant KCl at Qulin and foliar KCl at R4 at Qulin and Novelty. At Novelty, preplant KCl reduced the severity of SBS and FLS up to 6%, and increased yield 340 kg ha−1, while foliar KCl increased yield 110 kg ha−1 An R4 application of strobilurin fungicides increased yields 230 to 360 kg ha−1 at Novelty. At Qulin, soybean yield increased 390 kg ha−1 with preplant KCl, while there were variable effects of fungicides on the severity of SBS, FLS, or SDS, and no yield increase due to fungicides or foliar KCl. Foliar applications of KCl were no substitute for preplant KCl.