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Soil Properties' Role in Stem Canker Infection of Soybean

USDA-ARS, Nat. Sedimentation Lab., Oxford, MS 38566

^* Corresponding author.

Stem canker [Diaporthe phaseolorum (Cke & Ell.) Sacc. var. caulivora Athow and Caldwell] is a destructive disease of soybean [Glycine max (L.) Merr.] that can unpredictably increase from negligible amounts to near total infestation within a year. An understanding of the soil environment's contribution to these outbreaks is essential to any comprehensive stem canker research program. This study was designed to assess the relationship between several soil properties and different disease levels occurring over a range of soil conditions. Experimental plots were established at six sites that differed in depth of past erosion. A high-fertility status (P, 140 kg ha^-1; K, 280 kg ha^-1) was maintained on one half of the plots at each site. The remaining plots were left unamended. Visual estimates of stem canker infection levels in 1986 equalled 72 and 86% for the fertilized and unfertilized treatments, respectively, at the slightly eroded site. Estimates for similar treatments at the most severely eroded site were 3 and 2%, respectively. Regression analysis indicated that soil organic matter content, pH, and soil water accounted for 66% of the variability in infection levels among the differentially eroded sites; whereas, plant residues from the previous crop year had no influence. Higher infection levels associated with the unfertilized plots were significantly correlated (P < 0.01) with lower concentrations of K in the soybean plants. These results indicate that greater stem canker infection levels can be expected on soils with higher organic matter, pH, and soil water content, and on soils that contain lower amounts of potassium.

Received for publication March 18, 1988.