Impact of drainage and at-plant fungicides on Rhizoctonia Root Rot in navy bean

Rhizoctonia root rot of navy beans (Phaseolus vulgaris) caused by Rhizoctonia solani can cause significant yield loss in poorly drained soils. Effective seed treatments against Rhizoctonia are available but are only effective for a few weeks after planting. However, the interaction between field drainage and fungicides remains unclear. Understanding these effects is critical for optimizing disease management. We evaluated the impact of drain-tile spacing and at-plant fungicides on navy bean plant stands and yield. A four-year field trial was conducted with five drainage treatments (0, 4.6-, 7.6-, 12.2-, and 18.3-m tile spacings). A randomized strip-plot design with four replications and navy bean cultivar T9905 was used. R. solani (AG 2-2 IIIB & IV) inoculum was worked into the soil prior to planting. Fungicide treatments included a nontreated control (NTC), sedaxane seed treatment (ST), and in-furrow (IF) azoxystrobin application. No significant interactions were found between drain spacing and fungicide application for any response variables. Drain spacing did not significantly impact plant population or yield. However, fungicide treatments significantly influenced stand and yield. The NTC had the lowest plant population, while the IF application resulted in the highest yield. These findings indicate that while drainage does not significantly affect navy bean plant populations or yield, at-plant fungicides play a crucial role in improving stands and overall disease reduction. The IF application has potential for optimizing Rhizoctonia control in poorly drained soils.