Effect of foliar fungicide application timing on the control of bean anthracnose in the navy bean ‘Navigator’

Bean anthracnose, caused by Colletotrichum lindemuthianum, can severely reduce bean yield and seed quality. A 2-year field study at two sites in southern Manitoba examined the effect of the timing of foliar applications of the fungicide pyraclostrobin (Headline® 250 EC) on the control of bean anthracnose in navy bean (Phaseolus vulgaris) ‘Navigator’. Single and (or) sequential applications of pyraclostrobin at a rate of 0.1 kg active ingredient (a.i.)/ha were made at four growth stages. Single applications of pyraclostrobin, at either 3 to 5 trifoliolate leave stage, early flowering (40% bloom), late flowering (80% bloom), or 10 days after flowering, reduced disease development in the crop canopy, but had inconsistent effects on pod infection, seed discoloration, and yield. Sequential applications of pyraclostrobin at the early and late flowering stages usually resulted in the lowest disease severity on all parts of the plant and in the highest yield. Sequential applications of pyraclostrobin at the late flowering stage and 10 days after flowering were less effective in reducing anthracnose severity and seed discoloration than the earlier sequentialapplication treatment. Both sequential-application treatments of pyraclostrobin had similar yields. Under Manitoba growing conditions, seed-borne infection by C. lindemuthianum resulted in yield reductions that ranged from 15.2% to 32.1% in the untreated bean plots.