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Bacterial Brown Spot Widespread on Dry Beans
Bacterial brown spot is common on dry beans in areas with abundant to excessive rainfall.
SYMPTOMS. Brown spot develops first on the leaves. The spots are circular, about 1/8 inch across and brown, often with a narrow yellow border. Later the spots may coalesce, producing large spreading or elongate brown areas, and tearing of the tissue. Dry, sunny weather will stop progress of the disease.
LOSSES. Measurable losses occurred in 1993 for the first time in North Dakota. Data from Wisconsin and Colorado indicate that some economic losses may occur, possibly as high as 20-30% in rare cases. Losses this high may have occurred in a few selected fields in North Dakota in 1993.
FUNGICIDES. The copper fungicides Kocide DF and Kocide 101 are registered for control of brown spot. Other Kocide and Champ/Champion fungicides are registered for dry beans, but not bacterial brown spot. Best results in Colorado and Wisconsin were from multiple (4-5) applications of copper beginning before bacterial populations were high. They were obtained by applying the first spray to the first trifoliate or as soon as disease was noted. This might not be economic in some years. Making one or two applications when disease is severe and bacterial populations are high may not provide much control, although it may slow down spread somewhat. The economics of this practice are questionable.
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