Warm temperatures, in the 80°-90°F range, and wet weather favor infection. The disease first shows up as yellow flecks on the leaves, which later turn dark brown. Individual spots are usually irregular in shape and remain fairly small, surrounded by a narrow yellow margin, but lacking a wide yellow halo.
Plant disease-free seed, rotate crops, burn infected plant tissues and clean contaminated equipment. Avoid working with plants when they are wet, as water transmits the bacteria. To prevent infection, or reduce its spread, apply a copper soap fungicide at 7- to 10-day intervals. After heavy rain, or when the amount of disease is increasing rapidly, apply every 7 days or more frequently at the highest recommended rate. We recommend Soap-Shield Flowable Liquid Copper Fungicide.