The Q&A Archives: Dark circles on tomatoes

Question: Last year my Sweet 100 and Celebrity tomato developed dark concentric circles. The leaves turned yellow and eventually the whole plant died. What is this disease and how do I control it? Robert Sadowsky Montvale, NJ

Answer: The concentric circles are a clear sign of early blight, says Steve Reiners, Extension horticulturist at Rutgers in New Brunswick, New Jersey. This fungus is widespread in gardens and thrives in rainy, wet weather such as we had last year, says Reiners. The spores are blown onto leaves causing the circles, and eventually, death. Your first line of defense is preventive measures. Stake or cage the plants so they are off the ground. Space them three to four feet apart to increase air circulation and reduce humidity. In the fall, reduce the overwintering spores by raking up the spent stalks or tilling them in. You can also spray to control the early blight before it occurs. Copper spray applied after every rain starting in July can prevent the disease, says Reiners.

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