Dark brown spots on your tomatoes? It’s probably early blight.
Cool spring temperatures and too much rain or other moisture creates the perfect storm for this fungal disease. The early blight fungus (Alternaria solani) is a disease of the nightshade family, which means your potatoes, eggplants, bell peppers, and chili peppers are equally susceptible, as are other plants in the nightshade family, such as petunias and blue potato bushes. If similar lesions are seen later in the season, it is more likely to be late blight, also known as the dreaded potato blight.
Early blight was once a disease found only on the east side of the Rocky Mountains. Sadly, that is no longer the case. The early blight pathogen is now found everywhere host plants have been grown and can result in up to 30% of your potatoes and 79% of your tomato crop ending up in the trash bin.
Early blight symptoms
Small black or brown spots, usually 1/4 to 1/2 inch in diameter, may appear on fruit, leaves, and stems. These spots may have a concentric rings pattern, or bullseye. Fruit spots are dry, sunken areas, most commonly seen near the calyx end of the fruit. [That’s the flower end, as opposed to the stem end.] Spots on leaves feel leathery. Symptoms are seen on older leaves first. Stem lesions do not have the same circular, bullseye pattern.
In some cases, this pathogen can cause collar rot and damping off, which usually kills seedlings. As the disease progresses, leaf loss can significantly reduce fruit production. Honestly, the fruit that is produced doesn’t look particularly appetizing. Infected potatoes either rot in the ground or in storage.
Early blight lifecycle
Fungal spores overwinter in the soil and on infected fruit and plant debris. Rain and overhead irrigation splash spores onto plants, where they begin reproducing. To reduce the chance of early blight in your garden:
Fixed copper or sulfur sprays can provide fungicidal benefits in heavy infestations. Also, healthy plants are less likely to become infected, so feed and water your plants properly, give them enough space to reach full size, and help them avoid physical injuries, which provide entry points for early blight fungal spores.
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