After all the work you put into growing them, few things are as frustrating as finding brown spots on your home grown tomatoes. Brown spots are typically caused by fungus or nutritional deficiencies. Keep a close eye on your tomato plants and change your cultural practices to reduce brown spots on your tomatoes.
Soil rot is caused by a fungus in the soil called Rhizoctonia solani. It shows up on parts of the fruit that touch the ground or where soil splashes onto the fruit during rain or watering. Spots are large and sunken in, sometimes with a target pattern. The best way to prevent this type of rot is to keep the fruits from touching the ground. Do this by staking up the plant or by mulching around it. Mulch helps keep the soil moist while preventing it from splashing up onto the plant. Watering using a drip irrigation system may also help.
Blossom End Rot
Blossom end rot starts out looking like a water-soaked spot on the fruit, forming on the blossom end, as the name suggests. This eventually turns into a dark, leathery, sunken area. Blossom end rot is caused by a calcium deficiency from inconsistent watering, root pruning or too much nitrogen in the soil. To prevent this problem, use a fertilizer high in phosphorus and avoid anything that might damage the roots. Apply mulch around your tomato plants to keep the soil moist and water regularly to keep the soil moisture consistent.
Early blight is recognized by dark spots near the stem that appear leathery and sunken. The fruits actually become infected with the Alternaria solani fungus when they are still green. Damp, rainy weather early in the growing season contributes to infection. Watch the tomato plant for signs of leaf blight, the yellowing and withering of leaves, which is the first indication of early blight. Fungicidal sprays can control early blight, as can crop rotation because growing a crop in the same place each year depletes the soil, leading to nutritional deficiencies and disease. Staking plants and mulching the ground around them will help control this disease as well.
Anthracnose is a fungal infection that shows up as sunken, circular area that becomes dark in the center. As with other fungal infections, soil splashing up on fruits during watering causes the fungus to spread and take hold. Crop rotation, fungicidal sprays, mulch and staking of plants will help minimize the occurrence of anthracnose.
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