Tomatoes are the most popular home gardening crop. The taste of a homegrown tomato is far superior to those pale competitors from the supermarket. Tomatoes are nutrient-rich, containing fiber, antioxidant vitamins A, C and E as well as B vitamins and minerals. Unfortunately, tomato plants are prone to leaf and fruit diseases that must be treated to maintain production.
Early blight is caused by a fungus. It presents initially on the lower leaves of a plant, causing brown or black spots. Affected leaves will turn yellow and die. The fungus may also attack the tomato fruit, leaving large, sunken areas at the stem attachment that are black and soft.
Fungicides, such as maneb, mancozeb, and chlorothalonil, are effective when applied at the first sign of early blight and continued every 7-10 days. A preferred strategy is to plant disease-resistant varieties, rotate crops, and keep plant leaves dry using ground-based rather than overhead watering, and sufficient spacing to allow air circulation.
Fusarium wilt attacks certain tomato cultivars that are not resistant, such as many heirloom tomato varieties. This soil-dwelling fungus attacks the plant from the bottom up and the lower leaves will discolor before bending down or wilting. Because fusarium wilt is an internal infection of the tomato's water-conducting tissue, fungicides are not an effective treatment. If your garden soil has residual fusarium wilt fungus, your best option is to plant disease-resistant cultivars and rotate crops on a four-year cycle.
Blossom End Rot
Blossom end rot is caused by a lack of calcium. However, the treatment does not involve simply adding calcium. Rather, this physiological disorder results from environmental stress that impact the plant's ability to use the calcium in the soil. The stress is caused by variable moisture often because of sustained high temperatures followed by rainfall or watering.
Tomatoes with blossom end rot will show sunken black or brown areas on the blossom end of the fruit. To treat blossom end rot, remove the affected fruit, mulch the plants to retain moisture, provide consistent watering, and limit the application of nitrogen-rich fertilizers.
Bacterial spot presents on tomato leaves as dark spots about 1/8 inch in diameter. As the spots develop, they have a yellow halo around the spot and several spots may merge into large, irregularly shaped areas of damage. On the tomato fruit, the spots are black and slightly raised. A fungicide may be used to treat this infection and a spray of fixed-copper product can reduce the spread to other plants.
Septoria Leaf Spot
Septoria leaf spot is another fungus caused tomato plant disease. It appears initially as a small, circular spot about 1/8 inch in diameter. The lesions develop a grayish white center that eventually has a black speck. The light-colored center of Septoria leaf spot disease differentiates it from bacterial spot. Fungicides are effective in controlling septoria leaf spot if applied as soon as the disease is detected.