Tomatoes are susceptible to numerous fungal diseases such as early blight, septoria leaf spot, anthracnose, fusarium wilt and late blight. Septoria leaf spot is one of the most common fungal infections in tomatoes, and can occur at any stage of growth. Early and late blight thrive in damp, rainy conditions. Anthracnose can survive frigid winter temperatures and attacks mainly the fruit. Fusarium wilt dwells in the soil and occurs mainly in the warmer months. These diseases are difficult to eliminate once the plant becomes infected, and can decimate the crop over the course of the growing season.
Rotate crops to ensure that tomato plants are only planted in the same location once every three years. If using containers, discard used soil and wash them thoroughly before replanting.
Remove all debris and dead plants from previous crops before setting new plants in the soil. Burn old plant debris to destroy any lingering diseases. Continue to remove any dead or discolored leaves as the plants grow.
Keep your tomato plants upright and off the ground by supporting them with tomato cages or by loosely tying your plants to stakes using heavy string, cloth strips or pantyhose legs.
Apply a 1 to 2 inch layer of mulch around the base of each tomato plant, during planting, to control moisture and temperature levels, and to prevent soil from contacting the stem and branches of the tomato plant. Replace mulch, as needed, when it gets washed away by watering or rain.
Water tomato plants at the base, rather than spraying the entire plant. Moisture that lingers on the leaves can leave the plant vulnerable to fungal attacks.
Apply a fungicide, according to manufacturer's directions, shortly after planting and then at least every 10 days throughout the growing season. Be sure to apply fungicides after rain has fallen so that the product is not washed away.