Tomato plants may experience a wide array of fungal diseases that can devastate the plant, kill your entire harvest or merely cause cosmetic damage. Many of these diseases display foliage symptoms that gardeners can identify. Proper planting of tomatoes will cut down on the likelihood of fungal diseases, but wet weather and poor care can exacerbate their occurrence.
Tomato plants can contract many types of fungi that bear symptoms on tomato leaves. According to Cornell University, they can get early blight, Septoria leaf spot, gray leaf spot, target spot, leaf mold, powdery mildew or late blight. Additionally, root rot diseases caused by fungus display some leaf symptoms.
Leaves affected by Septoria leaf spot display watery rings. The center of the ring turns gray and develops black spotting; the outer edge of the ring can turn brown or black. Leaves suffering from gray leaf spot wither and dry up. Their spotting is irregular; affected leaves can crack. Gray leaf spot occurs more in southern states. Another common virus in the south is target spot, which causes leaves to have circular lesions that grow into yellow halo-shaped lesions.
Mold or Mildew
Leaf mold occurs more often on greenhouse than field tomatoes, notes Cornell University. Affected plant leaves get yellow splotches on the top and brown spots on the bottom. Powdery mildew causes plant leaves to become coated in a fine white or gray powder. This occurs more in the western states.
Keep tomato plants healthy by providing adequate nutrients and optimal growing conditions. Colorado State University advises that gardeners properly space tomato plants in the garden to promote light and air circulation. Water tomato plants whenever the soil becomes dry to avoid causing stress; provide plant nutrition either via fertilizer or by mixing manure or compost into the soil before planting. Only plant disease-resistant tomato plants that you've purchased from a local nursery, farm or garden center.
Avoid getting tomato plant leaves wet, since wet leaves are more prone to fungal infection. Rotate annual planting of tomatoes so the soil does not harbor bacteria or fungi.
Gardeners can apply fungicides to treat tomato leaf fungus after they've identified the type of fungus. Using the wrong fungicide may not treat the problem. To determine how to treat your plants for fungal diseases, contact your county extension office and ask for a list of fungicides approved for use in your area.