Tomatoes are found growing in most home gardens. The tomato comes in a wide variety of shapes and sizes and is served in a multitude of ways. Tomato plants are easy to grow, adapt well to most soil conditions and are a high-yield crop. Generally, tomato plants have few problems, but they are susceptible to several diseases that can take their toll on the leaves of the plant.
Caused by the fungus Alternaria solani, the first signs of early blight initially appear on the mature, lower leaves of the tomato plant. Large brown or black oddly shaped spots often take on a target-like appearance. The areas around the spot begin to yellow and leaves eventually drop. Early blight spreads rapidly to the higher leaves of the plant, which leads to defoliation. Other parts of the tomato plant may be affected by early blight.
Caused by Corynebacterium michiganense pv. michiganense, bacterial canker first appears on the lower leaves of the tomato plant. The leaves begin to wilt and turn brown, dry up and die. The tissue of the leaf becomes brown or yellowish-brown, and a yellow slim-like substance oozes from the affected leaf stem. Bacterial canker will eventually progress upward and affect all of the plant leaves.
There are two types of mosaic virus: tobacco and cucumber. Early signs of cucumber mosaic virus are yellow, stunted bush-like plants. Leaves will take on an elongated, narrow form and may have a severe fern-like or shoestring like appearance. Tomato plants infected with tobacco mosaic virus suffer from stunted growth. Light green and dark green spots spread over the leaves of the tomato plant. Leaves may turn downward and have a fern-like appearance.
The first signs of spotted wilt in a tomato plant are orange or bronze flecks that appear on younger leaves. The spots may take on a target-like appearance similar to the look found in early blight. The older leaves of the plant droop, turn brown and die. Spotted wilt will spread to the younger shoots, causing die back, and may appear as yellow spots on green tomatoes. Early spotted wilt infection will cause the death of the plant; later infections cause problems for the developing tomatoes.
Light green patches on the surface of older leaves is a sign that your tomato plant has leaf mold. The undersides of the leaf will develop patches of purple or olive green mold growth. Infected leaves eventually yellow and drop from the plant. The fruit and the stem of the tomato plant may be affected by leaf mold.
The fungus Phytophthora infestans causes late blight. Dark green or black spots start at the leaf edge and begin to spread inward. Misshapen spots have a slimy or greasy, wet appearance. During damp weather a downy, white growth develops on lower surfaces of the leaves near the outer edges of the spot. Spots will eventually develop on the tomatoes. The disease progresses rapidly when weather conditions are favorable.