If you are raising tomato plants in your garden, you should learn the signs and symptoms of tomato plant diseases. Examining parts of the plant and being alert to symptoms can help you identify your tomato plant's problems so that you can keep your plants healthy through and beyond harvest time.
Tomato plant diseases attack part or all of the plant. In most cases, they spread over time if they are left unchecked via fungal spores or bacterial invasion of the plant's vascular system. Even if a tomato plant disease is not actually fatal to the plant on its own, it can lead to a weakening in the plant's defenses that leads to another, more problematic infection, or it can cause your crop yields to decline.
The leaves of your tomato plant will provide a good clue about what type of disease your tomato plant has. If they are mottled with yellow and dark green areas, then your tomato plant likely has a case of tomato mosaic virus. On the other hand, yellow, purple or brown spots can indicate anthracnose, while black spots with empty, necrotic (dead) tissue and even holes in the middle usually indicate a case of shot-hole disease.
If your tomato plant is looking distorted, stunted or as if it has dead stems, then you may have a fungal infection called a gall infection. Galls are swollen, woody knots on the stem that can actually girdle a plant and kill parts of it entirely. They may turn the wood of the stem black or cause it to grow in a distorted fashion. Another issue that impacts the stems of tomato plants is bacterial wilt. If your stems are brittle and hollow or brown and mushy when they are cut open, your plant likely has a bacterial infection that is destroying its vascular system and making it difficult for the plant to shuttle water and nutrients to various parts of the tomato plant.
If you are noticing problems with the fruits of your tomato plant, then your crop may be irrevocably affected this season. However, you can save your plant and your crops next season. Tomatoes with sunken, brown lesions often indicate a case of anthracnose, while firm, greasy brown spots on the tomatoes can indicate late tomato blight. Cankers, which are a problem on the stems of tomatoes, can also spread to the fruit, creating hard, inedible areas on the tomatoes themselves.
Overall Plant Problems
In many cases, symptoms that start on one part of the plant can spread to another part if you don't fix the problem. For example, anthracnose might start out on leaves, but it will spread to fruit if you do not eradicate the problem before your tomato fruits start to mature. However, there are some diseases that impact the plant as a whole from the very beginning. Root rot, while sourced in the roots of the plant, causes the entire plant to wilt even in the presence of plenty of water. Molds and mildews--powdery mildew in particular--will overgrow an entire plant, covering it with a layer of infection that is black, white or gray and may be powdery or slimy. Fusarium, another fungal root rot, starts with the crown of the plant--the part just above ground--but swiftly impacts the entire plant, making it wilt, so that you may believe that the entire plant has been impacted at once.