Tomato Plant Diseases

Tomatoes are hardy and easy-to-grow, but they are susceptible to a variety of tomato plant diseases that can harm or destroy your plants. Recognizing and identifying the symptoms and signs of the disease is the best way to prevent damage or death to the plant. Once you have diagnosed the problem, you may be able to treat or control the disorder that is affecting your tomato plants. 

1. Early Blight.  Black or brown spots that form a target shape on the older leaves of your tomato plant are an indication that your tomato plant is suffering from early blight. This disease is caused by the fungus Altermaria solani and usually appears during the hotter months of the growing season. Along with the dark spots, the leaves of your plant may turn yellow and fall off. Early blight also affects the stems and the fruit of the plant. Remove the diseased leaves to keep early blight from spreading. You may use sulfur dust to keep newer leaves from becoming infected. You can prevent early blight by spacing your plants further apart to allow for proper air circulation and avoid watering plants from above as the water resting on the leaves can lead to early blight.
2.  Bacterial Canker.  Tomato plants infected with bacterial canker often have dark or light brown streaks on their leaves and may have cankers on their stems. The first signs of bacterial canker normally appear on the lower leaves of the plant which begin to turn and curl downward. Normally, only one side of the tomato plant appears to be infected at first ,but the disease eventually spreads to the whole plant. You may notice your tomatoes also show signs of the infection, which appear as raised, bumpy, white halo-like spots on the tomato. Copper based sprays can help reduce the spread of bacterial canker if they are used immediately upon discovering the disease, but you may end up having to destroy the plant to stop the spread of this tomato plant disease among the rest of your crops.
3. Septoria Leaf Spot. The most common foliar disease of the tomato plant is Septoria leaf spot. It is caused by the fungus Septoria Lycopersici and often occurs during long periods of rainy, warm, humid weather. The lower leaves of the tomato plant are affected  first and begin to show signs of the disease by developing gray spots with white centers.  As the infection spreads upward, the leaves will eventually turn yellow and drop. The best way to prevent Septoria leaf spot is to water plants in the morning around their base; avoid getting the leaves wet if possible. If your tomato plants appear to have Septoria leaf spot, treat them with a fungicide. Always follow the manufacturers instructions when using any chemicals. 
4. Fusarium Wilt. Brought on by a fungus that lives in the soil, Fusarium wilt causes the leaves of the tomato plant to yellow and droop and fall off prematurely. At first, only one side of the plant is affected, but eventually, the disease spreads to the whole plant. Chemical treatments or fungicides don’t help control Fusarium wilt. Since only certain tomato plants are susceptible to Fusarium wilt, you can avoid the disease by buying plants that are resistant to Fusarium wilt. Plants that are safe from the disease will have an “F” following the cultivars name. Resistant varieties can still become infected, but the disease will not be severe and they will still produce a delicious crop of tomatoes. 
5. Powdery Mildew. Caused by humid conditions and poor air circulation, powdery mildew is commonly found on tomato plants grown in greenhouses. White splotches, which eventually darken into brown lesions, develop on the top part of the tomato plants leaves and can lead to defoliation. Fungicides will effectively treat the disease if it’s caught quickly.