To identify a tomato plant illness, you must examine the leaves, stems, roots and fruit of the plant. Different types of illnesses will affect different areas of the plant in the beginning, and most will spread throughout the plant if left unchecked. Fruits may seem healthy even when leaves start to discolor, but when left unchecked, the illness that is affecting the leaves may reduce harvest amounts and even limit overall growth.
Signs of plant illness include yellowed or spotted leaves, brown splotches on the stems and rotten spots on the fruit. Illnesses that usually first show on the fruit include blossom end rot, catfacing and sunscald. Initial leaf or bloom illnesses include early blight, leaf spot, leaf curl and blossom drop. Late blight is often seen first on plant stems.
Though some illnesses such as leaf curl cause little if any damage to the fruit, most other ailments will cause anything from tomato disfigurement and low yields to devastating crop failure. Dark spots on leaves will grow from small to encompass the entire leaf, often causing wilting and curling. Dark splotches on stems can mean virus or fungal infections, which may move from plant to plant. Cankers and mushy spots on the tomatoes are caused by pests, viruses, too much sun or nutritional deficiencies.
Most tomato illnesses can be remedied if identified and treated early. Performing daily garden maintenance ensures routine inspection, making it much easier to prevent the spread of pests or disease through healthy plants. Certain viral infections cannot be treated, so removal of the affected plant is the only action that can save the rest of the garden.
Healthy tomato plants are less susceptible to illness. To prevent illness, provide adequate space between plants, rotate crops, keep the garden free of weeds and debris. Test garden soil before every crop and use organic compost to improve the ground. Follow planting directions for each variety grown, and use disease-resistant varieties when able.
Some bacteria and fungus-caused illnesses will linger in the soil and cause damage to future crops, so tomatoes should be planted in a different area of the garden each year, and keep the plants from the site of infection for at least three years. If the plant is affected by an illness that can spread, remove it from the garden and throw it in the trash. Keep infected plants out of the compost pile, and treat the garden soil before planting the next crop. Illnesses that cause leaf damage might not spread to the rest of the plant, but they may still leave the tomato susceptible to sunscald and yellow shoulders. Whenever the leaves are affected by an illness that makes them drop, wilt or curl, shade the plant to limit the hours the tomatoes spend in direct sunlight.