Tomato plant diseases are spread by wind, rain and infected soil. They can also spread from one plant to another by hands and tools. Most bacterial diseases that harm tomato plants live in the soil for three-four years or longer. That is why crop rotation is important for preventing tomato diseases in the garden. Tomato disease problems can be avoided with proper growing and sanitation techniques.
Septoria Leaf Spot
Septoria Leaf Spot is caused from water splashing on the leaves of the plant. It appears as gray spots with brown edges and small black dots in the gray middle area. It eventually covers the leaves of the plants and causes the leaves to turn yellow and fall off. When the leaves fall off, they cannot protect the fruit from the sun and sun scald of the fruit often occurs making the fruit inedible. Fungicides that treat Septoria Leaf Spot are not always effective and are difficult to find. The best control is to practice good garden sanitation by removing weeds and all old garden debris. It can live in the soil for three to four years.
The tobacco mosaic virus attacks not only tomato plants, but other vegetables and flowering plants. It is spread by the use of tobacco products around plants. It can also be spread by gardening tools and gloves. The leaves of the infected plant turn downward and become stringy and tough. The infected fruit is often mottled, deformed and stunted, which lowers tomato production. Plants infected with the tobacco mosaic virus should be removed from the garden as soon as possible. They will not grow out of the problem. It is usually brought into the garden from an outside source, so sanitation is important.
Tomato anthracnose is a serious disease of tomato plants caused by the fungus Colletotrichum coccodes. It lives in the soil on rotting pieces of old tomato plants. When new tomato plants are planted in the same location, rain and overhead watering causes the spores of the fungus to splash on leaves an fruit. The lower leaves are usually infected first, then it spreads to the rest of the plant and fruit. Control is accomplished by using tomato crop rotations on a three to four year schedule. Infected plants should be removed from the garden.
Early blight is the most common disease of tomatoes and is caused by the fungus Alternaria solani. It affects new plants and plants that are stressed from drought or over watering. The spores live in the soil over the winter on plant debris from the previous season. The disease appears on the lower leaves of an infected plant first as circles with dark centers. The leaves turn yellow and fall off exposing the fruit to sun scald. However, the disease usually kills the plant before any fruit can be produced. Good sanitation and removal of plant debris from the previous season is the best method of control along with crop rotation. Immediate removal of infected plants is important because the spores infect the plant within hours after exposure. Early blight can live in the soil for three to four years. That is why all tomato crop rotation recommendations use three to four years as the amount of time needed to eliminate common tomato diseases that live in the soil and affect the entire plants instead of just the fruit.