Tomato-plant diseases are caused by bacteria, fungi, and viruses—and the diseases can spread through the soil, water, air, infected tools, animals, and even by gardeners themselves. Use these techniques to avoid tomato diseases in the first place:
Rotate crops regularly
Many bacteria, fungi, and viruses live in the soil for years and are just waiting to prey on your tomato plants! Minimize the likelihood of these diseases when you plant tomatoes no more than once every three years in the same location.
Avoid planting other crops such as potatoes, peppers, or eggplants nearby, too. As members of the same plant family as tomatoes, these crops are susceptible to the same types of diseases as tomatoes and having any of these plants nearby could facilitate more rapid spread of any developing disease.
Good old-fashioned crop rotation is good for your plants and good for the soil.
Improve your soil composition
Before planting your tomatoes, add a good amount of compost or organic matter to improve the soil. Extra nutrients and good aeration help grow stronger plants that will resist disease and infection.
Grow disease-resistant tomato varieties
Many hybrid tomato varieties have been developed specifically to resist particular tomato diseases. You can plant disease-resistant tomato varieties to ensure the healthiest plants and harvest. Tomato-disease-resistant codes are listed on seed packets or seedling containers in capital letters. They include:
- V = Verticillium Wilt
- F = Fusarium Wilt
- N = Nematodes
- A = Alternaria
- T = Tobacco Mosaic Virus
- St = Stemphylium (Gray Leaf Spot)
- TSWV = Tomato Spotted Wilt Virus
Water your garden properly
Don’t underwater or overwater your tomato plants. By keeping a regular watering schedule, you’ll keep your plants vibrant and healthy. Overwatering and watering directly on the plants—instead of the preferred watering method, directly at the base of the plant on the soil—leads to consistently wet conditions, which allows bacteria, fungi, and viruses to thrive and multiply. Never use a sprinkler system to water your tomatoes.
Destroy infected plants
Throw away or burn infected plants. Don’t keep infected plants over the winter in your garden, and don’t throw them on your compost pile either. Disease-ridden plants, even when dead, will spread the disease to other plants or even your soil.