Tomatoes may be affected by various disease causing organisms. Some common diseases affecting tomatoes include early blight, Septoria leaf spot and late blight. Gardeners may notice spots on leaves, lesions on fruit and stems and overall plant decline. Each of these diseases causes specific symptoms, and positive identification is key so you know what organism you are dealing with. Online resources are available at Michigan State University’s Dr. Mary K. Hausbeck Lab website to help with proper disease identification.

What is the best defense against tomato diseases for home gardeners?

Prevention is the best line of defense. You don’t even want the disease in your garden. Making use of the following Smart Gardening practices will help reduce the chances your tomatoes will develop any of these diseases:

• Select disease-resistant varieties.
• Water only in the morning to avoid moisture being left on leaves.
• Do not work around plants when they are wet.
• Practice good sanitation, i.e., remove any dead or diseased tissue from the garden and destroy it.
• Rotate crops, i.e., don’t plant the same plant or plant family in the same location for at least every three years.

Selecting resistant varieties is an option if you find yourself struggling with tomato diseases. Check out seed catalogs for specific varieties that are resistant when planning next year’s garden. Some varieties have been developed that will resist a certain disease.

Smart gardeners choose to not water plants with overhead sprinklers, but use drip irrigation or water plants directly at their base. This practice allows the water to reach the roots where it will be most useful, and it keeps water off of the leaves. Having water on the leaves for any length of time is an invitation for these diseases. Fungal diseases like moist conditions, and the longer the leaves are wet, the better the chance a fungus has to move in and attack. The late blight organism actually has a stage in its life cycle that is able to swim, so it will really take advantage of water on the leaf surface to spread.

What should a smart gardener do if you see disease symptoms?

Proper identification of the disease type is important so you know what disease-causing organism you are dealing with. Use of fungicides is only good for preventing the disease. In other words, if you are already seeing disease symptoms, fungicides will not cure or fix the plant. They are only to be used before the onset of disease. There is a late blight risk monitoring state map across Michigan, so you could potentially treat with a recommended fungicide for prevention if the disease has been reported in your county.

If your plants are already showing disease symptoms, one way to delay the disease is to remove the infected leaves as soon as you see them and destroy them. Michigan State University Extension does not recommend you compost this material as it’s not guaranteed you will destroy the disease-causing organism. Always practicing good sanitation is critical for disease prevention as these organisms will overwinter in the infected plant material. Check out “Organic Management for Early Blight on Tomatoes” and “Organic Management for Late Blight on Tomatoes” from the Dr. Mary K. Hausbeck Lab website.

Be sure to call MSU’s toll-free garden hotline at 1-888-678-3464 if you need additional information or advice concerning tomato diseases. For more information on a wide variety of Smart Gardening topics, visit the Gardening in Michigan website at www.migarden.msu.edu.