Tomato diseases are rarely fatal, if the proper management is employed. It is important to catch any tomato disease early, before it spreads to all of your tomato plants and possibly other plants in the same family, such as potatoes, eggplants and peppers. Here are some common tomato diseases, their symptoms and what to do if tomato diseases threaten your home vegetable garden.
Tomato Diseases - Foliage
Early Blight Early Blight can affect the foliage, stems and fruit of tomatoes. Symptoms: Dark spots with concentric rings develop on older leaves first. The surrounding leaf area may turn yellow. Affected leaves may die prematurely, exposing the fruits to sun scald.
Management: Early Blight fungus overwinters in plant residue and is soil-borne. It can also come in on transplants. Remove affected plants and thoroughly clean fall garden debris. Wet weather and stressed plants increase likelihood of attack. Copper and/or sulfur sprays can prevent further development of the fungus. The biofungicide Serenade® lessens problems.
Gray Leaf Spot Gray Leaf Spot affects only the leaves of tomatoes, starting with the oldest leaves. Symptoms: Small, dark spots that can be seen on both the top and bottom surfaces of the leaves. The spots enlarge and turn a grayish brown. Eventually the centers of the spots crack and fall out. Surrounding leaf areas will turn yellow and the leaves will dry and drop. Fruit production is inhibited.
Management: Warm, moist conditions worsen gray leaf spot problems. Remove all affected plants and fall garden debris. Select resistant varieties. More info and photo from Texas Cooperative Extension
Late Blight Late blight affects both the leaves and fruit of tomatoes. Late Blight is the disease responsible for the Irish Potato Famine. Late Blight spreads rapidly. Cool, wet weather encourages the development of the fungus. If you suspect you have Late Blight, contact your Local Extension Service for definite ID. Symptoms: Greasy looking, irregularly shaped gray spots appear on leaves. A ring of white mold can develop around the spots, especially in wet weather. The spots eventually turn dry and papery. Blackened areas may appear on the stems. The fruit also develop large, irregularly shaped, greasy gray spots.
Management: Copper sprays offer some control. Serenade® works best as a deterrent, rather than a cure.
The Late Blight fungus can overwinter in frost free areas. Since it spreads to potatoes, it also overwinters in potato debris and seed, even in colder areas. Remove all debris and don't save seed potatoes. More info and photo
Septoria Leaf Spot Septoria Leaf Spot is sometimes mistaken for Late Blight. With septoria leaf spot, the papery patches on the leaves develop tiny, dark specks inside them. Older leaves are affected first.
Management: Copper sprays and Serenade® are somewhat affective at halting the spread of symptoms. More info and photos
Southern Blight Southern Blight manifests as a white mold growing on the stem near the soil line. Dark, round spots will appear on the lower stem and both the outer and inner stem will become discolored. Southern Blight fungus girdles the tomato stem and prevents the plant from taking up water and nutrients. Young plants may collapse at the soil line.
Management: Crop rotation seems to help. There has also been some evidence that extra calcium and the use of fertilizers containing ammonium offer some protection. More info for control from Minnesota Extension Service and photos from Louisiana State University Ag Center.
Verticillium Wilt This name can be misleading, as sometimes the leaves will turn yellow, dry up and never appear to wilt. Verticillium wilt is caused by a soil-borne fungus and it can affect many different vegetables. The fungus can persist in the soil for many years, so crop rotation and selection of resistant varieties is crucial. Symptoms include: wilting during the hottest part of the day and recovering at night, yellowing and eventually browning between the leaf veins starting with the older, lower leaves and discoloration inside the stems. Verticillium Wilt inhibits the plants ability to take in water and nutrients and will eventually kill the plant. Verticillium wilt is more pronounced in cool weather. (Verticillium wilt can often be confused with Fusarium wilt.)
Management: Remove affected plants and choose resistant varieties. More info and photo from University of Minnesota Extension Service
Read more about tomato diseases that affect the fruit.