Tomato Diseases and Disorders
Norm Mofjeld, Anoka County Extension Master Gardener
Tomatoes are a popular homegrown vegetable, and there is no comparison in the taste of a store-bought tomato to one grown in your garden! Tomato plants require full sun and a long, frost-free season, and they are susceptible to several diseases and disorders; however, there are steps you can take to keep them healthy. Here are some of the most common issues and what you can do to prevent them.
Leaf spot diseases include early blight and septoria leaf spot. These fungal diseases cause brown spots on lower leaves when the plants begin to set fruit. The brown spots from early blight develop concentric rings, while those from septoria leaf spot expand to have tan centers. High humidity and water splashing onto leaves can spread these diseases upward. Early blight can also infect the fruit, which then develop leathery, dark spots and fall off the plant.
To manage these diseases:
• Check the leaves frequently for signs of the diseases
• Keep the leaves off the ground and stake the plant
• Water at the base of the plant and keep water off the leaves
• Pinch off any leaves with spots
Blossom-end rot affects the tomato fruit, causing it to develop a tan to black spot at the blossom end. It is caused by a calcium deficiency in the plant, and it can occur even if there is sufficient calcium in the soil. Calcium uptake can be affected by fluctuations in soil moisture, injury to roots, heavy applications of nitrogen fertilizer, hot weather, and other environmental conditions.
To control this disease:
• Water regularly
• Mulch the soil around plants to retain moisture between watering
• Avoid digging close to plant roots
• Remove diseased fruit
Sunscald is caused when the tomato fruit receives too much sunlight. It can occur when leaf spot disease or insect feeding cause plants to lose some leaves, exposing the fruit to more intense sun. A pale yellow to white spot appears on the side of the fruit facing the sun, and it can invite decay-causing bacteria and fungi. To prevent sunscald, avoid pruning too much foliage around the fruit.
Catfacing causes brown scarring of the fruit, particularly at the blossom end. The scars can extend into the flesh. Although the reasons for this disorder are not definitely known, possible causes include cold temperatures, disturbance to the flower buds and flowers, or contact with hormone-type herbicide sprays.
Yellow shoulders is a disorder where the top of the fruit (“shoulder”) never ripens and stays hard and yellow or green even when the rest of the fruit turns red. The inside of the tomato may also have a white, hard flesh. If this occurs, take a soil test to ensure that the tomatoes are getting adequate nutrition, or choose a different variety next year.
Recognizing problems and knowing how to manage them will make you a more successful tomato grower! For more information, visit: Tomato disorders | UMN Extension
Interested in becoming an Extension Master Gardener volunteer? Applications accepted now through October 1.
Visit https://extension.umn.edu/master-gardener/become-master-gardener to apply.