As we finish out July and head into August, gardeners are looking forward to harvesting their tomatoes. Tasting that first, freshly picked tomato is a joy every tomato grower knows. But this is also the time to keep a look out for some common disease and disorders that may show up on tomato plants.
One common disorder is blossom end rot. Blossom end rot is characterized by a sunken, dark area at the blossom end of the tomato. It often occurs on developing fruit during times of hot, dry weather. It tends to have the greatest impact on the earliest-maturing fruit. Blossom end rot results from the plant being unable to provide enough calcium to the fruit as its growing. Calcium can become deficient when there is a wide fluctuation in soil moisture. Although blossom end rot means that the plant does not have enough calcium within the developing fruit, it does not mean, necessarily, that there is a lack of calcium in the soil.
The best way to prevent blossom end rot is to avoid irregular watering. Consistent, uniform watering will help keep a steady flow of calcium from the soil to the fruit. Apply mulch to retain soil moisture between watering and avoid large applications of nitrogen fertilizer. As mentioned, it’s the first fruit formed that is usually affected, fruit that develops later in the season on the same plant can be fine. For more information on blossom end rot, see the UW Madison Plant Disease Diagnostics Clinic (PDDC) fact sheet Blossom End Rot.
Another disorder I have seen lately is leaf roll. This involves the leaf edges rolling upward until they touch or overlap with each other. Common in hot, dry weather, it is also thought to be caused by fluctuations in soil moisture but can occur due to other stresses. Leaf roll is not known to reduce growth or fruit quality. Once leaves roll they may not unroll. Not all tomato varieties are equally susceptible to leaf roll so it may show up on some plants and not others.
While keeping an eye out for blossom end rot, I detected some leaf spots on a few tomato plants. My tomatoes have had this before – Septoria leaf spot. This fungal infection is one of the most common foliar diseases seen on tomatoes. It shows up as small, circular spots that have light-colored centers with dark edges. Symptoms first appear on the lower, older leaves then move up the plant. The spores of the fungus spread to new leaves by the splashing of water. Infected leaves can eventually turn yellow, shrivel and fall off.
Good cultural practices can help slow the progress of Septoria leaf spot. Remove affected leaves and dispose of any diseased debris on the ground around the plant. Watering at the base of the plant to avoid wetting leaves and applying about one inch of mulch can also help reduce the spread of the fungus. To learn more about Septoria leaf spot, see the UW Madison PDDC fact sheet Septoria Leaf Spot.
Another common fungal disease of tomato plants is early blight. This disease also causes leaf spots and often shows up this time of year. As with Septoria, early blight will first affect the lower leaves. Brownish, black spots form on the leaves and stems and will often run together creating larger, irregular shaped blotches. The leaf spots can also develop dark, concentric rings giving it a “target” appearance. The fruit may develop sunken areas near the stem end that take on a black, velvet-like look. Cultural controls for early blight are similar to those for Septoria leaf spot. To learn more about early blight, see the UW Madison PDDC fact sheet Early Blight.
Good observation is the first step when it comes to managing potential problems in the garden. Also, follow good cultural practices to help avoid or reduce garden issues:
• Water at the base of plants
• Do not overcrowd plants
• Weed
• Mulch
• Avoid injury to plants
• Remove & dispose of infected plant material
• Inspect for egg clusters, beetles, caterpillars, & other insects
• Rotate crops
• Keep a garden journal
