Good Growing: Keeping tomatoes healthy
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Photo by University of Illinois Plant Clinic
Septoria leaf spot is a common disease of tomatoes that causes small circular spots on leaves.
Tomatoes are one of the most commonly grown vegetables in home gardens. While tomatoes are relatively easy to grow, there are a few diseases you should keep your eye out for. Three of the most common diseases people encounter are early blight, Septoria leaf spot, and anthracnose. All of these diseases are caused by fungi. Consistently wet conditions are required for these diseases to develop.
Early blight primarily infects the foliage of plants, but it can also infect the stem and fruit. It appears as irregularly shaped brown spots that have concentric rings (resembling a bull’s-eye or target), commonly on older leaves. The spots are often surrounded by yellow tissue. The spot can grow to be ¼ to ½ inch in diameter and will often grow together, forming large brown areas. Eventually, leaves will drop off plants.
Septoria leaf spot is also primarily a leaf infection, but it will also infect the stems. It forms small circular spots on leaves. These spots have a tan or light-colored center with dark purple or brown margins. Spots will grow to be around ¼ of an inch in diameter. Like early blight, the individual leaf spots will often coalesce, forming large areas of diseased tissue. Heavily infected leaves will turn yellow and fall off the plant. Unlike early blight, it does not form concentric rings. But, if you look closely, you can often see small black pimple-like fruiting bodies in the center of the leaf spots.
Anthracnose is primarily a fruit disease. Circular sunken lesions develop on fruit. Over time, these spots will enlarge and darken. Often, pink to orange masses of spores form in rings on the. Anthracnose may occasionally be found on leaves and stems, where it will cause irregularly shaped brown spots with dark brown edges.
Managing tomato diseases
There are a few things you can do to manage these diseases. First, remove and destroy any diseased foliage and fruit to help prevent disease from spreading further. When removing it, don’t just throw it on the ground; get it out of the garden! Make sure plants are dry before working with them; if leaves are wet, you may end up spreading the disease.
Early blight and anthracnose can survive in the soil, on seeds, or in infected plant debris. While Septoria can survive for up to three years on infected plant debris, as well as weedy hosts, it does not survive in the soil on its own. Using mulch around plants can help create a barrier between the soil and the plants. When watering plants, avoid watering late in the day and try not to get the foliage wet. The longer the leaves remain wet, the greater the chance that disease will develop.
Fungicides can also be applied to plants. This will not get rid of the disease on infected leaves, but will protect healthy leaves from infection. When using pesticides, make sure to read and follow all label directions. Contact your local extension office to get a list of recommended chemicals.
Good Growing Tip of the Week: Contrary to popular belief, blossom end rot is not caused by a pathogen or insects; it is actually a physiological disorder. The cause of blossom end rot is poorly understood. It has commonly been believed that it is caused by low levels of calcium in developing fruit or due to stress on the plant.
