(Backyard Gardener - Photo Illustration - MetroCreativeConnection)

Hello, Mid-Ohio Valley farmers and gardeners! Humidity and rain seem to be the theme this week in the valley. I have seen some corn starting to tassel and it won’t be long till many home gardeners are picking tomatoes.

Due to the wet weather, many tomato growers may notice a disease which starts as numerous tiny spots on lower leaves that enlarge over time. As they do, the leaf turns yellow and eventually dies. This is due to a common tomato disease called Septoria leaf spot, caused by the fungus Septoria lycopersici.

Frequent rain, high humidity and dew on tomato leaves lead to rapid disease development. Symptoms start on the lower leaves and then move upward. Septoria leaf spots appear as numerous brown spots approximately 1/16 to 1/8 inch in diameter on the leaves with gray or tan centers and dark brown margins. As the spots mature, dark brown pimple-like structures called pycnidia, which are the fruiting bodies of the fungus, appear inside the spots. These pycnidia can easily be seen with a hand lens.

Septoria leaf spots generally do not affect stems or fruit, but under high disease pressure spots may also appear on stems, calyxes and blossoms. Very rarely do they appear on fruit. Leaf loss due to severe disease may expose fruits to sunscald.

Although the fungus is not a soil inhabitant, it can persist from one season to the next on debris of diseased plants. Tomato seed has been shown to carry spores and produce infected seedlings, but it’s unknown if the pathogen is truly seedborne. The pathogen can also overwinter on solanaceous weeds such as horsenettle, black nightshade, jimsonweed and groundcherry.

Septoria leaf spot may be confused with early blight, which is caused by the fungus Alternaria solani. Early blight is characterized by a few (about 5 to 10) brown, circular spots up to half an inch diameter with concentric rings or ridges that form a target-like pattern surrounded by a yellow halo. As the disease progresses, stem and fruit also become infected forming dark, sunken spots. Dark, sunken cankers with concentric rings may also appear at or above the soil line on stems in case of an Alternaria infection.

There are several management techniques gardeners can use to prevent septoria leaf spot and other diseases in tomatoes. Staking or caging the plants to raise them off the ground should help in quick drying and preventing spores in the soil from splashing on tomato leaves. Make sure your plant spacing (24 inches) allows enough air movement and sunlight penetration for plants to dry out after a rain.

Using plastic or other mulch near the base of plants can also prevent splashing of soil particles that may contain fungal spores associated with debris. Water at the base of the plant with drip irrigation or a soaker hose instead of watering with a method that gets the foliage wet.

You can eliminate the initial source of infection by removing infected plant debris and weeds and use disease-free seeds. If complete removal of plant debris is not possible, destroy by deep plowing immediately after harvest. Do not plant crops in the Solanaceae family (tomatoes, peppers, potatoes, eggplant) for one year.

It is also helpful to select a resistant variety. Tomato varieties with complete resistance to Septoria leaf spot are not available. However, the variety Iron Lady shows tolerance to the disease and is now available. West Virginia 63′, Mountaineer Pride and Mountaineer Delight varieties with similar tolerance are also available and are the result of the tomato breeding program here at West Virginia University.

Remove lower infected leaves from the plant if detected early enough and bury or burn them immediately. Don’t add infected leaf or debris to the compost pile.

Fungicidal sprays may still be required in a rainy and humid season. Organic growers may use products containing fixed copper (Liquid Copperç, Copper Fungicideç) on a weekly schedule throughout the growing season.

Conventional growers may use products containing chlorothalonil (Daconilç, Bravoç), azoxystrobin (Quadrisç, Amistarç) or mancozeb ( Dithaneç, Manzate, ç).

If you have plant disease issues, consider utilizing the WVU Plant Diagnostic Clinic. They diagnose all kinds of plant problems for homeowners, gardeners, landscapers, growers and farmers. In 2018, more than 600 samples were diagnosed by the clinic. The submission form address of the diagnostic clinic and a video showing how to collect samples are located on the website extension.wvu.edu/lawn-gardening-pests/plant-disease/plant-diagnostic-clinic.

Before you submit a sample, contact me at the Extension office if you need help to properly collect and submit a sample to the WVU Plant Diagnostic Clinic. After the diagnosis, I can recommend control methods that are suitable to your location and situation with the assistance of our plant disease expert Dr. Mahsuz Rahman and our weed scientist, Dr. Rakesh Chandran.

Collect the whole diseased plant, plus healthy plant, if possible, including the roots. If a plant showing a systemic decline, the problem is likely originated from the root and root sample is a must. Collect more than one plant if they show various stages of decline. Do not collect a sample from a plant that has been dead for a while. For plant identification, collect the whole plant, if possible, including flowers and fruit.

Looking for more information? Contact me at the WVU Extension Office at 304-424-1960 or email me at jj.barrett@mail.wvu.edu with your gardening questions. Good Luck and Happy Gardening!