Septoria leaf spot appears as small round spots on the upper side of the leaf.… (FRAN KITTEK, SPECIAL TO…)
Q: I have addressed this problem with you several years ago but I still have it. I have talked to several garden centers and they all give me different answers.
You suggested buying wilt-resistant plants, which I have done but it hasn't helped. I have even moved my tomato garden to a different location. Is there something that I can do with my soil to try to avoid this problem next year? My plants are dying from the ground up. I have tons of fruit on the plants but I'm afraid the plant won't live long enough for the fruit to ripen. I'm at a loss yet again this year.
—Jane, Moore Township
Q: My tomato plants have black spots all over the leaves and stems and although I keep trimming them off, it persists. Also the large tomatoes refuse to turn red. I have picked a couple of large green tomatoes and am hoping they will ripen inside. Will they? And are these tomatoes OK for fried green tomatoes?
A: Jane sounds like she has Septoria leaf spot (Septoria) on her tomatoes. While she has taken some effective measures to protect her tomatoes there are a few more things she can do. Lisa may have the same problem as well.
But first, Septoria leaf spot is a common fungal problem for all solanaceous plants, tomatoes, eggplant and potatoes, to name the most common, the nightshade family.
Although it does not directly attack the tomato fruits, the leaf loss can result in sunscald or even a failure to ripen. The problem most often occurs as the plants grow dense and leafy.
This restricts the airflow around the plant and creates an environment favorable to fungus. High humidity and a few cool nights (68-77 degrees) added to the mix and you've got heaven for fungus. Small circular spots appear on the upper side of the leaf.
Septoria usually appears first at the base of the plant. Here, the humidity is the highest and the spores can easily splash up from the soil. The spots have dark edges and a grayish center. In the spot are small black or brownish spots: these are the fungal spores, ready to mature and spread to other plants. The leaves eventually die and the problem moves up the plant until the entire plant is killed.
So what should a gardener do? Jane did many of the recommended preventive measures:
•Resistance to Septoria: Although there are varieties with fungal resistance, I could not locate a variety that was specifically resistant to Septoria.
•Crop rotation: Move plants to a different locationin the garden each year, ideally not growing the same or related crop in the same spot for three to four years. It isn't good enough to move the tomatoes, if you plant a related crop, say eggplant, in the same spot.
But there is still more that can be done:
•Adequate air circulation: This refers not only to the space between plants but also the circulation of air within the plant. Ideally, allow about 24 inches between plants and consider thinning some of the foliage off the tomato plant when it becomes dense and leafy.
•Clean up: Remove and destroy infected foliage as it occurs. At the end of the season, remove infected plants and destroy. The spores winter-over in the dead plants and can readily infect the next year's plants.
•Maintenance: Avoid working among the plants when the leaves are wet. You can transfer spore to susceptible leaves in this environment.
•Water: Water early so the plants have time to dry off before the cooler evening temperatures occur. Try to water at the base, avoiding wetting the foliage.
•Staking: Stake plants. This improves the air circulation and lessens the chances of fungal problems.
•Mulch: Mulching not only conserves moisture and suppresses weeds, it also provides one more barrier between your plants and the fungal spores in the soil. Splashing is a very common method of infecting plants.
•Fungicides: Fungicides can be labor-intensive and expensive. Apply an approved fungicide when the first fruit clusters appear or at the first sign of a problem. Generally, the fungicide needs to be applied every 7 to 10 days when the weather is wet and warm — most of the rest of the growing season. Be sure that any product used is safe for vegetables and effective against Septoria leaf spot. Follow all safety precautions and directions.
Finally, to Lisa's question about eating the tomatoes, yes, they are fine for fried green tomatoes or one of my favorites, pickled tomatoes.
Sue Kittek is a freelance garden columnist, writer and lecturer. Send questions to Garden Keeper at firstname.lastname@example.org or mail: Garden Keeper, The Morning Call, P.O. Box 1260, Allentown, PA 18105.
This Week in the Garden
•Plant but protect from heat: late-season cabbage, carrots, cauliflower, peas, and broccoli for late summer or early fall harvest.
•Stop planting perennials, shrubs and trees. Gather unplanted pots together and water regularly. Hold off planting until cooler fall/late summer weather.