It's a tough year for tomatoes -- or any plants that are heat-loving or particularly vulnerable to fungus diseases. At Cornell Cooperative Extension, where Master Gardener volunteers answer gardening questions, recent calls and samples indicate many such tomato troubles.
Many people want a pat solution to failing, drooping, wilting, yellowing tomatoes, but there is no quick fix. To help you, we must ask some questions to arrive at a diagnosis, and then pass on what Cornell recommends to do about it.
Here are some possible signs and symptoms of diseases:
Yellowing, dropping older leaves -- Verticillium wilt: Older leaves yellow and dry up. Later leaf tips curl inward. This fungal disease thrives in cool, humid seasons -- and we are seeing it. Management approaches include crop rotation, next time choosing resistant strains labeled "V," fall cleanup and sulfur fungicides applied as labeled.
(Another wilt disease, Fusarium wilt, also starts with yellowing, and there is no effective treatment; the plant dies. Resistant varieties are labeled "F.")
Dark spots on older leaves -- Early blight: Leaf spots show up early, which this year could be now, mature leaves first. Spots are ringed with a bull's-eye pattern. This remains in soil, so you must rotate next year and remove infested soil in raised beds or containers. Encourage air circulation by generous spacing and elevating the plants with cages or staking. Do not move among wet plants; it spreads it. There are fungicides labeled for early blight, but many gardeners keep removing infested leaves and still get tomatoes.
Dark "greasy" lesions -- Late blight: When you hear of greasy or water-soaked spots on leaves and later on fruits, suspect this serious disease. This is the one that caused the Irish potato famine (potatoes and tomatoes are in the same botanical family.) New York State growers have been threatened by it in recent years, so if you get this diagnosis you must destroy the plants. It requires a precise wet weather and temperature pattern to thrive, but once the spores are produced they live on in parts of the plants -- the debris left in the garden or cull-piles (throw-away piles).
That is why we teach: Don't let the "freebies or volunteer" potatoes or tomatoes grow next season, as those spores could severely damage commercial fields many miles away. Fungicides are not very effective.
Cultural, disease or insect?
Many more problems can beset tomatoes: slugs, sun scald, rotting, cracking and blossom-end rot (blackened bottoms) from irregular water when they are young. Don't just spray; get a diagnosis. Most plant problems are about soil and weather.
Why even try? Most tomato plants do not become diseased. Your best insurance policy always includes using great soil with lots of compost, allowing air circulation (staking in a wet season like this), discarding unhealthy plant parts, choosing resistant varieties and crop rotation. Tending the garden with a watchful eye usually wins.
Sally Cunningham is an educator in Consumer/Community Horticulture with Cornell Cooperative Extension of Erie County, and gardening book author.