My tomato plants are sick or the fruit is disfigured (or both). Help!
There are so many potential tomato problems it’s a wonder we ever ripen a red fruit…but we do. Here’s the barest minimum of explanation to why some tomato problems occur, followed by links to expert diagnostic sites that may help you get even more specific.
Rot on the bottom: The bottom of a tomato fruit is the blossom end, where the blossom used to be before the fruit expanded. Blossom-end rot can appear as leathery and sunken, or be watery-looking; the end is discolored, and dark. I had it on my first fruits in 2010, and here’s what I learned then. The cause: not enough calcium, caused by water stress. Some gardeners work lime or calcium into the beds as a preventive measure, but does it help?
Green on the top: On the top or stem end, problems such as “greenback” can occur when areas around the stem remain hard and green, unripened. Too much sunshine can sometimes be the culprit there.
Seeing spots? Various fungal diseases, cankers, viruses and bacterial conditions can show up as spots on tomato skin, whether red or green. If your tomatoes get anthracnose (sunken round spots that then go dark in the middle, sort of a bull’s-eye effect), alternaria canker (also known as blight, with numerous sunken gray-brown marks on fruit, both green and red, and lesions on plants, too), or black mold and ghost spot (watery spots with dark centers), crop rotation might have helped prevent it, and is a must next year.
A three-year cycle is ideal; two is good; skipping a year helps with some conditions and not others, but is better then no rotation.
A barrier of clean mulch applied at planting time can reduce some spores that splash up from the soil onto plants. Heirloom tomato expert Amy Goldman is using a new (reusable) material, ground cloth, the stuff of greenhouse floors and nursery pathways.
Tomato foliage can also experience all manner of spotting, and many such afflictions are symptoms of the same cankers, blights, fungi and viruses above. Sometimes leaves start to fall off after yellowing, moving up the plant, other times it’s top-down. Bacterial wilt is a top-down deal; fusarium and verticillium begin at the bottom of the plant.
Cracks in the fruit often develop when soil moisture is uneven, and lots of moisture becomes available suddenly after not enough. Fruit swells faster than the skin can expand. Too much Nitrogen can bring on cracking, as can some fungal diseases and even merely plant genetics (large-fruited beefsteak types are said to be more susceptible).
Other damage to fruit can come from hail, from sucking insects, maybe from fire and brimstone, huh? It really is endless. So much so that there’s a whole annual conference called the Tomato Disease Workshop for breeders, farmers, and other professionals to try to work on problems together, and even an international version that in 2010 took place in Italy. Think pomodoro!
My favorite diagnostic sites: The University of Maryland, as well as Texas A&M and also Cornell University, each has a great, photo-driven diagnostic tool that you will want to bookmark. Rutgers has a great PDF on fungal diseases of tomatoes. And Cornell’schart of the disease resistance of various tomatoes was one of the most extensive I could find.