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Getting ripe, healthy tomatoes presents some problems. Be sure to do whatever you can to enhance the accumulated heat around your plants. A clear overhead tunnel sheltering the plants can help. As the tomatoes develop, a number of leaf problems may also arise. Sometimes you'll see tomato leaves curled up, rolled inward lengthwise along the center vein. This is a normal reaction to cool night temperatures. Generally, the leaf will stay a healthy green and there's no reason to worry about this symptom.
Another common difficulty affects the surface of fruit, both green and ripe tomatoes. This problem results in fruits that turn brownish or black at the bottom (blossom) end, the opposite end its attachment to the stem. The damaged area is flush with the surface of the fruit and stays localized at the blossom end, and gives this problem its name: blossom end rot. This rather ugly difficulty isn't caused by a disease organism. It's the result of the plant not being able to take up calcium from the soil, and it's often caused by dry soils. The problem can be worse on sandy soils which are difficult to keep evenly moist. Be sure, when planting tomatoes, that the soil pH is between 6.5 and 7.0 for tomatoes. Getting a soil test and liming the soil in fall will help to prevent occurrences of this problem in the next growing season by making more calcium available to the plant.
"Catfacing" somewhat resembles blossom end rot, and occurs at the same area on the tomato. But it's has a definite, unique appearance. The blossom end will be misshapen, with irregular swellings and cavities extending into the center of the fruit. This isn't an insect or disease problem. It's possibly caused by cold night temperatures, or by excess nitrogen fertilizer. Some tomato cultivars, including 'Oregon Spring', are affected by catfacing regularly.
Both catfacing and blossom end rot can leave the cook with some edible bits of the tomato, though they may be small depending on the severity of the problem. But if the disease called 'late blight' occurs, the crop may be totally lost. Late blight is caused by a fungus, Phytophthora infestans, the same disease organism, in fact, that caused the death of entire potato crops in the 19th century, setting off the Irish potato famine. Tomatoes, potatoes, and eggplant are all in the same plant family, the Solanaceous plants.
Late blight can move very rapidly through plantings. People who wrote on the Irish potato losses often commented that a healthy field on Monday could be totally dead by Friday. It begins with leaf stalks bending, followed by water soaked 'greasy' looking brown to purplish colored spots on the leaves and stems. There may also be a ring of velvety white ring of mold around the spots and a yellow halo as well. The tomato fruit will develop green water soaked spots which rapidly decay, making the fruit useless and inedible.
Late blight affects all leaves new and old. Signs of late blight will be checked somewhat by dry weather. If it's possible to keep tomato leaves dry, this can help prevent late blight. WSU Master Gardener who have been growing their tomatoes under clear plastic report lower incidences of late blight, and sometimes are able to prevent it altogether. Space, stake, and groom tomatoes to allow as much air circulation as possible. Pull out and destroy any "volunteer" tomatoes and any dead tomato foliage, because these can carry the infection through winter and infest next year's plants. Copper sprays also can help to reduce the disease occurrence, but should be applied before any symptoms are visible. Two copper sprays registered for home use are 'Kop-R-Spray' and 'Bravo Weather Stik.'
Let's hope the rest of the summer is brilliantly sunny, clear, and free of distressing tomato problems.
Hortsense: Managing plant problems with Integrated Pest Management
