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Gardening: Tomato problems

gardening by Mary Robson, WSU Extension Agent
Although tomatoes are a backyard gardener's most popular vegetable, they are certainly not the easiest to grow.
   In the Puget Sound area, we don't get as much heat as tomatoes prefer. We have to choose the right short-season varieties and then coddle them a bit. Eventually, we get ripe tomatoes so delicious that they make all the trouble worthwhile. That is, we do unless the tomatoes get diseased.
   The worst disease in our region is late blight. This fungus disease strikes towards the end of summer. I have already seen it in community gardens this year. Dark, dead areas appear on leaves, stems, and fruit. The vines may collapse as though hit by an early frost. Infested green fruit rots before it ripens.
   This disease does have one requirement that the gardener can use to protect tomatoes. There must be free moisture on the plant for the spores to infest. The goal, therefore, is to keep the plant dry.
   Staking the plant off the ground is essential. Water it only at the base. Drip or soaker hose irrigation is perfect; it wets the soil, not the plant. I even recommend removing the lower leaves that touch the ground.
   Unfortunately, rain dampens tomato plants and may allow the diseases to get started. I know numerous gardeners who are growing tomatoes under clear plastic shelters of one sort or another.
   Assuming your tomatoes are exposed to rain, the plants must be able to dry quickly after it stops. This means thinning and spacing the vines for the best possible air circulation around them.
   Several fungicides can be used to combat late blight. One of the ones used by commercial growers is available to home gardeners under the name Daconil. Organic gardeners may want to try fixed copper or Bordeaux sprays. Read and follow product labels carefully. These must be applied before the disease gets started, and plants will need multiple treatments.
   If you start seeing symptoms on a few leaves, pick those off and get rid of them. You may be able to hold the disease at bay long enough to get a few more mature fruits. Be sure to clean up and dispose of diseased vines as soon as possible. Do notcompost them.
   As though late blight was not enough, tomatoes have a variety of problems with cultural or environmental causes.
   Blossom end rot is very common. It causes dark, leathery, sunken blotches on the bottoms of your ripening tomato fruit. The problem is considered a nutritional disorder, since it is caused by lack of calcium in the growing fruits. Practically speaking, however, the cause is usually lack of proper irrigation.
   To avoid problems: Visit WSU's Agriculture Site on the World-Wide Web at http://www.cahe.wsu.edu.