My previous column, "Picking a Better Tomato," dealt with three tomato problems - fusarium wilt, root-knot and spotted wilt - common in the Lowcountry that can be prevented by growing resistant varieties. Now we'll look at common tomato problems that can be managed with other methods.
Gardeners in areas bordering Charleston Harbor (USDA Zone 9) can set tomato plants in the ground after March 15. April 1 is a safer date for most of the Charleston area, which is in Zone 8b. Later planting avoids nighttime temperatures in the mid-30s that often occur near the end of March or as late as the beginning of April. Temperatures this cold will injure, but probably not kill, young tomato plants.
To protect plants from low night temperatures, cover them with plastic milk jugs with the bottoms cut out and the caps put on. If the jugs are left in place during the day, the caps must be removed, so the plants will not be injured by the high temperatures that build up in these mini-greenhouses.
Tomatoes prefer "slow and steady" water and fertilizer. Like most plants, an inch of water per week is usually enough. When plants have several fruits and temperatures rise, watering should be increased to an 11/2 inches per week. Rainfall, measured in a rain gauge, counts in the weekly water ration. Compost and granular fertilizer should be added to soil at transplanting. Apply half-strength liquid fertilizer every other week.
Disease and disorder
Blossom end rot (BER) is a frustrating disorder seen on the first ripe tomato fruits. Although it is called a rot, it starts as a lack of calcium in the fruit. Calcium can only be absorbed from the soil through the roots as plants absorb water, so a lack of water makes BER worse.
Some Lowcountry soils lack sufficient calcium for tomatoes. To prevent BER, lime must be added to these soils when plants are set in the ground. (This is one reason why Extension agents constantly advise, "Have a soil test done.") Otherwise, do nothing. Calcium sprays applied to leaves do not work.
Tomato plants "learn to make do" with the amount of calcium in the soil by growing more roots to take up more calcium. The second flush of fruit to ripen usually does not have blossom end rot.
Gray leaf spot, a tomato disease that attacks heirloom tomatoes, especially 'Cherokee Purple,' is common throughout the Southeast. It almost disappeared after resistant tomatoes were bred in the 1960s. When susceptible heirloom varieties became popular again, the disease reappeared. No organic sprays will control gray leaf spot. Plants with this disease should be sprayed with chlorothalonil fungicide or removed from the garden and destroyed.
Stink bugs are a common pest on home garden tomatoes. Both green and brown stinkbugs pierce tomato fruit while feeding on it and leave a white, one-quarter-inch, corky blemish under the skin. Neem oil sprays discourage stink bugs from feeding on tomatoes and other vegetables.
The tomato horn worm is a wily pest. Once a gardener sees how much damage one caterpillar can do in a short time, he or she never forgets. The 2-inch-long, fat worm is almost as green as healthy tomato leaves. It hides under the leaves, until it eats so many leaves it has nowhere to hide! Removing caterpillars by hand (while wearing gloves) is the best solution. My preferred method to destroy them is dropping them in boiling water.
Rot and molds
As tomato fruits ripen, they become more acidic. Acid is part of the classic, home-garden tomato flavor. An acidic tomato, however, is more susceptible to molds and rots than a green tomato.
Tomato anthracnose causes ripe tomato fruit left on the kitchen counter to rot. This rot starts as perfectly round, slightly sunken spots on the shoulder (top) of fruit. At this point, there is nothing to do other than to discard the fruit or to salvage the bottom half.
Picking fruit a few days earlier than normal or refrigerating fruit will slow anthracnose, although this may compromise flavor. No organic sprays will control anthracnose. Chlorothalonil sprayed onto green fruit will help prevent it. Rotten fruit must be removed from the garden, so the anthracnose fungus does not carry over to the next season in the soil.
Anthony Keinath is professor of plant pathology at the Clemson Coastal Research & Education Center in Charleston. His expertise is in diseases of vegetables. He also is an avid gardener. Contact him at tknth@ clemson.edu.