What’s ailing your tomatoes?

Jul 13, 2014
By this time of year, gardens generally look good but problems seem to plague certain vegetables. Of all the plants in the garden, people seem to be most concerned about their tomatoes.

One common problem is leaf curl. Developing leaves become thick and curled but remain green. This is actually a problem caused by irregular watering—too much water followed by too little. The leaves respond by growing thicker and curling. Because the problem is related to the availability of water, leaf curl usually clears up as new leaves develop.

Curled tomato leaves can also be a symptom of herbicide damage to the plants. Tomatoes are very sensitive to weed killers used on lawns. A very fine mist of weed killer is enough to curl tomato leaves. Lawn herbicide applied on hot days can also give off herbicide vapors that will cause damage. In all of these herbicide-damage cases the leaves are usually thin and strap-like.

Small amounts of herbicide containing glyphosate can also cause damage. This very common herbicide is used for non-selective killing of weed and grass in gardens, walkways and landscapes. A less than lethal dose of glyphosate will cause abnormal growth of tomato leaves. In this case, however the leaves are curled with bleached (white) areas, usually at the tips.

Catfacing is another common problem and will likely show up on plants that were exposed to cold weather early in the season. Catfacing is a series of creases or cracks on the blossom end of the fruit. These cracks meet and cross one another or form rings at the bottom of the fruit. Small undeveloped fruits that were damaged by early season cold are marred as they mature later in the year. A deeply cracked and blemished fruit may be attacked by fungus or other rot organisms, but firm, ugly fruit can still used.

Blossom end rot is another condition that shows up in early tomato harvests. Low calcium in the developing fruit causes the blossom-end (bottom) of the fruit to collapse. The entire bottom will turn black but remain somewhat firm. As with catfacing, bacteria and fungus can attack the damaged fruit making it unusable.

To treat for blossom end rot one must increase the calcium available to the plant. A soil test will help determine calcium levels and the pH of the garden soil. Lime can be added to the garden—this will raise the pH and add calcium to the soil. If the garden already has a high pH, gypsum can be added as a source of calcium without changing the pH. Regular watering can also help the plant maintain a healthy calcium level. Also, do not overfeed the plant as that might worsen the blossom end rot problem.

During the hottest days of summer tomato plants may wilt. The roots are unable to supply enough water to the leaves. Overnight, the roots catch up and the leaves recover. When cooler weather returns the plant will go through the entire day without wilting.

In spite of the problems, tomatoes are still one of the favorite and most rewarding garden vegetables to grow.