PHOTO: Jessica Walliser
Jessica Walliser
July 19, 2018

Tomatoes are arguably the most popular garden crop here in the U.S. but they are not without their problems. Thought a big harvest is in the cards for many gardeners, others might face a handful of problems from time to time. Here are some common summer tomato problems and how to overcome them.


1. Blossom-End Rot

This physiological disorder appears as a sunken, dark lesion on the bottom-end (or blossom-end) of the developing fruit. Tomatoes develop blossom-end rot when there is a lack of calcium in the growing fruit. The trouble is not necessarily that your soil is calcium-deficient, but rather that the calcium can’t get into the plant. Calcium comes into a plant with water, and when plants are subjected to dry periods, the calcium cannot move into the fruits where it’s needed for proper growth. This leads to a calcium deficiency and blossom-end rot. The key to staving off this disorder is proper mulching and watering.

2. Curled Leaves

Leaf curl is a physiological problem often related to fluctuations in moisture levels. For many tomato varieties, curling up their lower leaves is a way to protect the plant from further moisture loss by protecting the pores on the leaf surface. Some varieties are more prone to leaf curl than others. If the leaves are blemish-free, leaf curl on the older leaves isn’t anything to worry about. But curling leaves can also be a sign of root wilts, though when these wilts are involved, the entire plant is effected, with every leaf curling and drooping, not just a few. Most often, leaf curl is not one of the summer tomato problems worth worrying about.

3. Blossom Drop or Fruit Drop

Young, developing fruits and/or blossoms are sometimes shed from a tomato plant for a few different reasons. It might occur from lack of proper pollination or because the plant is stressed. Some plants do not set fruit when temperatures aren’t ideal, including tomatoes. Daytime temperatures over 90 degrees F or nighttime temps below 55 degrees will limit tomato production. Not to worry, though, because as soon as the heat or other weather stress passes, the plants will resume production.

4. Fungal Issues

Fungal diseases, such as blights and leaf spots, are probably the most common of the summer tomato problems. Fungal diseases on tomatoes most often appear as tiny, round leaf splotches, yellowing or other blemishes on the tomato plant’s leaves. Sometimes the infection begins on the lower leaves first, while other times the newer leaves are affected first. If you suspect a fungal issue is to blame, take steps to properly ID and treat it. And, be sure to remove diseased plants at the end of the season to prevent the spores from overwintering. Remove and destroy infected leaves as soon as you spot them.

5. Tomato & Tobacco Hornworms

These large, green caterpillars can quickly defoliate a young tomato plant as they feed on the foliage. They are the larvae of nocturnal moths known as hawk moths. Caterpillars can grow up to 5 inches long. Gardeners will often find the dark pellets of caterpillar poop before they see the caterpillars themselves. Missing leaves, combined with the presence of these dark pellets, is a sure sign of hornworms. Thankfully, hornworms often fall prey to non-stinging parasitic wasps that use them as hosts for their young. But, handpicking is also very effective.

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