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Tomato cracks are often caused by drought followed by a heavy rain or watering.

If your tomato crop isn't all you hoped it would be, let’s look at what issues might be in play and how to deal with them.

Tomatoes suffer from many diseases caused by bacteria, viruses and fungi that are helped along by several pests. Check the 2020 Louisiana Plant Disease Management Guide for a complete list of disease symptoms and treatments at the LSU AgCenter's website.

Here are common tomato problems not related to disease: 

The soil — Tomatoes grow best in well-drained soils. But don't always plant your tomatoes in the same spot. To help control soil-related diseases, tomatoes should be rotated out of an area or container every year for three years and replaced with another crop such as squash, beans or corn. Don't plant tomato-related vegetables such as potatoes, peppers and eggplant. 

Blossom-end rot — The telltale sign is a sunken black spot on the bottom of the fruit where the blossom once was. The spots become enlarged by decay-causing organisms. Try using a soaker hose or drip irrigation to help with consistent water delivery to allow the plant to efficiently process the calcium that is also associated with blossom-end rot. 

Many people add Epsom salts to the garden, but this practice actually may promote blossom end rot. Potassium or magnesium will compete with calcium for uptake by the plants. Do not add Epsom salts unless a soil report indicates a deficiency.

Treat blossom end rot by using limestone applied three to six months before planting or adding gypsum (calcium sulfate) applied to the soil at 1 to 2 pounds per 100 square feet. The soil pH should be 6.5. A calcium nitrate side-dress fertilizer is usually the best choice, and is applied monthly at 2 pounds per 100 feet of row. You can also apply gypsum at 1 to 2 pounds per 100 square feet as a side-dress treatment.

Calcium deficiency — In combination with problems caused by over- or underwatering; high humidity; and rainy or cloudy weather, calcium deficiency can be exacerbated by excess ammonia forms of nitrogen (ammonium sulfate and ammonium nitrate) in complete fertilizers such as 10-10-10, potassium or magnesium because they compete with calcium for uptake in the plant.

The practice of adding eggshells, which are a source of calcium, isn't helpful because the mineral won’t be available in time to help with current issues. You are better off composting eggshells and amending your soil with compost with each crop rotation. 

Growth cracks — Just as with blossom-end rots, tomatoes crack when they have uneven watering. Drought followed by heavy rain or watering encourages rapid growth during ripening, leading to cracks in the fruit. Some cracks may be deep, allowing decay organisms to enter the fruit and cause it to rot. Prevent cracks with regular watering.

Poor fruit set — Many reasons, including extreme temperatures and drought, can cause fruit not to set. The blossoms drop off without setting fruit when temperatures are below 55 or above 90 for extended periods. Look for heat-set varieties, such as Solar Fire Hybrid, Florida 91 Hybrid (very reliable), Phoenix, Sun Chaser, Sun Leaper, Solar Set, Sunmaster and Bella Rosa. Not enough sunlight — less than six hours of sun a day — and excessive nitrogen that promotes leaf growth at the expense of blossoms can also prevent fruit from setting.

Herbicides — Herbicides can drift from nearby sprays, causing leaves to whiten or yellow. Use herbicides on days with little wind and try targeted sprayer nozzles to minimize drift.

Leaf curling — This upward curling of lower, older leaves happens during prolonged high temperatures and drought. There's not much you can do. These plants have come to the end of their life due to heavy yields and increasing temperatures. It’s just time to plant heat-set tomatoes like those listed above.

For more information, search tomato on the AgCenter website, lsuagcenter.com.


Email questions to gardennews@agcenter.lsu.edu.