Blossom End Rot Blemishes Homegrown Veggies

Date:  July 29, 1997
Editor: D'Lyn Ford  (505) 646-6528, dlford@nmsu.edu

LAS CRUCES -- Gardeners who find brown leathery patches on the bottoms of their tomatoes and peppers can relax. It's not a killer plant disease.

The culprit is blossom end rot, a disorder that crops up when garden plants have an inconsistent water supply, said Natalie Goldberg, plant pathologist with New Mexico State University's Cooperative Extension Service.

"Blossom end rot is a disorder instead of a disease because it's not linked to microorganisms considered disease-causing agents," Goldberg explained.

"It is caused by inconsistent watering and a calcium deficiency in the developing fruit. If plants get too much water and then are allowed to dry out too much, that's the kind of fluctuation that can cause the problem."

Evening out the water supply is the key to preventing blossom end rot. Goldberg recommends keeping the root zone moist enough to easily form a ball. This should be possible even with urban watering limitations, she said. Thorough, deep watering that wets the entire root zone of the plant is better than frequent sprinkling.

"When plants are consistently moist but not too wet, it tends to bring on fewer problems with blossom end rot," Goldberg said.

Because the problem is not caused by a disease, blossom end rot is not contagious. However, other plants growing under the same conditions are susceptible.

Problems typically are worst in the heat of summer.

In New Mexico, the disorder is most common in tomatoes, bell peppers and chile, although it also affects squash and melons, Goldberg said.

Blossom end rot begins as a brown spot that enlarges to cover up to half the fruit as it matures.

With age, the blemish becomes sunken and leathery. Eventually, fungi or bacteria may invade, giving the fruit a black or watery appearance. Affected fruit ripens faster. Though gardeners can always cut away the affected part of the fruit and eat the rest, finding blossom end rot can be discouraging.

To prevent problems next season, Goldberg recommends using mulches that hold in water. She also suggests asking nursery and seed suppliers which varieties are least susceptible to blossom end rot.