Blossom End Rot

Encyclopedia Article

Overview of blossom end rot

Blossom end rot is most often found on tomatoes, but also may occur on peppers and summer squash.  This disease can lead to premature ripening as well as inedible fruit. 

Image of blossom end rot on tomato.
Blossom end rot on tomato 

Signs and symptoms of blossom end rot 

Blossom end rot is characterized by water-soaked areas that appear on the blossom end (bottom) of the fruit. The affected tissue desiccates, becoming brown and leathery. Secondary fungi and bacteria may colonize the dead tissue, causing it to turn dark and rot. Blossom end rot is most common on the earliest maturing fruit that ripen in July and early August. 

Blossom end rot is caused by a calcium deficiency in developing fruit. Fluctuating soil moisture due to overwatering or drought, high nitrogen fertilization, and root pruning during cultivation are conducive to blossom end rot.

Type of Sample Needed for Diagnosis and Confirmation

The Iowa State University Plant & Insect Diagnostic Clinic can help you to investigate and confirm if your plant has this disease. Please see our website for current forms, fees, and instructions on collecting and packing samples. Contact information for each states diagnostic laboratory for U.S. residents.  If your sample is from outside of Iowa, please do not submit it to the Plant & Insect Diagnostic Clinic without contacting us.

Management of blossom end rot

This is a problem born of calcium deficiency, most often the result of erratic watering. When the plant is allowed to get too dry or given too much water over periods of time then its ability to uptake calcium from the soil is diminished. To reduce blossom end rot, water tomato plants on a weekly basis during dry weather to provide a consistent supply of moisture to the plants. (Tomato plants require about 1 to 1.5 inches of water per week during the growing season.) Mulch the area around tomato plants to conserve and maintain uniform soil moisture levels. Also, avoid applying large amounts of nitrogen to tomatoes as excessive nitrogen fertilization may contribute to blossom end rot. Adding calcium to the soil is generally ineffective.

Pick and discard fruit affected with blossom end rot. The removal of the affected fruit will allow the tomato plant to channel all of its resources into the growth and development of the remaining fruit.