Plant Pathology Infobytes
July 7, 1999
Blossom-end Rot of Tomato - Take Corrective Action!
What's going on with my tomato fruit? The bottom is turning black, and I've lost a good many fruit over the past week. How can I correct this problem?
The above is a common question received by County Extension Offices, and the symptoms described are the result of blossom-end rot, a non-parasitic disease. Blossom-end rot is caused by a shortage of calcium in developing fruit due to a lack of uptake of this essential growth element from the soil. Tomato plants growing in soil low in calcium content and improperly watered are more likely to be produce blossom-end rot affected fruit. It's best to try and keep the soil moisture as even as possible and avoid letting soils dry out before watering. Also, blossom-end rot is generally more severe when plants are fertilized too heavily with nitrogen.
The problem occurs at any stage of fruit growth but is most common on fruit one-third to one-half grown. The first symptom of blossom-end rot is a slight discoloration, water-soaked in appearance, occurring at the blossom-end (bottom) of the fruit. This area enlarges rapidly, producing a dark brown or black sunken area. The skin over the affected area becomes dry and leathery.
The following control recommendations will reduce the amount of tomato fruit lost to blossom-end rot:
- Since this problem is closely related to water supply, it's important to monitor soil moisture and irrigate before signs of moisture stress are apparent. As a general rule, tomato plants need at least one inch of water per week in the form of rain or supplemental irrigation.
- If your plants aren't mulched, consider doing so, since this practice will help maintain uniform soil moisture conditions.
- Apply several sprays of calcium chloride (available at garden supply stores under a variety of trade names) if the disease begins to develop. Follow label directions. Sprays containing calcium chloride will help to prevent further development of the problem but will not cure fruits already affected.
- Follow a recommended program of fertility and avoid excessive application of nitrogen fertilizer.
- Collect a soil sample to determine levels of calcium and correct any deficiency problem through application of lime this fall.
- Remove fruit showing symptoms of blossom-end rot when the problem is first observed. This practice will reduce the drain of food and nutrient materials which otherwise would be available for development of other fruit not affected by blossom-end rot.
If you have questions about blossom end-rot, or any other gardening problem, give us a call at your county Extension office.
Infobytes newsletter was written by the late Dr. Frank Killebrew, Extension Specialist.