August 2014 Plant Disease Update

tomato blossom end rot
Blossom end rot on tomato caused by calcium deficiency to developing fruit. Fungi are secondary on decayed tissue.

The time to harvest luscious, red, vine-ripened, garden tomatoes is upon us! Unfortunately, some gardeners may pluck a red tomato from the vine only to discover that it is brown and rotten on the bottom, or blossom end, of the fruit. This condition is due to a disorder called “blossom end rot”. Although fungi may sometimes be seen growing on the rotted tissue, the problem is not caused by a pathogen. Blossom end rot is caused by a deficiency of calcium to the developing fruits.

Sometimes calcium is lacking in the soil, but more often than not, this condition is a result of uneven water supply or prolonged drought. Lack of water or extremes in water availability reduce calcium transport to the developing fruit. Because calcium is necessary for the structural integrity of the fruit, a breakdown of tissue at the blossom end occurs. Although unaffected parts of the fruit are still edible, the flavor is not as good and overall yield is reduced. 

Pepper blossom end Rot
Blossom end rot on pepper.

Provide an even moisture supply by mulching plants to conserve soil moisture and ensure that plants receive a total of 1.5 inches of water per week during fruiting. Improper soil pH can also lead to calcium deficiency. Maintain a soil pH of 6.0-6.5 by liming and fertilizing according to soil test results. Calcium foliar sprays are also available, but require multiple applications beginning at the time the second fruit clusters bloom. Blossom end rot causes similar symptoms on peppers, although in contrast to tomatoes, the rotted tissue may appear on the side of the fruit near the blossom end rather than at the bottom only.