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Blossom-End Rot and Sunscald

Blossom-end rot appears as necrotic areas at the blossom end of the maturing fruit. Tomato, pepper, summer squash, and other cucurbit crops may show this problem. Tomato fruit tips turn brown to black; the ends on peppers usually become light brown or tan.

Blossom-end rot is not caused by a pathogen, so it is not an infectious problem. It results from a calcium deficiency in the plant caused by large fluctuations in soil moisture. When soil moisture is limited, plant growth slows and nutrient uptake by the roots is reduced. If water becomes available again, from rain or irrigation, the plant begins to grow rapidly but the uptake of calcium lags behind. In this way the rapidly expanding fruit tip does not have enough calcium available to develop properly, even though there is plenty of calcium in the soil.

The best method for controlling blossom-end rot is to maintain even and adequate levels of soil moisture. In such conditions, plants grow at an even rate and the nutrients stay in balance. Calcium-rich fertilizers show mixed results in controlling this problem.

Sunscald also causes necrotic areas on the fruit of tomato and pepper. The areas of the fruit that are exposed to the sun are susceptible; usual spots are on the shoulders of the fruit near the stem end. Sunscald often occurs when plants lose leaves from foliar diseases or from sudden pruning of the plant canopy.

Avoid sunscald by controlling diseases that cause premature defoliation. This would include the tomato leaf spots discussed in issue No. 9, the vascular wilt diseases, and bacterial canker. Grow tomato varieties that are resistant to Verticillium and Fusarium wilts. Plant pepper varieties that produce fruits that hang down and are covered by foliage. Minimize plant breakage during harvesting to avoid suddenly exposing the fruit to sunlight.

Author: Nancy Pataky


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