Rhonda Ferree, Horticulture Educator with University of Illinois Extension, says that she has received many vegetable-related calls lately. “Most of them pertain to the drought we are in. In particular, we expect to see a lot of blossom-end rot this year.”
As the name suggests, blossom-end rot develops at or near the bottom (or blossom end) of the fruit and appears as a slight, water-soaked area. Ferree warns that this disorder can be very damaging, with losses of 50% or more in some years.
“On tomatoes, the area enlarges, darkens, and becomes dry, sunken, flat, leathery, and dark-brown to black.” Various molds and fruit rots may develop within the sunken area. Pepper, summer squash, and other cucurbit crops may also experience this problem.
“Blossom end rot is actually a non-infectious disease that is thought to be caused by insufficient calcium when the fruit are forming,” explains Ferree. Calcium deficiency usually results when nitrogen levels are high, when plants grow rapidly, and when extremes in moisture occur (heavy rains, drought, root injury, etc.).
When soil moisture is limited, plant growth slows, and nutrient uptake by the roots is reduced. If water becomes available again, the plant begins to grow rapidly, but the uptake of calcium lags behind. Thus, the rapidly expanding fruit tip does not have enough calcium available to develop properly, even though there is plenty of calcium in the soil.
Although there is nothing you can do to help the affected fruit, good horticultural practices can help manage the problem.
1. Maintain the soil pH around 6.5. Liming will supply calcium and will increase the ratio of calcium ions to other competitive ions in the soil, but don’t lime if your pH is too low.
2. Use nitrate nitrogen as the fertilizer nitrogen source. The ammonia form of nitrogen may actually increase blossom-end rot because ammonia ions reduce calcium uptake. Avoid over-fertilization as side dressings during early fruiting, especially with ammonia forms of nitrogen.
3. Avoid drought stress and wide fluctuations in soil moisture by using mulches and/or irrigation. Plants generally need about 1 inch of moisture per week from rain or irrigation for proper growth and development.
4. Foliar applications of calcium, which are often advocated, are of little value because of poor absorption and movement to fruit where it is needed.
For more information on common vegetable crop problems go to http://urbanext.illinois.edu/vegproblems.