July 22, 2016
Our weather, with alternating cooler rainy periods and extreme heat like last week, is setting us up for a number of problems. Nothing is more frustrating to the home gardener than to watch their tomatoes slowly ripen, only to discover the bottom of the fruit has turned black and started to decay.
Blossom-end rot is a serious problem in tomato, pepper, and eggplant. Growers often are disappointed to discover a decay developed on the blossom end (opposite the stem) of many fruit, especially the first fruit of the season. This nonparasitic disorder can be very damaging, with losses of 50% or more in some years.
The symptoms of blossom end rot on tomato and eggplant usually begins as a small water-soaked area at the blossom end of the fruit. This may appear while the fruit is green or during ripening. As the lesion develops, it enlarges, becomes sunken and turns black and leathery. In severe cases, it may completely cover the lower half of the fruit, becoming flat or concave.
Secondary pathogens commonly invade the lesion, resulting in complete destruction of the infected fruit. On peppers, the affected area appears tan, and is sometimes mistaken for sunscald, which is white. Secondary molds often colonize the affected area, resulting in a dark brown or black appearance. Blossom end rot also occurs on the sides of the pepper fruit near the blossom end.
Blossom-end rot is not caused by a parasitic organism but is a physiologic disorder associated with a low concentration of calcium in the fruit. Calcium is required in relatively large concentrations for normal cell growth. When a rapidly growing fruit is deprived of necessary calcium, the tissues break down, leaving the characteristic dry, sunken lesion at the blossom end.
Blossom-end rot is induced when demand for calcium exceeds supply. This may result from low calcium levels in the soil, drought stress, or excessive soil moisture fluctuations which reduce uptake and movement of calcium into the plant, or rapid, vegetative growth due to excessive nitrogen fertilization.
There are several things you can do to manage blossom end rot:
• 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.
• Avoid over applying nitrogen fertilizer during early fruiting.
• Avoid drought stress and wide fluctuations in soil moisture by using mulches and/or irrigation. Plants generally need about one inch of moisture per week from rain or irrigation for proper growth and development.
• Foliar applications of calcium, which are often advocated, are of little value because of poor absorption into the plant and movement to the fruit where it is needed.
If your tomatoes have blossom end rot and it hasn’t damaged the whole tomato, you can remove the damaged portion of the tomato and eat the rest. It does not affect the edibility of the rest of the fruit.
Another problem we frequently see on the first tomatoes of the year is a disorder called cat’s face or catfacing. This is a distortion of the fruit with deep creases and misshapen fruit. This is an environmental disorder so you can not treat for it. It can be caused by wide fluctuations or extremes in air temperatures (hot or cold) and variations in moisture availability in the soil. It is usually seen on the first tomatoes on a plant.
Catfaced tomatoes should be removed because they will not ripen evenly. By removing them, the plant does not “waste” it’s energy on those tomatoes that will not produce usable fruit and will use it to produce unaffected tomatoes.
For more information on blossom end rot or catfacing on tomatoes, contact your local Nebraska Extension office.
Tomato Blossom End Rot