Master Gardener: Tomato rot traced to uneven watering
BY BRIAN JERVIS Ask a Master Gardener
Saturday, June 16, 2012
6/16/12 at 5:13 AM
Q. Some of my tomatoes have developed a large brown spot on their ends, the rest of the tomato and the vine look OK. What is this? Chris C., Tulsa
A. Master Gardeners are seeing this daily at the OSU Extension office. Your tomatoes have a condition called "blossom end rot." It is not a disease or insect problem and needs no treatment other than perhaps altering your management of the plants.
Blossom end rot is caused by calcium deficiency in the tomato. Calcium is absorbed by the roots and delivered in the plant by the circulation or flow of sap. If there is not enough calcium delivered to the developing fruit, the part furthest from the stem, the blossom end, can develop a localized calcium deficiency. This will begin to deteriorate and develop a leather-like brown discoloration called necrosis, which may rot.
This problem may occur not only in tomatoes but in several other vegetable fruits such as peppers, eggplant, squash, zucchini and watermelons.
The calcium deficiency is usually not due to a lack of calcium in the soil - our soils have plenty - but is a problem with supply to the fruit. When the circulation is reduced, either due to dry soil or hot and windy weather, the plant tends to send most of the calcium containing sap to leaves and not fruit. Leaves are more important for survival.
Other factors contributing to blossom end rot are roots too small for the plant, overly wet soils and too much nitrogen fertilizer.
Excessive soil moisture smothers roots, preventing calcium absorption. Too much fertilizer causes tomato plants to grow more leaves than tomatoes, directing calcium flow into leaves. The type of fertilizer may also be important - ammonium types of nitrogen fertilizer can interfere with calcium absorption, while the nitrate forms do not.
To prevent the problem, water regularly, but don't overdo it. Most tomato plants need about two inches of water per week in two to three applications. The goal is to moisten the soil down to 12 inches or so. One should avoid daily shallow watering. Also, a 2- to 3-inch layer of organic mulch will help reduce water loss and moderate temperatures.
There are some varieties of tomatoes that are less susceptible to blossom end rot than others; this includes Celebrity, Jet Star, Mountain Pride, Pik Red and Sunny. Consider this group for your next tomato garden.
For more, go to tulsaworld.com/mastergardener. If you have a garden-related question you would like the Master Gardeners to answer in a future column, call 918-746-3701.
Original Print Headline: Water carefully to avoid rot
Garden tips
Spider mites on ornamentals and vegetables may appear this month. They love marigolds and tomatoes. The foliage becomes pale and speckled. They are very small - shake a branch over white paper and watch for specks that crawl. Spider mites need early control. Use powerful jets of water to wash them off plants' leaves and spray with horticultural soaps and/or horticultural oils such as Neem.
With the warm weather, tomatoes will develop problems. Many varieties will become infertile and quit setting fruit when night temperatures are over 70 and daytime over 90. They will be productive again in the fall when temperatures cool. Plants will survive the summer better with a thick layer of mulch and regular deep watering. Tomatoes usually will not develop deep red color when the temperature is over 85 degrees. They will ripen and become red if harvested and brought indoors - no sunshine needed for this.
Associated Images:
Too much water can lead to blossom end rot in tomato plants. It develops if there is not enough calcium delivered from the soil to the fruit of the tomato. BILL SEVIER/for the Tulsa World
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