There are a number of diseases, cultural and environmental problems that can hurt tomatoes. Blossom end rot is a common issue in many vegetable gardens. It can affect tomato, pepper, eggplant and watermelons. The first symptoms appear as a small water-soaked area at the bottom end of the fruit. This may be seen while the fruit is still green or during ripening. As the lesion develops, it enlarges and becomes black and leathery. In severe cases, the rot can cover the entire lower half of the fruit.
The root cause of Blossom-end rot is a low concentration of calcium in the tomato fruit. When the rapidly-growing fruit of a tomato is deprived of calcium, the fruit tissues break down, leaving a dry, sunken lesion at the end opposite the stem. Several things help contribute to Blossom-end rot.
Low soil pH can inhibit the plant from taking up available calcium in the soil. Using too much ammonia-based nitrogen fertilizer can reduce calcium uptake by providing excess ammonia particles. Water stress is also a major factor for blossom-end rot. Calcium moves into a plant by water uptake, so deficient watering can greatly increase the disorder.
There are several things you can do to help prevent or manage Blossom-end rot. A soil test will tell you how much lime and fertilizer is needed. If you haven’t had your soil sampled, you can add gypsum (calcium sulfate) or lime to the soil at planting. Mix a cup in each planting hole or use one pound per 100 square feet. You can also apply this once you see the problem, but these treatments work slowly. Plants often appear to grow out of the problem as growing conditions improve. Be sure to plant your tomatoes in well-drained soils that are tilled 8 to 12 inches deep. Make sure your plants are receiving 1 inch of water per week. Mulch will help conserve moisture levels in the soil.
If needed, feed your tomatoes once every five weeks. Use fertilizers that have a higher percentage of nitrate nitrogen and smaller levels of ammonia nitrogen. Check the fertilizer label for this information. You may choose to use a 10-10-10 or 5-10-15 fertilizer for side dressing. Try and wait until young tomatoes are the size of a quarter before you side dress. Use caution when cultivating or hoeing.
There are foliar calcium sprays you can apply to the foliage and fruit of the plant. These don’t work as well as soil-based calcium because plants normally take in calcium through the roots. It is preferable to drench a solution of calcium chloride or the foliar calcium spray around the base of the plant.
Tripp Williams, Columbia County’s agriculture and natural resource extension agent, can be reached at (706) 541-4011, or firstname.lastname@example.org.