The weather so far this spring has been much better than last year for our vegetable gardens. The light, infrequent rain has been great compared to the excessive moisture of last season. While most of us have recently planted our gardens, we need to get a head start on scouting for problems. A common issue in many vegetable gardens is dark, sunken lesions on the bottom tomato fruit. This is a nutritional disorder called "Blossom-end rot."
Blossom-end rot can affect tomato, pepper and eggplant. The first symptoms appear as a small water-soaked area at the blossom 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 very 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. Calcium is a micronutrient that is required in large amounts for normal plant tissue growth. 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. Initial calcium levels in the soil may be low. 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. Most of the calcium has entered the fruit before it is the size of a quarter, so proper watering during early fruit development is crucial.
There are several things you can do to help prevent or manage Blossom-end rot. Add lime to your soil according to your soil test results one to three months before planting. Adding gypsum to your soil will also help raise your pH faster than lime. Plant your tomatoes in well-drained soils that are tilled eight to twelve inches deep. Make sure your plants are receiving one inch of water per week. It is best to water deeply and infrequently. Mulching around your plants will help the soil to retain moisture. Make sure to pull the mulch away from the main stem to prevent stem and crown diseases.
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. Damaged roots will not take up calcium well. Heavily pruned tomatoes are also more susceptible to Blossom-end rot.
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. Calcium doesn't move around well from leaves to fruit, so much of the foliar calcium spray may not be effective. It is preferable to drench a solution of calcium chloride or the foliar calcium spray around the base of the plant.
Clark MacAllister is the Dawson County extension agent. For more information, call (706)265-2442.