Q: I have several tomato plants with tomatoes that are green and on the vine. On some, but not all of them, the tomato fruits have a big black spot on the bottom.
I’m afraid this is a fungus that will spread to the other plants. What can I do?
A: Sounds to me like you have blossom end rot. The condition is caused by a lack of calcium in the plant when the tomatoes are the size of marbles. You can stop the problem on currently affected plants but you’ll have to throw away the tomatoes that are bad now.
Use a calcium chloride spray (Stop-Rot, etc.) to help cure this disorder. Begin spraying plants when the first fruit cluster is seen. Apply calcium chloride every 7 to 10 days until 4 applications have been applied. Spray plants until solution drips off the plant.
How to prevent blossom end rot in the future? My friends at Fort Valley State University make these recommendations:
1.Select a planting site that has well-drained soil and is in a sunny location.
3.Mix one-half cup of lime with the soil going back into the hole dug for plants.
4.Mix one-half cup of superphosphate (0-46-0) with soil around each plant.
5.Don’t overfertilize tomatoes at setting. Mix one cup of 6-12-12 or 5-10-15 into the soil in a 2 by 2 foot area for each plant.
6.For the rest of the summer, fertilize with calcium nitrate rather than ammonium nitrate.
7.Mulch plants with pine needles, old leaves, grass clippings, etc., to conserve water and provide more uniform soil moisture for the plant.
8.Unpruned plants will have less blossom-end rot than severely pruned plants.
9.Do not let soil moisture fluctuate between extremely dry and wet. Irrigate plants thoroughly and often enough to maintain a constant, uniform water supply to plants.