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Blossom End Rot is a consequence of a calcium deficiency of a plant, affecting tomatoes, melons, cucumbers, squash, and peppers. Blossom End Rot doesn’t spread between plants and isn’t a condition that can be corrected by using pesticides or fungicides. When Blossom End Rot first begins, you’ll notice a softening of the fruit in a small spot at the blossom end (end opposite the stem). The spot will become brown and watery, enlarge, darken, and then turn black and flattened.   

Photo by Chris Pagliarulo & Gene Giacomelli; UVM Center for Teaching and Learning DSpace Repository

  Causes of Blossom End Rot

  • It can be brought on by sudden drought when the roots of the plant can’t bring water and calcium to the developing fruit.
  • Overwatering and downpours can leach calcium from the soil.
  • Installing plants in substandard conditions can also bring on End Rot by impairing the plant’s ability to establish an adequate root system.
  • Soils with an overabundance of salts can bring on rot because salts will diminish the availability of calcium.
  • High nitrogen plant food can make the problem worse.

How to Avoid Blossom End Rot

  • Use a mix of soils and composts for planting, which are well draining and aerated so plants can easily develop healthy roots. If soils are too heavy, roots may have a difficult time establishing themselves.
  • Don’t rush tomato growing by planting in colder soils. Wait until temps are warm enough to plant tomatoes out. When planted in cold heavy soil, tomatoes have a very good chance of developing Rot.
  • Make sure to check watering when the weather is hot or there are drying winds present.
  • Mulching around plants can help by keeping moisture near the roots.
  • Use food that’s high in superphosphate and low in nitrogen and you’ll lessen the chances for Blossom End Rot

What to do Once End Rot Starts

  • Once the problem has begun, you can use Bonide Rot-Stop, which is calcium chloride sprayed on the foliage; however, nothing will replace good tomato growing practices.
  • Pick affected fruits so the plant can send energy to healthy fruits.
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