How Can I Control or Treat Blossom End Rot?

D.S.West VirginiaAnswer: Thank you for your recent request for information from ATTRA, the National Sustainable Agriculture Information Service regarding blossom end rot in your tomatoes.Blossom end rot is a physiological disorder of tomatoes and other vegetable fruits that is typically a result of Calcium deficiency and dry soil conditions. The drought that you mentioned can exacerbate this problem. This disease does not spread from plant to plant in the field, nor from fruit to fruit in transit. Since it is physiological in nature, fungicides and insecticides are useless as control measures.Calcium chloride can be used in an emergency situation and is allowed by the National Organic standards for this purpose. However, it can be toxic to plants, so extreme caution should be used when spraying it and follow the directions on the label. Below are some preventative and cultural tips to employ next year.

  • Plant healthy tomatoes into the field. They should not be excessively hardened nor too succulent when set out.
  • Plant tomatoes in warm soil when possible. Tomatoes planted early in cold soil are likely to develop blossom end rot on the first fruits, with the severity of the disease often subsiding on fruits set later.
  • Irrigate evenly and sufficiently on a weekly basis. Irrigation must be sufficient to maintain a steady even growth rate of the plants. Mulching of the soil is often helpful in maintaining adequate supplies of soil water in times of moisture stress.
  • Avoid excessive use of nitrogen fertilizer. The succulent early growth from this can cause blossom end rot. Use of fertilizer low in nitrogen, but high in phosphate.

References:Sherf and Woods. 1997. Blossom End Rot of Tomatoes. Cornell Cooperative Extension