Cookies on Plantwise Knowledge Bank

Like most websites we use cookies. This is to ensure that we give you the best experience possible.


Continuing to use means you agree to our use of cookies. If you would like to, you can learn more about the cookies we use.

Plantwise Knowledge Bank

Your search results

Plantwise Factsheets for Farmers

Minerals against blossom end rot in tomato


Recognize the problem

Blossom end rot is not a disease. It is a plant disorder caused by a lack of calcium in the flowers and fruits. The first symptoms of end rot are a water-soaked area near the blossom scar of the fruit. This area later develops into a larger, tan to brown, leathery lesion. Fungi often colonize these lesions, which make them grey to black and velvety. Although blossom-end rot is often seen on mature fruits, young, rapidly growing fruits are most endangered by calcium deficiency.


Blossom end rot is a result of insufficient calcium uptake by the plant. This usually occurs as a result of quick changes of periods of wet and dry soils. Other factors are boron deficiency, high salt content in the soil, irregular or over irrigation, high fruit load, or too much nitrogen. Foliar-sprayed fertilizers with calcium and magnesium can be used against this disorder. CALMABON is one of these fertilizers and contains Nitrogen, Calcium, Magnesium, Boron and Molybdenum, all of which are needed by the plant. For comparable products, contact local agro-input dealers.


  • Ensure the plants always have a good supply of water
  • Buy your CALMABON Plus or comparable calcium-magnesium fertilisers for vegetables from a registered agro-dealer
  • Use 500 ml - 1600 ml CALMABON-Plus per 100 litres of water, translating to 5 to 8 litres per hectare. This means 100ml - 320ml of CALMABON-Plus per 20 litres of water of knapsack sprayer.  But double check product label for dosage instructions, as products may differ.
  • Add 2 tablespoons of sticker (teepol/any liquid soap) per 20 litres to allow the mixture to stick on the leaves. Mix properly.
  • Use fine flat spray nozzles, to apply a full coverage foliar spray.
  • Make first spray at flowering stage and repeat every second week, if required.  Do not spray at shorter intervals than 10-14 days.
  • Spray especially when plant transpiration is reduced by factors like changes in temperature (warmer or colder).
  • Spray mid-morning when there is no dew or late afternoons when there is no wind. 

The recommendations in this factsheet are relevant to: Zambia

Authors: Mooya Nzila
Zambia Agriculture Research Institute ZARI of Ministry of Agric. And Livestock
tel: +260 966 728668 email:
©CAB International. Published under a CC-BY-SA 4.0 licence.

Plantwise Factsheets Library app

Get all of the factsheets and pest management decision guides from this website in an offline format via the Plantwise Factsheets Library app.