Blossom-End Rot in a Rabi Tomato Crop
A young farmer in Patna district has 0.4 ha of tomato (cv. Pusa Ruby) transplanted on 10 January. The crop is at the marble-to-green fruit stage. About 15% of fruits show a brown-to-black, sunken, leathery patch at the blossom end; the patch has no fungal growth or bad smell, and leaves look normal. The field was fertilised with 100 kg DAP and 50 kg MOP per ha at transplanting and 40 kg urea per ha at 30 days. Soil pH is 7.8 and EC 1.8 dS/m. Irrigation is by flood every 10 days; the last week was hot and dry with maximum temperatures of 36–38°C. The farmer has bought calcium nitrate and wants to spray it twice a week, and he also plans to spray a fungicide because he fears the rot will spread to healthy fruits.
1. Diagnose the disorder and explain why the farmer's plan of repeated calcium nitrate sprays and a fungicide is not the main solution.
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The patch is at the blossom end, is sunken and leathery, has no fungal growth or foul smell, and the leaves are normal. That pattern points to blossom-end rot, a physiological disorder caused by inadequate calcium supply to the developing fruit, not by a pathogen. Calcium is phloem-immobile and moves mainly with the transpiration stream; fast-growing fruit, fluctuating soil moisture, high salinity and competition from potassium, magnesium or ammonium can all reduce calcium delivery to the fruit even when soil calcium is present. Spraying a fungicide will not help and adds unnecessary cost. Repeated calcium nitrate sprays twice a week are also unlikely to be the main fix: calcium moves poorly from leaf sprays to fruit, and over-spraying can cause leaf burn. The priority is to stabilise moisture and reduce the factors competing with calcium.
2. Give a practical irrigation and nutrition plan for the next 3 weeks, including quantities.
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Change irrigation from one heavy flood every 10 days to light irrigation every 5–6 days, preferably early morning, so that soil moisture remains even; avoid both drought and waterlogging. Apply a 5 cm straw mulch to reduce evaporation. Do not add more MOP, because potassium competes with calcium and the field already received 50 kg MOP/ha; also avoid ammonium sulphate or large urea doses. Apply gypsum at 200 kg/ha, because it supplies calcium without raising the already high pH of 7.8; lime would be wrong here. A foliar spray of 0.5% calcium nitrate (5 g/L) at 7–10-day intervals for 2–3 sprays can reduce new fruit damage, and a small amount of boron can improve calcium movement if boron is low. Existing affected fruits will not recover.
3. Should he remove the affected fruits and spray fungicide? What else should he check?
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Yes, remove the affected fruits; they cannot recover and may become entry points for secondary rot organisms. But do not spray a fungicide as a routine treatment for blossom-end rot. A fungicide is justified only if there is actual secondary infection or another diagnosed disease. He should also check the irrigation water and soil EC; 1.8 dS/m is moderate but can aggravate calcium uptake if it rises. Check drainage, avoid deep flooding, and keep a record of which new fruits develop symptoms after the irrigation change. If new symptoms continue despite even moisture, test for boron and calcium and check root health, including nematode damage.