Blossom End Rot
Calcium deficiency (physiological disorder, not pathogenic)
Overview
A physiological disorder (not a pathogen) of tomatoes, peppers, squash, and watermelons caused by calcium deficiency in developing fruit, typically triggered by inconsistent watering.
Symptoms
Dark, sunken, leathery patch at the blossom end (bottom) of fruit. Starts as small, water-soaked area that enlarges and turns dark brown to black. Affects first fruit clusters most severely. Secondary mold may colonize affected areas.
Environmental Conditions
Hot
Prevention
Maintain consistent, even soil moisture with mulching and regular watering. Avoid over-fertilizing with nitrogen. Ensure adequate calcium in soil. Avoid damaging roots during cultivation.
Management
Water deeply and consistently. Apply mulch to maintain even soil moisture. Foliar calcium sprays provide limited benefit. Remove affected fruit. Avoid excessive nitrogen. Lime acidic soils.