Stem Rot / Collar Rot in Tomato — causes, treatment and prevention for Indian conditions.
Sclerotinia stem rot (white fluffy growth + black sclerotia), Didymella stem canker
Carbendazim 1g/L + Mancozeb 2.5g/L spray on stems. Remove heavily infected plants.
Avoid dense planting. Do not wound stems. Remove crop debris.