Long spelling periods are required for pasture to become free of contamination by infective larvae of Haemonchus contortus in a humid subtropical climate of São Paulo state, Brazil.

•In Botucatu, Brazil, Haemonchus larvae was recovered from the pasture in all season.•Environmental contamination persisted for almost a year in autumn and winter.•The pasture contamination persists for 294 days in spring and 182 days in summer.