The present invention relates to co-crystals of pyrimethanil and dithianon, which, in a X-ray powder diffractogram at 25°C show at least three of the following reflexes: 2θ = 7.46 ± 0.20, 2θ = 9.98 ± 0.20, 2θ = 13.28 ± 0.20, 2θ = 23.09 ± 0.2, 0.2θ = 24.38 ± 0.20, 2θ = 27.01 ± 0.20 a process for their preparation and their use for the preparation of compositions for crop protection.
