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±0.202θ=9.98±0.202θ=13.28±0.202θ=23.09±0.202θ=24.38±0.202θ=27.01±0.20a process for their preparation and their use for the preparation of compositions for crop protection.
