Substituted triazolopyrimidines of the formula I in which the substituents are as defined below: L is hydrogen, chlorine or bromine; R1, R2 are hydrogen, alkyl, haloalkyl, cycloalkyl, halocycloalkyl, alkenyl, haloalkenyl, cycloalkenyl, halocycloalkenyl, alkynyl, haloalkynyl or phenyl, naphthyl or a five- or six-membered saturated, partially unsaturated or aromatic heterocycle which contains one to four heteroatoms from the group consisting of O, N and S, R1 and R2 together with the nitrogen atom to which they are attached may also form a five- or six-membered heterocyclyl or heteroaryl which is attached via N and may contain a further heteroatom from the group consisting of O, N and S as ring member and/or may be substituted as defined in the description; R3 is alkyl, haloalkyl, alkenyl, haloalkenyl, alkynyl, haloalkynyl, cycloalkyl, halocycloalkyl or phenylalkyl; R1, R2 and/or R3 may be substituted as defined in the description; X is halogen, cyano, alkyl, haloalkyl, alkoxy or haloalkoxy; processes and intermediates for preparing these compounds, compositions comprising them and their use for controlling phytopathogenic harmful fungi.