The present invention relates to the use of novel oxadiazoles of the formula I or an N-oxide and/or their agriculturally useful salts for controlling phytopathogenic fungi, or to a method for combating phytopathogenic harmful fungi, which process comprises treating the fungi or the materials, plants, the soil or seeds to be protected against fungal attack, with an effective amount of at least one compound of formula I or an N-oxide or an agriculturally acceptable salt thereof; and to agrochemical compositions comprising at least one such compound and to agrochemical compositions further comprising seeds.