The use of nitroethane derivatives of the formula I where: R1 is hydrogen, unsubstituted or substituted C1-C6-alkyl, C3-C6-alkenyl, C3-C6-alkynyl, halogen, cyano or thiocyanato; R2 is hydrogen, formyl; halogen- or C1-C3-alkoxy-substituted or unsubstituted C1-C6-alkylcarbonyl, C2-C6-alkenylcarbonyl, C4-C6-alkyldienylcarbonyl or C2-C6-alkynylcarbonyl; A is unsubstituted or substituted phenyl, naphthyl, quinolyl, quinazolyl, quinoxalyl, 1-methylindolyl, 1-methylbenzimidazolyl, 2-methylindazolyl, benzofuranyl, benzothienyl, benzoxazolyl, benzothiazolyl, furyl, thienyl, pyrrolyl, isoxazolyl, isothiazolyl, pyrazolyl, oxazolyl, thiazolyl, imidazolyl, oxadiazolyl, thiadiazolyl, triazolyl, pyridinyl, pyridazinyl, pyrimidinyl, pyrazinyl or triazinyl, pyranyl or thiopyranyl; as microbicides is described.