fungicidal compositions for controlling fungus diseases in plants are disclosed . these compositions contain as their active materials compounds and polymers thereof corresponding to the formula : ## equ1 ## in which y &# 39 ;, y &# 34 ;, z &# 39 ; and z &# 34 ; represent a hydrogen atom or an optionally halogenated alkyl radical containing from 1 to 5 carbon atoms . included within these active materials are the hydrolysates , salts and quaternary salts of these phospholanes . these cyclic phospholanes or phosphites and their hydrolysates are compatible with other commercial fungicides and the compositions disclosed include these compounds above and in combination with such other fungicides .