A method of protecting plants and seeds thereof which are susceptible to attack by microorganisms. To the plant or seed is applied a compound having the formula (I): wherein R and R min are independently hydrogen or alkyl of 1 to 4 carbon atoms, and R" is (a) hydrogen, (b) a halogen atom F, Cl, Br or l, or (c) a nitro group, or a salt of the compound. The method disclosed is especially useful for protecting ornamental plants, vegetable plants and cereal crop plants and seeds thereof which are susceptible to attack by microorganisms. A composition containing the compound of formula I for use in protecting plants which are susceptible to attack by microorganisms is also provided.