Compositions containing one or more tyrocidines, tryptocidines, phenycidines and/or gramicidin S, or derivatives and analogues thereof, are described for controlling antimicrobial growth on plants, plant material or plant growth media, and methods for controlling or preventing the growth of microbial pathogens, and in particular fungal pathogens, on plants, plant parts and plant material are described herein. The active agents used to control these pathogens are tyrocidines, tryptocidines, phenycidines and/or gramicidin S, or derivatives, analogues or modifications thereof. The tyrocidines, tryptocidines, phenycidines and/or gramicidin S are cyclic decapeptides having the general amino acid sequence cyc/o(valine-Xrleucine-D-phenylalanine- proline-X
2 -X
3 -X
4 -X
5 -X
6 ) (SEQ ID NO: 1 ) or a derivative or analogue thereof, wherein X
1 is ornithine or lysine, X
2 is valine, leucine, isoleucine, phenylalanine, tryptophan or tyrosine; X
3 is the D-isomer of valine, leucine, isoleucine, phenylalanine, tryptophan, tyrosine, ornithine, or lysine; X
4 is asparagine, glutamine or leucine; X
5 is glutamine, the D-isomer of valine, leucine, or isoleucine; and X6 is tyrosine, phenylalanine, tryptophan or proline.