Disclosed is a method of inhibiting the growth of perennial forage grasses which comprises contacting the perennial forage grass or the locus thereof with a growth inhibiting amount of pyroxsulam which is also known as N-(5,7-dimethoxy[1,2,4]triazolo[1,5-a]pyrimidin-2-yl)-2-methoxy-4-(trifluormethyl)pyridine-3-sulfonamide.