Simazine mixtures for control of annual grasses in pastures

Abstract

The effectiveness of tank mixes of simazine plus paraquat, and simazine plus fluazifop-P, for control of annual grass weeds in subterranean clover (Trifolium subterraneum L.) pastures was compared in 6 field experiments in southern New South Wales between 1989 and 1991. Mixtures of simazine (500-750 g a.i./ha) plus very low rates of paraquat (40-60 g a.i./ha) gave better than 90% control of vulpia [Vulpia bromoides (L.) S. F. Gray and V. myuros (L.) C. C. Gmelin], barley grass (Hordeum leporinum Link), annual ryegrass (Lolium rigidum Gaud.), and great brome (Bromus diandrus Roth) and were at least as effective as mixtures of simazine plus fluazifop-P (53-106 g a.i./ha). Subterranean clover plant density was not affected by any treatment. Excellent control of grasses caused increased subterranean clover dry matter yields at 1 site and no differences at another site. In weed-free conditions, 12 of 21 herbicide treatments damaged subterranean clover (severe leaf burn and retarded growth) and significantly (P<0.05) reduced dry weight, but this was not reflected in subsequent seed yields.