Evaluation of herbicides for control of summer-growing weeds on fallows in south-eastern Australia

Abstract

Eighteen herbicides or herbicide tankmixes were evaluated over 3 years (1987-89) for their control of 11 important summer-growing weeds on fallows in southern New South Wales and the Wimmera area of Victoria. Each of the weeds was effectively controlled by at least 1 herbicide. The tank-mixes of glyphosate plus metsulfuron (270 + 4.2 g a.i./ha) and glyphosate plus 2,4-D ester (270 + 320 g a.i./ha) were the most effective treatments, each giving an average of 68% control of all species. Hogweed (Polygolzunz avicu1ar.e L.), prickly paddy melon (Cucumis myriocarpris Naudin), spear thistle [Cirsium vulgare (Savi) Ten.] and skeleton weed (Chondrilla juncea L.) were the species most tolerant of these 2 tank-mixes. When these species were exluded, glyphosate plus metsulfuron and glyphosate plus 2,4-D ester gave an average of 90 and 88% control, respectively, of the remaining species [common heliotrope, Heliotropiunz europaeum L.; camel melon, Citrullus larzatus (Thunb.) Matsum. and Nakai var. lanatus; prickly lettuce, Lactuca serriola L.; sowthistle, Sonchus spp.; clammy goosefoot, Chenopodium pumilio R.Br.; caltrop, Tribulus terrestris L.; stink grass, Eragrostis ciliatiensis (All.) E. Mosher]. Hogweed was most effectively controlled by 2,4-D amine plus dicamba (750 + 100 g a.i./ha) or 2,4-D ester (800 g a.i./ha); prickly paddy melon by 2,4-D amine plus triclopyr (750 + 96 g a.i./ha); spear thistle by 2,4-D amine plus dicamba (750 + 100 g a.i./ha) or glyphosate plus clopyralid (270 + 60 g a.i./ha); and skeleton weed by 2,4-D amine plus clopyralid (750 + 60 g a.i./ha). A pot experiment confirmed field observations that, as common heliotrope ages, glyphosate and glyphosate plus metsulfuron become less effective for its control.