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Application of glyphosate to conserve annual pasture for grazing during summer

K.L. Gafford, C. Siever-Kelly, B.J. Leury, R.J. Simpson and H. Dove

School of Agriculture and Forestry, University of Melbourne, Parkville VIC 3052
Rutherglen Research Institute, Chiltern Valley Road, Rutherglen VIC 3685
CSIRO Division of Plant Industry, GPO Box 1600, Canberra ACT 2601

Annual pastures in southern Australia are dead throughout summer and early autumn. These pastures are deficient in digestible energy and crude protein (1,4) and are unable to maintain sheep liveweight without supplementary feeding. In annual ryegrass pastures, the yield of digestible dry matter is maximal between heading and anthesis, but falls rapidly as the pasture senesces, mainly due to the loss of cell contents, which are highly digestible (3). Spraying of annual pastures with low rates of glyphosate before anthesis delays the loss of cell contents, resulting in improved pasture quality for some time into summer (2). The aim of the trial was to assess the utilization of this pasture by the grazing animal, and the subsequent effects on animal production.


Annual ryegrass, Lolium rigidum, and silver grass, Vulpia bromoides, pasture was sprayed with glyphosate (180 g a.i./ha as Roundup CT) 16 d before anthesis, at approximately 50% heading (12 October 1990). Sprayed and control pastures were stocked with twelve 18-month-old Merino wethers per hectare plot from 8 d after anthesis (5 November 1990) until 165 days after anthesis (11 April 1991).

Results and discussion

Treatment with glyphosate suppressed stem and ear growth in the grasses. When grazing commenced, pasture treated with glyphosate yielded approximately 8.5 t DM/ha, whereas the control (unsprayed) pasture yielded about 12.5 t DM/ha. Glyphosate application delayed loss of soluble carbohydrates and crude protein from stems and to a lesser extent from leaf sheaths, but not from leaf blades. This delayed the decrease in the in vitro dry matter digestibility of the sprayed pasture relative to the control pasture.

Sheep grazing the senescing control pasture appeared to graze the developing grass ears in preference to other plant parts, but were only able to maintain their liveweight until approximately 60 days after anthesis. Thereafter, these sheep lost weight at about 115 g/head/day. Wethers grazing the treated pasture appeared to graze this material less selectively, and gained liveweight at 40 g/head/day until 60 days after anthesis, but thereafter also began to lose weight (approximately 115 g/head/day). The liveweight advantage (3 kg/head) gained by grazing the treated pasture was maintained until 124 days from anthesis. After this time sheep on the treated pasture lost weight more rapidly than those grazing the control pasture.

Glyphosate applied at the correct time will delay loss of feeding value in a senescing annual grass pasture and will allow improved animal performance. However, loss of feeding value cannot be delayed indefinitely and utilization of the treated fodder needs to be managed to maximise benefits.


Allden, W.G. 1959. Aust. J. Agric. Res. 10, 219-236.

Armstrong, R.D., Simpson, R.J. and Pearce, G.R. .1990. Proc. Aust. Soc. Anim. Prod. 18, 448.

Ballard, R.A., Simpson, R.J. and Pearce, G.R. 1990. Aust. J. Agric. Res. 41, 719-731.

Donald, C.M. and Allden, W.G. 1959. Aust. J. Agric. Res. 10, 199-218.

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