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2000-12-01
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Mitchell, B.J., Weed control in glyphosate tolerant sugar beet, End of Project Report, Teagasc, 2000.
Abstract
Between 1997 and 1999 weed control trials were carried out with sugar beet
tolerant to glyphosate. Glyphosate was applied at a total dose of 1620.0, 2160.0,
3240.0 and 4320.0 g a.i. ha-1 in two and three applications. These were
compared with a standard and double standard three spray sugar beet herbicide
programme. In all seasons application of the lowest dose of glyphosate, 1620.0
g a.i. ha-1 gave marginally better control of weeds than the standard herbicide
programme. Herbicide timing was more flexible with glyphosate and only two
weeds, Polygonum convolvulus and Lamium purpureum required more than one
application to kill all the weeds. In most cases no significant difference in weed
control was observed between the glyphosate treatments after the second and
third applications but the three spray programmes were marginally better than
the two spray in 1997 and 1998. In 1997 the sugar beet strain was not totally
tolerant to glyphosate and a reduction in plant numbers was recorded after the initial glyphosate application. The strain used in subsequent years was fully
tolerant and no plant loss occurred even at the highest glyphosate dose. At
harvest most of the root yields in the glyphosate treatments were significantly
higher than the yields from the standard herbicide comparison treatments. Crop
vigour was not affected by any of the treatments in 1997 but in 1998 and 1999
the two standard herbicides reduced crop vigour by 10 and 20 per cent
respectively.