Control of pests by manipulation of weeds in genetically modified herbicide-tolerant sugar beet
2000
Dewar, A.M. (Institute of Arable Crops Research Broom's Barn, Higham (United Kingdom))
An experiment was set up in 1998 to study the effect of glyphosate on the weeds and pests in glyphosate-tolerant sugar beet, in comparison with a conventional herbicide regime. Glyphosate (as Roundup Biactive) at 1.08kg a.i. per ha was first applied at the 2-4 leaf, 8-10 leaf and 12-14 leaf stage of the crop, followed by a second application at the same rate 2-4 weeks later. In untreated controls and the two later glyphosate treatments, weeds almost completely covered the ground in mid-June, at the time that aphids were migrating into the crop. The numbers of aphids (mostly Myzus persicae Sulzer) colonising beet were higher on plots treated with conventional herbicides and those treated with glyphosate at the 2-4 leaf stage than on untreated or plots treated later with glyphosate. Large numbers of the leaf curling plum aphid (Brachycaudus helichrysi Kaltenbach) colonised the weeds within untreated or later treated plots. These were accompanied by predators and parasites which eventually caused substantial mortality in those aphid populations, and perhaps also those on the sugar beet. Sugar yield was 5 percent greater in the early-sprayed glyphosate plots co-pared to the conventional, but yield losses caused by the late removal of weeds in the later-sprayed glyphosate plots were 24 and 31 percent respectively. The results suggest that the latest application of the first glyphosate spray in a 2 spray programme should be before the 8 leaf stage of the sugar beet to avoid weed competition reducing yield.
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