Residual effect of glyphosate as a ripener on sugarcane.

The effect of a low dosage of glyphosate in raising the juice purity and sucrose content of unstressed sugarcane 'stalks is well documented. The residual effect of the ripener on the succeeding crop of cane grown under favourable conditions has been shown to be short-lived, seldom influencing yields. The low residual activity of glyphosate was confirmed in several trials grown under optimum moisture conditions. In one large trial in which three successive crops were sprayed no evidence of a residual effect on yield was found. Yields were, however, increased considerably by the ripening effect of glyphosate. In three rainfed trials affected by drought, yields were reduced by 11 to 17% due to the application of glyphosate on the preceding crop. The decrease in yield in some varieties was much greater than in others. Varietal differences could be attributed to the different sensitivities of varieties to drought rather than to glyphosate per se. It is recommended that glyphosate be used only where cane is not stressed or likely to be stressed between the time of spraying and harvesting.