Effect of Ratoon Stunting Disease on the Yield and Components of Yield of Sugarcane under Rainfed Conditions

In a field trial conducted with eight varieties in the north coast area of Natal ratoon stunting disease (RSD) caused increasing lossesin yieldsof cane and sucrosefrom the plant to the second ratoon crop. All the varieties suffered losses in yield but the degree of loss differed markedly among the varieties. The total yield of sugar from the three crops was reduced by 38% in varieties NCo 376and N13, by between 19 and 26% in N12, J59/3 and N531216, by 11 to 12% in N52/219 and NIl and by 4% in N55/805. In the first and second ratoon crops of NCo 376 and N13 the loss in yield of sucrosewas more than 45%. The disease had little effect on cane quality and stalk population, and losses in yield werealmost entirelydue to decreases in stalk mass. Rainfall during the period of the trial amounted to 104% of the long term mean.