Further evidence of the effects of ratoon stunting disease on production under irrigated and rainfed conditions

In a field experiment under rainfed conditions, reductions in cane yield over three crops due to infection by ratoon stunting disease (RSD) ranged from 41% to 19% respectively in varieties N17, N14, N21, NCo376 and N19. Losses in N12 were 10%, and in N23 and N22 were 7% and 1%. In a similar trial conducted under irrigation, the greatest reductions in cane yield over two crops were 32% in variety N25, 29% in NCo376, 22% in N24 and 21% in N19. The effects of RSD on yield of recoverable sucrose were similar to those on cane yields. Reductions in yield were mainly due to reductions in stalk mass. Based on field experiments conducted since 1980 to determine the effect of RSD on growth and yield, currently popular and new South African released varieties are ranked as follows in terms of the effect of RSD on production: intolerant, N17, N14, NCo376, N24, N25; intermediate, N24, N19, N13, N23; relatively tolerant, N22. That substantial losses from RSD can occur in most varieties under irrigated as well as rainfed conditions demonstrates the importance of precautionary action by growers to prevent the introduction and spread of RSD in cane plantings.