A Large-scale Diagnostic Service for Ratoon Stunting Disease of Sugarcane

The Experiment Station has provided a diagnostic service for ratoon stunting disease (RSD), based on microscopic observation of the causal bacterium, since 1977. The service is widely used by growers to determine the extent of RSD in commercial cane fields and sources of seedcane, and it is also frequently used by Extension staff for survey purposes. The procedures used for diagnosing RSD are outlined and the results are discussed on an area basis. From 1981 to 1983, samples from a mean of 4 169 fields were examined annually. Approximately 45% of the samples were from intended seedcane sources. The number of samples from commercial fields folind to contain RSD declined from 32% in 1979 to 21% in 1982 and 1983. For seedcane there was a decline from 25% to 12% over the same period. RSD is least common in the Lower South Coast, Midlands South and Umvoti extension areas in southern and inland Natal. The disease is most common in the warmer parts of the industry, ie the Pongola and NelspruitKomatipoort areas in the eastern Transvaal and in the Umfolozi area of northern Natal. In 1983, from 40 to 55% of commercial fields were contaminated in these three areas. Intensive efforts to control RSD are in progress in all parts of the industry.