Effect of nematodes on the sustained production of sugarcane in South Africa

An attempt is made to quantify the long-term benefit from the sustained production of sugarcane in South Africa using nematicides to reduce the damage caused by nematodes in each crop. The study was conducted using data from the plant crop and four or five ratoon crops from two trials located on similar sandy soils. Treatments comprised aldicarb and an untreated control, applied to a total of 10 sugarcane cultivars. Two cultivars were common to both sites. The plant parasitic nematode communities were similar at both sites except that Meloidogyne javanica was absent from one site. Yield of ratoon crops was correlated with the yield of the plant crop. Annual losses from nematodes were similar over successive crops. Data from both sites showed there to be a significant, positive correlation between yield of the nematicide treated plots and size of the response to treatment. Over a 4-year period, M. javanica alone was responsible for 30% of the losses, equivalent to 15 t cane/ha per year. The long-term effect of nematodes on sugarcane production was measured after calculating a logarithmic function from the observed yields of successive ratoons. Without a nematicide the time taken for the yield to decline to a threshold of 40 t cane/ha per year ranged from a minimum of 1 year in the M. javanica infested site to a maximum of 9 years in the other site. Treatment with a nematicide increased this period considerably. On the site with M. javanica it took a projected 20 years before the yield of one of the cultivars reached the threshold and 43 years for the same cultivar at the other site. The use of a nematicide increased long-term production, on average, by a factor of 3 at the M. javanica infested site and a factor of 5 at the other site. Differences between cultivars in the rate at which ratoon yields declined meant that, over time, the best cultivars at both sites were not the ones which gave the greatest annual yields during the first few crops after planting.