Association between Nutrients and Rust in Sugarcane in Kwazulu-natal

Brown (common) rust has recently been prevalent in the South African sugar industry, particularly on N29, a sugarcane variety that is often severely affected by the disease. Cool, moist conditions have favoured the development of rust, but there has been a tendency for more severe infections to be associated with well grown sugarcane. To investigate this observation, two parallel rows, one with higher rust levels than the other, were selected in a field of N29. Soil and leaf samples were taken at 3 m intervals along each row and analysed for nutrients, and the leaves were assessed for the severity of rust infection. The data were subjected to principle component analysis. The results indicated that rust strongly interfered with the physiology of the plant. The presence of rust appeared to favour the uptake of K, to the detriment of Ca, Mg and Si. It is hypothesised that early application of Ca, before rust infection, may reduce levels of infection by limiting the uptake of K. The results also suggested that the application of Si might offer some protection against the fungus. Nematodes did not influence rust severity.