The Susceptibility of Varieties to Mosaic and the Effect of Planting Date on Mosaic Incidence in South Africa

The majority of South African sugarcane varieties are resistant to mosaic but two widely grown varieties, NCo 376 and.NCo 293, are highdy susceptible. Application of Temik (aldicarb) to the soil at planting was not beneficial in controlling mosaic. Mosaic transmission was restricted to January to May but very rapid spread only occurred in mid January to March, i.e. late summer and early autumn. The susceptibility of sugarcane to infection varied considerably with plant development. Young plants of NCo 376 of approximately 6-12 weeks were much more susceptible than older plants. Plants of' NCo 376 more than 16-20 weeks old were not severely infected, although very rapid spread occurred concurrently in younger plants. Differences of only 3 5 weeks in planting date exerted a marked effect on subsequent mosaic incidence. Planting susceptible varieties in early spring, thus avoiding the coincidence of a young, susceptible stage of growth with maximum vector activity in late summer and aur.umn, may cnable crops to escape severe outbreaks of mosaic.