THE EFFECT OF CERCOSPORA BETICOLA ( LEAF SPOT ) AN ' D DISEASE CONTROL MEASURES ON SUGAR BEET IN NATAL

The results of the first year of a three year feasibility study on the growing of sugar beet in Natal showed that Cercospora beticola is likely to be the most serious agronomic problem. In the second season of this study, the disease control measures of planting date, varietal resistance and fungicide application were investigated at two sites. The one was in the cooler (1 450 m in altitude) and the other in the warmer (950 m in altitude) region of the prospective sugar beet area. Leaf spot infection at the low altitude site at Baynesfield was markedly greater than at Nottingham Road. This was ascribed to the longer and more frequent daily periods of high humidity and temperature at Baynesfield than at Nottingham Road, particularly in December and January. The best drilling date was early in spring since this allowed a large proportion of the crop's growth to take place before its defoliation which occurred in February. Varieties Cremona, Kawerita and Kawecercopoly resisted infection for a while but were eventually defoliated by leaf spot in the same way as the susceptible varieties. A combination of fungicide treatment and varietal tolerance gave the highest sucrose yields (12 tlha) at Nottingham Road. The same treatment at Baynesfield failed to control the disease which eventually resulted in total crop loss.