Effects of Mycosphaerella Leaf Spot on Growth of Eucalyptus nitens. J. E. Lundquist, Research Officer, Plant Protection Research Institute, South African Forestry Research Institute, D. R. de Wet Forestry Research Centre, Sabie, South Africa. R. C. Purnell, Research Officer, South African Forestry Research Institute, D. R. de Wet Forestry Research Centre, Sabie, South Africa. Plant Dis. 71:1025-1029. Accepted for publication 4 April 1987. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/PD-71-1025.

Standard disease assessment diagrams for estimating the severity of Mycosphaerella leaf spot, caused by Mycosphaerella nubilosa, were developed based on percentage of spotted leaf area and degree of defoliation. The diagrams were used to evaluate disease severity in 11 provenances of Eucalyptus nitens growing in Eastern Transvaal, South Africa. Variation in disease severity was found among and within provenances. Provenances from New South Wales, Australia, were more resistant than those from Victoria. Growth rate was negatively correlated with disease severity but was not affected until 25% of the crown was defoliated.