VIEW ARTICLE

Ecology and Epidemiology

The Spread of a Powdery Mildew of Peach. P. F. Kable, Principal research scientist, Department of Agriculture, Agricultural Research Centre, Yanco, New South Wales, 2703 Australia; P. M. Fried(2), and D. R. MacKenzie(3). (2)Plant pathologist, Swiss Federal Research Station for Agronomy, 8046 Zurich; (3)Associate professor, Department of Plant Pathology, The Pennsylvania State University, University Park 16802, USA. Phytopathology 70:601-604. Accepted for publication 19 November 1979. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-601.

In New South Wales, Australia, powdery mildew is found on peach fruits when roses are growing nearby. An Oidium sp. fungus spreads from roses in the spring, causing fruit blemishes. Only primary spread occurs. The percentages of peach fruits infected by the mildew fungus on trees at various distances from mildew-infected rose thickets were recorded in orchards at Leeton, New South Wales, and the relationship of disease frequency to distance from the source was examined by regression analysis for both the Gregory (Y = aD^–b) and Kiyosawa and Shiyomi (Y = ae^–bD) models of disease spread. The pattern of spread in all instances was better explained by the Gregory model. The relationship between disease incidence (Y) and distance (D) from the inoculum source was given as Y = 11,885D^–1.923 with a coefficient of determination (R²) of 97.9% for one orchard in 1974, Y = 763,836D^–3.401 (R² = 83.9%) for the same orchard in 1976, and Y = 106,170D^–3,00 (R² = 95.9%) for a second orchard in 1976. Isolation distance of the inoculum source to the orchard required to hold disease to ≤5% would be less than 60 m for all three epidemics.