. Bulletin of the Department of Agriculture. Agriculture; Agriculture. APPLE POWDERY MILDEW AND ITS CONTROL IN THE PAJARO By W. S. Ballard, Pathologist, Fruit-Disease Investigations, and W. H. Volck, County Horticultural Commissioner of Santa Cruz County, Cat? INTRODUCTION. Apple powdery mildew is a fungous disease which attacks the foliage and young twig growth of the apple. Occasionally it occurs on pears, more particularly on nursery stock in damp or foggy locali- ties, and at times it seriously injures quinces. The disease is quite widely distributed over the world and may be
. Bulletin of the Department of Agriculture. Agriculture; Agriculture. APPLE POWDERY MILDEW AND ITS CONTROL IN THE PAJARO By W. S. Ballard, Pathologist, Fruit-Disease Investigations, and W. H. Volck, County Horticultural Commissioner of Santa Cruz County, Cat? INTRODUCTION. Apple powdery mildew is a fungous disease which attacks the foliage and young twig growth of the apple. Occasionally it occurs on pears, more particularly on nursery stock in damp or foggy locali- ties, and at times it seriously injures quinces. The disease is quite widely distributed over the world and may be caused by either of two very similar fungi, namely, Podosphaera leucotrieha (E. and E.) Salm., and P. oxyacanthae (DC) de Powdery mildew of the apple occurs at least occa- sionally in nearly all parts of the United States and is reported from some Prov- inces of Canada. It is widely distributed in Eu- rope and occurs also in Australia, New Zealand, Fig. 1.—Map of the United States, the shaded area and Japan. In the Cen- lowing where apple powdery mildew occurs oc- 1 _ casionally and the black spots where serious out- tral and eastern United breaks are common. States it has been known for many years as a more or less serious disease of nursery stock, but it is only during the last few years that it has been reported as doing any considerable damage in bearing orchards. In the western United States, however, from 1 This bulletin is intended to assist apple growers in dealing with a fungous disease which is becoming a serious menace to their industry. It is suitable for distribution in the apple-growing sections west of the Rocky Mountains and in certain limited areas east of the Rocky Mountains, as shown on the map. 2 These investigations were carried on cooperatively between the Office of Fruit- Disease Investigations of the Bureau of Plant Industry and the office of the county horticultural commissioner of Santa Cruz County, located at Watsonville, Cal. 3 See also pag
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