BULLETIN OF THE 
C2) USDEPARTENT OF AICTE a 
No. 120 
Contribution from the Bureau of Plant Industry, Wm. A. Taylor, Chief. 
September 3, 1914, 
APPLE POWDERY MILDEW AND ITS CONTROL IN 
THE PAJARO VALLEY.’ 
By W. S. BALLARD, Pathologist, Fruit-Disease Investigations, and W. H. VoLck, 
County Horticultural Commissioner of Santa Cruz County, Cal? 
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 leucotricha (KE. and E.) 
‘Salm., and P. oxyacanthae 
(DC) de Bary.’ 
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, Fic. 1.—Map of the United States, the shaded area 
; showing where apple powdery mildew occurs oc- 
and Japan. In the cen- 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 
1This 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. 
2These 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. : 
~%See also page 5. x 
 46689°—Bull. 120—14-—_1 
