Podosphaera leucotricha (Ell. & Ev.) Salmon
Powdery mildew is a problem on pears in the warm, irrigated valleys of Washington and Oregon and in some valleys of California. The disease has been reported as seriously affecting pears of the Flemish, Bartlett, Anjou, and Idaho varieties in Washington and Oregon. It is known to occur sometimes on quinces.
Powdery mildew attacks pear fruits more commonly than the foliage or twigs. It produces blackened areas, which become hard and may eventually crack open. On pears if is most serious when they are interplanted with susceptible varieties of apples (see Apples, Powdery Mildew).
For control follow the recommendations of the State agricultural extension service or experiment station.
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