Powdery Mildew (fungus - Podosphaera leucotricha): Young foliage shows cupping and twisting. The leaves are covered with a white, powdery mass of spores. Net russetting will occur on fruit when it is infected with this fungus. All varieties are susceptible, yet Jonathan appears to be more susceptible than most. Use of a regular fungicide program will control this problem. Karathane, a commonly recommended fungicide, should not be used at temperatures of 90 degrees F or above. A spreader should be used to improve control.

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