Oidium or powdery mildew of the vine . Fig. 3. Blackening of canes due to Oidium. OIDIUM OR POWDERY MILDEW OF THE VINE. 319 These marks, at first brown, later black, are usually branching orfern-like in form, showing the points of attack of the fungus. If thecanes are attacked when young, they fail to mature properly and oftenturn black over their whole surface. It is this form of Oidium whichhas sometimes been mistaken for Anthracnose in California. Later, the blossoms and fruit may be attacked. When the blossomsare attacked they fail to set, and if the berries are attacked when verysmall, th
Oidium or powdery mildew of the vine . Fig. 3. Blackening of canes due to Oidium. OIDIUM OR POWDERY MILDEW OF THE VINE. 319 These marks, at first brown, later black, are usually branching orfern-like in form, showing the points of attack of the fungus. If thecanes are attacked when young, they fail to mature properly and oftenturn black over their whole surface. It is this form of Oidium whichhas sometimes been mistaken for Anthracnose in California. Later, the blossoms and fruit may be attacked. When the blossomsare attacked they fail to set, and if the berries are attacked when verysmall, they will fail to develop and will drop off. If the fruit reachesnearly full size before being affected, it continues to develop, but irreg-ularly. The parts of the epidermis injured by the fungus become hard-ened and cease to grow. This results in irregularity in the form of theberry and in severe cases in cracking. (See fig. 4.).
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