Answer: Some plants are more prone to powdery mildew than others, and the disease can strike plants that are under stress from too little sunshine, poor air circulation or just generally not thriving. Depending upon the vine, you may be able to spray with a fungicide to protect the unaffected leaves and stems, but fungicides won't help the plant parts already diseased. Sometimes the best approach is to prune out the affected plant parts. This not only removes the pathogen from the garden, it opens the plant up to better air circulation and sunlight penetration. You can try both approaches to rid your vine of mildew.
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