Powdery mildew affects all green parts of the vine, is favored by densely shaded canopies and overcast weather, and can reduce yields if infection occurs before flowering.

Powdery mildew affects all green parts of the vine, is favored by densely shaded canopies and overcast weather, and can reduce yields if infection occurs before flowering.

• A. Powdery mildew affects only the grapes and increases berry size.
• B. Powdery mildew affects all green parts of the vine, preferring densely shaded canopies and overcast weather, and can reduce yields if infection occurs before flowering.
• C. Powdery mildew enhances photosynthesis.
• D. Powdery mildew only affects roots.

Answer: (B)

Powdery mildew is a foliar and shoot fungal disease of grapevines that thrives on all green plant tissue and can spread quickly when canopies are dense. Dense canopies create a warm, humid microclimate with limited air movement, which favors the growth and spread of the fungus, and overcast conditions help by keeping leaf surfaces from drying out. If infection happens before flowering, it can impair inflorescence development and fruit set, leading to reduced yields. This combination—treatment of all green parts, preference for shaded, humid microclimates, and potential yield loss from early infection—best captures the disease’s biology and impact. The other statements are inaccurate because powdery mildew does not restrict itself to the grapes, does not increase berry size, does not enhance photosynthesis, and does not only affect roots.

Powdery mildew is a foliar and shoot fungal disease of grapevines that thrives on all green plant tissue and can spread quickly when canopies are dense. Dense canopies create a warm, humid microclimate with limited air movement, which favors the growth and spread of the fungus, and overcast conditions help by keeping leaf surfaces from drying out. If infection happens before flowering, it can impair inflorescence development and fruit set, leading to reduced yields. This combination—treatment of all green parts, preference for shaded, humid microclimates, and potential yield loss from early infection—best captures the disease’s biology and impact. The other statements are inaccurate because powdery mildew does not restrict itself to the grapes, does not increase berry size, does not enhance photosynthesis, and does not only affect roots.