Which statement best describes the host range risk among common grape varieties for powdery mildew?

• A. Pinot and Riesling prone; Chardonnay and Cabernet not
• B. Chardonnay and Riesling prone; Pinot and Cabernet not
• C. Chardonnay and Cabernet prone; Pinot and Riesling not
• D. Chardonnay and Pinot prone; Cabernet and Riesling not

Answer: (C)

Powdery mildew host range risk is about how likely a grape variety is to be infected, based on inherent susceptibility and how its growth habit creates a microclimate around the fruit and leaves. Varieties with denser canopies and leafiness near the fruit often provide conditions that favor the mildew’s spores, while other varieties may present less favorable conditions.

In many common teaching materials, Chardonnay and Cabernet Sauvignon are described as having higher susceptibility, so they’re viewed as more prone to powdery mildew. Pinot Noir and Riesling are considered less prone in the same context, making the statement that Chardonnay and Cabernet are prone while Pinot and Riesling are not the best fit for describing relative risk among these varieties. The other options mix up which varieties are regarded as more or less susceptible, so they don’t align as well with the typical guidance.