What is a key management approach for grey rot?

• A. Selecting grape varieties with large grapes and thin skins
• B. Keeping a very dense, closed canopy
• C. Traditional sulfur and copper sprays are always effective
• D. Antagonistic bacteria such as Bacillus subtilis

Answer: (D)

Grey rot is Botrytis cinerea, a fungus that thrives in humid, still conditions and on grape surfaces. A key way to manage it is through antagonistic bacteria such as Bacillus subtilis. These beneficial microbes live on the grape surface, compete with Botrytis for nutrients and space, and can produce antifungal compounds that help suppress the pathogen. Using a biocontrol agent like Bacillus subtilis fits well with sustainable viticulture and can be used alongside other practices to reduce Botrytis pressure.

Why the other ideas aren’t as effective: selecting grape varieties with large berries and thin skins would actually increase susceptibility to Botrytis rather than control it. Maintaining a very dense, closed canopy creates a humid microclimate that promotes the fungus. Traditional sulfur and copper sprays can help, but they’re not always effective against Botrytis, especially in wet conditions or when resistance or coverage limits efficiency.