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Dear Dr. Vinny,

Can grapegrowers limit the effect of shatter?

—Robert D., France

Dear Robert,

Grape shatter (known as coulure in French) occurs when grape clusters don’t develop completely during their infancy. It’s mostly the result of Mother Nature: rain, wind, extreme temperatures. Shatter means a grapevine’s flowers either weren’t pollinated and never developed into berries, or the berries fell off soon after they were formed. What you end up with are bunches of grapes without a bunch of grapes—they instead have very few grapes.

Weather conditions aside, we know that some grape varieties are more at risk for shatter, including Grenache, Malbec and Merlot. There is conjecture that certain rootstock or clone selections might be more susceptible, too. Pruning too early or too severely might contribute to shatter, and particularly fertile soil (which might cause the grapevine to develop quickly, and before the cool, wet weather has passed) is thought to be another cause.

—Dr. Vinny

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