Late Spring Frost Damage

frost damage 3b

Frost damage was spotty and tough to find in this Conneaut vineyard.

Let’s face it: We all knew it was a possibility when forecasters predicted frosts for the days after Mother’s Day. Temperatures that dip below 28°F can be damaging to tender green grape tissues. Of course, that all depends on how long the temperature stays at the critical lows. At just about an hour, green grape tissues (leaves, shoots, clusters) can be damaged as the water in the cells turns to ice, expands, and breaks the cell walls. Once those cell walls are broken and the contents of the cells’ guts leak out, water-soaking can be seen in leaves, shoots, and clusters within hours after a freezing event in the spring. What we had this past Tuesday morning was low temperatures ranging from 28°F to 31°F, so there was some damage, but it was not at all extensive in most vineyards.

critical temperature.preview

This image comes from Iowa State University’s IPM page. At each progressive stage, the tissues become more sensitive to cold temperatures to which buds were once tolerant.

Where there was frost damage in the Ashtabula area, it was spotty and not much of a concern. That’s why when we grow grapes in cool climates, we are sure to leave up extra buds to make sure that enough of a crop can survive past the frost/freeze danger zone in springtime. Think you’ll need 60 buds/vine to get a decent crop off your Noiret? Try leaving up 10% more to ensure that there will be enough that will survive spring freezes. It’s easy enough to go back through the vineyard to do some shoot thinning at about 5″ shoot growth.

frost damage 2b

The brown or black tissue results from the plant cells freezing – the ice expands and breaks the cell walls, which then leak cell “guts” all over. The loss of the cell structure and chlorophyll result in this necrosis, or browning of tissues.

No one likes to say it’s safe to say we’re past the frost danger zone, but we all like to hope – no matter how secretly. So, I hope everyone emerged this week relatively unscathed and that Tuesday morning was the last of the cold temperatures in the area this spring.

-JCG

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