We were out on the vineyard last night as temperatures reached as low as -4C. At this time of year frost is our biggest nightmare as it can cause significant damage even before bud burst. Michigan State University have produced a chart showing vine frost tolerance at different temperature levels according to bud development http://www.ristcanyonvineyards.com/grape_frost_tolerance.html
Our vines are mainly at the stage of full swell and some damage will occur at around -3C. With the help of the boujies, orchard burners, a FrostBuster and a converted corn dryer, we managed to keep most of the vineyard above -2.5C. However I recorded some areas at -3.5C so we will have to wait and see how much damage has been done.
No frost is forecast for the next few days but we still have some time to go before the risk of frost diminishes. Once the buds have burst -1C will cause around 10% damage but this could increase to 90% at -3C when there are three leaves on the vines.
No doubt some more sleepless nights ahead.