The same question seems to come up at the end of every January lately: Do you prune now or try to hold off longer? With the temperatures rising, the warming climate and many drought years in California the vines start showing some signs that they might be waking up. In that case, you want to prune soon before you get bud break. But if you prune too soon what if you get a real cold spell and what about the risk of Eutypa?
The frost risk comes from concern that pruning too soon will cause the vines to bud early, and with that comes the risk that a frost will hit and damage the buds. In northern California the risk is relatively low. There’s less than a 50% probability of frost in our area after Feb 9th according to the Farmer’s Almanac. With global climate change that risk is further reduced.
Eutypa lata is a fungus that can cause Eutypa dieback (also known as Dead Arm or grape canter), a disease caused by a deep seated wood rot that can occur after pruning. Wind dispersed spores can infect a pruning wound and cause trunk diseases. The risk of this is higher in December. If you are pruning in December the recommendation is to do double pruning where you leave 8 or more inches of cane in December, then go back and do a second and final pruning in February.
Overall, the risk of Eutypa tends to be higher in Cabernet Sauvignon than some other varieties. With a number of our vines beginning to push in late January a pruning isn’t a major concern especially if a wound pruning protectant is used.
For more info than you may care to know about trunk disease, check out these posts: