We are walking on pins and needles in the vineyards right now. Recent warm weather combined with a relatively warm winter are causing buds on some early budding varieties to swell. If we achieve bud break in late March, we will lose leaves and buds if we get a hard frost in April or even in early May. And, killing frosts are still a part of normal April weather patterns in Southeast Iowa.
Grapevines bud out apically. That is, they bud first at the end of each cane and subsequent buds open sequentially back towards the trunk of the vine. Also, pruning seems to stimulate bud break on vines. We will start pruning those varieties that are normally late in bud break so if we get a late frost, we are less likely to have leaf tissue exposed to cold weather. We will wait to prune early budding varieties, so if we get bud break early, the first buds will be out on wood that we plan to prune anyway.
Our big tasks this week are first to get our lime-sulfur sprays on all vines, and secondly, to prune our Edelweiss because it is traditionally a vine that buds out late each year. We are using the pruning of the Edelweiss to train our new vineyard staff on pruning and also to develop our skills in using our V-Mech mechanized pruning system.
Finally, one indicator of just how close buds are to breaking is the amount of sap that flows when we prune. Last week, we pruned some Frontenac as a training exercise and every time we cut last year’s growth off, the sap flowed. This is an indication that the ground and roots of the plant are warm enough to start opening buds within the next few days.