John Thull, Vineyard Manager
Matt Clark, Assistant Professor, Extension Specialist
Tracking the weather conditions at each vineyard site is something that growers should be doing over the winter months. Despite most of the grape varieties being ‘cold-hardy’, winter injury can come in many forms and cause damage. Winter injury can result from large shifts in temperature (more common in South Dakota), low temperature injury, repeated low temperature injury, bare soils, wind damage, and late spring frosts. Not only are vines impacted, but winter conditions also have a role in insect population life cycles.
The snow that most of the state received this past weekend (12/10-12/11) is well timed to provide insulation for the roots and bases of the vines. However, most of the vine is still above the snow-line and therefore these parts (trunks, cordons, canes) will be exposed to the low temperatures coming during the next couple of months. A pending polar vortex this week is predicted with lows in the negative single digits (Fahrenheit), something most cold-hardy hybrids should be able to endure if they had sufficiently acclimated for winter by responding to the shorter days and cooler temperatures.
How much cold a vine can endure depends on the state or condition of that vine going into winter. Stresses and environmental conditions from that growing season (rainfall amounts, growing degree days, solar radiation intensity, crop load, etc.) vary from year to year. Therefore, the cold temperature minimum that a vine can tolerate before suffering little cold injury will naturally change every season as well. For example, some years Frontenac can see -30°F with little or no damage and other times we may see Frontenac getting damaged already in the -20's range.
Without snow cover, the roots of the vines may see some damage, especially on newly planted vines, which can lead to symptoms of stunted growth and/or nutrient deficiencies in the next season. With a delivery of snow, the temperature drop below zero for a few days should have less of an impact. However, this may also favor Japanese beetle grubs which will also benefit from the insulation effects of the snow.
Monitoring the weather and vine health throughout the winter may seem like a chore, but it can help to set the vineyard manager up for success for the coming spring. For example, monitoring bud survival through the winter can inform pruning in the spring. Weather monitoring (all season long) is one of the best tools for understanding the yearly variation and to help in predicting insects, diseases, and also injury during the dormant season. Keeping these events in mind will help growers understand why their vineyards behave as they do during the upcoming growing season.