Winter Protection of Grapevines
Winter Injury to Grapevines
Winter cold injury occurs after the vine has hardened and may affect buds, canes, trunks, and even roots. The primary bud is generally the first to die when exposed to cold temperature, followed by the secondary and tertiary buds. If most of the primary buds are damaged by winter injury but if a large percentage of the secondary buds survive then there may be still the potential for a moderate to normal crop (Zabadal et al., 2007). The tertiary buds although having negligible fruitfulness are very important for developing leaf area. Low temperature can kill canes and trunks too.
Assessing Winter Injury to Grapevines
The ability of a dormant grapevine to tolerate cold temperatures is referred to as its cold hardiness. Grapevine cold hardiness is a highly dynamic condition, influenced by environmental and growing conditions varying among grapevine varieties over time.
Bud Damage: For each variety in a suspect block, it is necessary to sample the percentage of primary bud survival. Making decisions for crop levels and overall vine health is best estimated from primary buds and this is best achieved by evaluating bud survival prior to pruning.
Cane and Trunk Damage: Cold injury to the vascular tissues of canes and trunks is more serious than bud injury to the longterm health of the vine.
Selection and Handling
The canes selected for bud evaluation are those that would normally be left for tying in the spring. Selection of 10 to 12 of these canes (no more than 1 cane per vine) is taken for the variety for assessment. Where there are obvious topographic differences or vine size differences additional samples can be taken to better represent the area.
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