Following harvest, grapevines continue to take up carbohydrates and mineral nutrients needed to produce carbohydrate reserves in permanent wood structures used for respiration during dormancy and to fuel new growth the following season. Inadequate water after harvest and through the winter hinders this process and is thought to induce delayed spring growth. (DSG)
As described in the December 2013 issue of the Vine Lines, published by the Fresno County University of California Cooperative Extension office, poor winter rainfall can enhance DSG, especially when a post-harvest irrigation was not applied.
Symptoms of DSG include poor and uneven bud-break, stunted growth, smaller flower clusters or complete abortion of clusters, failure and death of individual buds and growth of suckers at the base or head of the vine.
DSG can affect entire vineyards. Many of the cases have involved Thompson Seedless vines. However, other varieties have also shown the erratic growth pattern of this condition.
Normally, after harvest, a traditional flood-irrigated raisin vineyard has gone two months without water. Wine grape vineyards, depending on variety and harvest date, may also go for long periods without being irrigated. Deciding when to irrigate a particular vineyard depends on many factors. But, soil type and vine vigor and /health are probably most important.
Sandy soils will be depleted of soil moisture much faster than finer textured soils. Also, vines may show symptoms of water stress as the fruit matures or raisins dry.
Vineyards planted to finer textured soils may not show stress. Often they don’t require growth and encourage cane maturity.
Among the factors to consider when making late-season irrigation decisions:
- Soil type and problems (sandy soils or those with soil pests)
- Trellis type and canopy size
- Rootstock type
- Vineyard age
- Pest pressure
- Time of last irrigation
- Climatic conditions post-harvest
The Extension newsletter strongly suggests a winter irrigation when rainfall is less than an inch during the months of November and December. Keep in mind that mature vineyards maintained on drip irrigation don’t suffer fluctuations between wet and dry soils. As a result, they can begin storing carbohydrates during harvest, reducing water stress. One- to three-year-old vineyards should be irrigated when winter rainfall is minimal, regardless of soil type.
Assuring that at least one-third of the soil profile is re-wetted by mid-December will also help minimize the effects of cold damage, the newsletter adds.