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Grapevine Management Under Drought Conditions

Grapevine Management Under Drought Conditions

EM4831E
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Gwen-Alyn Hoheisel, Regional Extension Specialist, WSU Extension, Benton-Franklin Counties, Michelle Moyer, Statewide Viticulture Extension Specialist, Department of Horticulture, Washington State University Irrigated Agriculture Research and Extension Center
Under drought conditions, vineyards are impacted by a variety of environmental factors that growers may or may not be able to control. This publication discusses the many water-related factors that affect the health and productivity of grapevines in a year of low water availability. It gives specific suggestions, including cultural practices, irrigation strategies, and alternative water sources, and lists resources for growers to help manage their vineyards for optimum long-term health and productivity.
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The severity of impacts that drought conditions have on grapevines in a year of low water availability depends on a number of factors that are specific to individual vineyards. Some of the factors that influence a grower’s ability to manage severe water stress include:

  • Timing of water delivery
  • Amount of water available
  • Duration, intensity, and timing of hot spells
  • Soil texture
  • Soil depth
  • Method of irrigation

In newly planted vineyards, water management is critical for proper vine establishment. Without sufficient root growth, which is driven by the supply of adequate moisture, vines will struggle with establishment and winter survival. Under drought advisories, if water restrictions are substantial enough to prevent proper irrigation regimes, growers may consider delaying the establishment of new vineyards until irrigation forecasts have improved.

The information presented here, along with other advisories on irrigation management and efficiency, outline the management concerns and possible solutions for growers during periods of inadequate water availability for mature plantings.

Grapevine Water Use

Grapevines can adapt to both low and high water availability in the surrounding soil. Vitis labrusca ‘Concord’ is native to the eastern United States and is thus more suited to higher water availability. Wine grapes (Vitis vinifera) have evolved under drier conditions and are more efficient in their water use.

Regardless of plant origin, a basic volume of water is needed for vine survival; in order to reach optimum yield and crop quality, more water than the “absolute minimum” is needed. A general rule of thumb is that 12-16 acre-inches of water is the minimum amount required during the growing season to actually produce a viable crop. However, this rule is highly variable because it is affected by soil type, age of vine, weather, root depth, crop load, and other growing attributes. This effectively means that vines can survive droughts, depending on the severity and duration of the drought, but they may not produce fruit.

Effects of Water Stress

Extreme water stress in vines is most damaging when it occurs between the phenological stages of bloom to pea-size berries (late spring to early summer), concurrent with rapid shoot growth, ovule fertilization, and rapid cell division in young berries (Figure 1). Water stress during this time will result in poor berry set and small berries.

Figure 1. Berries at “fruit set.”
In Pacific Northwest wine grapes, regulated deficit irrigation (RDI) is usually practiced between the phenological stages of pea-size berries to véraison (July to mid-August), when cell expansion is occurring in the berry (Figure 2). However, severe water stress during this stage of berry development can dramatically reduce berry size and may delay or, under very severe conditions, prevent fruit maturation (Moyer et al. 2013). In some cases, the vines will also pull water from the developing fruit to maintain shoot health, resulting in premature berry dehydration (i.e., berry shrivel).

Between the stage of véraison and harvest, RDI is still a common practice in red wine grapes, but not white wine grapes or juice grapes.

At this time, vines are less susceptible to drought conditions because they begin using the phloem, rather than the xylem, for water transport. The phloem is less susceptible to changes in soil water levels (Keller 2010); however, they still need sufficient soil moisture so as not to go past the permanent wilting point of the plant. RDI during this time period aids in slowing vegetative vine growth, and helps the processes associated with vine dormancy and cold hardiness acclimation.

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Issued by Washington State University Extension and the U.S. Department of Agriculture in furtherance of the Acts of May 8 and June 30, 1914. Extension programs and policies are consistent with federal and state laws and regulations on nondiscrimination regarding race, sex, religion, age, color, creed, and national or ethnic origin; physical, mental, or sensory disability; marital status or sexual orientation; and status as a Vietnam-era or disabled veteran. Evidence of noncompliance may be reported through your local WSU Extension office. Trade names have been used to simplify information; no endorsement is intended.