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IRRIGATION BASICS FOR EASTERN WASHINGTON VINEYARDS By Michelle Moyer, Viticulture Extension Specialist, Department of Horticulture, Washington State University. R. Troy Peters, Irrigation Extension Specialist, Department of Biological Systems Engineering, Washington State University Irrigated Agriculture Research and Extension Center, Prosser, WA. Rick Hamman, Viticulturist, Hogue Ranches, Prosser, WA EM061E EM061E | Page 1 | ext.wsu.edu WSU EXTENSION | IRRIGATION BASICS FOR EASTERN WASHINGTON VINEYARDS Irrigation Basics for Eastern Washington Vineyards Introduction many of them are light-sensitive. If water stress is severe enough to reduce plant metabolic processes in the ripening For crop production, water is everything. Although water is berry, there may also be an associated reduction in the critical to plant growth and survival, water sources and control develop­ment of aromatic compounds. over them can vary substan­tially across the production regions of the world. For grapes, many regions in New World Juice grapes (Vitis x labruscana ‘Concord’ and ‘Niag•ara’) are production areas would not be so successful without irrigation better adapted to the typically high annual precipitation of and the control over grape growth and productivity it has eastern North America (30 to 50+ inches). Irrigation strategies provided. Irrigation has significantly changed the way grapes for juice grapes reflect this evolutionary difference and are are grown and managed in large-scale production systems by designed to opti­mize sugar accumulation and encourage high allowing grape production to expand into arid regions and by yields. improving control of plant nutrient status, water status, and frost and disease management. Grape producers in General Irrigation Strategies in Washing­ton State commonly use irrigation for either juice or Grape Production wine grapes. However, the various irrigation op­tions available can often appear contradictory, or are poorly explained in Understanding the way vines use water is paramount to terms of practical application. understanding irrigation strategies. During dif­ferent stages of vine development, water is needed for different physiological This Washington State University Extension publica­tion processes. These water requirements can be manipulated to presents and further clarifies irrigation options and strategies control vegeta­tive and reproductive growth of the vine. Since for both juice and wine grape produc­tion in Washington State. these plants have adapted to water stress, mild water stress can Companion pocket manu­als that supplement this publication actually help the plant become more efficient in its use of include the USDA-NRCS Program Aid 1619: Estimating Soil water. It does this because stress increases abscisic acid Mois­ture by Feel and Appearance, and the National Center (ABA), a plant hormone that is com­monly produced as a for Appropriate Technology: Water Management: The Pacific response to environmental stressors, and in this case, is Northwest Irrigator’s Pocket Guide. Both manuals are produced in the roots as a result of dry soil. The ABA is available upon request through Washington State University’s transported through the plant xylem (water-conducting vessels) Irrigation Extension website at http://ir­rigation.wsu.edu. to the shoots of the plant, signaling the leaves to close their stomata (tiny pores on the undersides of leaves that facilitate Irrigation Strategies for Wine and the intake of carbon dioxide (CO2) and export of water and Juice Grapes oxygen). ABA can inhibit shoot growth and may also inhibit other hormonal activ­ity. Unfortunately, one consequence of this reaction to water stress is that while the closing of stomata Wine grapes (Vitis vinifera) adapt well to water stress because prevents water loss, it also reduces the intake of CO2. This their roots can effectively search out mois­ture. In general, reduction in CO2 intake reduces photosynthesis and when supplied with enough or excess water, all grape varieties subsequent carbon assimilation (production of carbohydrates preferentially grow vegetatively (e.g., shoots). for immediate use and storage) in the plant. Irrigation strategies for wine grapes in arid grape-growing Budbreak to bloom. At the beginning of the growing season, regions are designed to optimize fruit quali­ty, influence water uptake by the plant roots is required to hydrate young potential wine style, and control canopy vigor. For example, buds and aid in an even budbreak. Water is also essential for many components of wine aroma come from the production of the uptake of soil-available nutrients. Thus, early-season isoprenoid compounds (e.g., monoterpenoids). These fertilization will be inef­fective, unless it is applied with aromatics are typically produced late in the berry-ripening appropriate levels of plant-available water. period. Some are produced in the skin of the grape berry, others in the flesh of the berry. Consequently, changes in berry Between budbreak and bloom, the vine is undergo­ing many volume (size) may alter the ratios of these particular developmental changes that are sensitive to plant water levels. compounds, which can be productive or counterpro­ductive, Shoots are growing rapidly, and the development of a fully depending on wine-style goals. Alterations in canopy functional canopy that maximizes sunlight absorption is development, and thus, canopy microcli­mate and fruit critical (Figure 1A). This rapid growth also requires substantial exposure, can also alter the produc­tion of these compounds, as nutrient uptake from the soil, which is achieved through EM061E | Page 2 | ext.wsu.edu WSU EXTENSION | IRRIGATION BASICS FOR EASTERN WASHINGTON VINEYARDS Véraison to harvest. After véraison, berries become Root Development in the Early Growing Season unresponsive to vine and soil water levels. They no longer predominately import water through the xylem (typically the Root growth typically starts around budbreak, but is most water-conducting vessels of the vascular tissue), but rather, active at bloom and will continue as long as there is import water and carbohy­drates through the phloem (the water and adequate soil temperatures (50°F or higher). A sugar-conducting ves­sels of the vascular tissue). Phloem tends well-developed root system is critical to long-term to be more resistant than xylem to changes in vine water levels grapevine health. Grape­vines can also selectively grow (Keller 2010). A common concern during this period is that roots in the search for water, which increases their ability additional water will result in berry splitting or dilution of to survive drought stress. For example, vineyards with flavors or sugars. Typically, this only occurs with heavy drip irrigation systems are most likely to have a major­ity watering after prolonged, relatively severe water stress, or as a of the vine root mass concentrated below the drip result of water on berry surfaces (due to precipitation or emitters, whereas roots in non-irrigated vineyards overhead irrigation). typically have root systems that extend beyond this zone (horizontally and vertically) as they search for water. In addition, the vine is beginning the process of slowing growth in preparation for winter dormancy. Excessive water and nitrogen during this period stimulates vine development nu­trient solubility in water. When flowers are actively and can impede this acclimation process. Mild water stress, by forming pollen, adequate water is critical to reduc­ing the inhibiting shoot growth, can aid in “shutting down” the vines development of sterility. Cell division is also occurring in the in preparation for winter dormancy. inflorescence anthers and ovaries. Thus, water stress at this time can reduce nutrient availability to developing tissues, Harvest through dormancy. As vines move into dor­mancy, induce pollen ste­rility, and reduce the number of potential they finish their final cycle of returning nu­trients to storage cells in the resulting berry, and potentially reducing final berry organs and are showing increased signs of acclimating for size. winter. While the plant is not actively growing aboveground during this time, water is still critical because there can be a Bloom to véraison. Between bloom and véraison, the second flush of root development. Over the dormant period, grapevine canopy can continue to grow, and in some cases, can adequate winter soil moisture is also critical because it helps cause excessive shading of the clusters (Figure 2). This is also protect a plant from cold damage to its roots (the water acts as a time when overwintering compound buds are being formed. an insulator). From a production standpoint, these late-season These buds house the following year’s clusters (inflorescence water applications prior to irrigation shut-off may be the only primordia) or tendrils (tendril primordia). The buds exposure moisture read­ily available for the upcoming spring to sunlight and warmer temperatures favor the devel­opment of development and budbreak (i.e., the period prior to the inflorescence primordia, while cooler temperatures and restarting of seasonal irrigation or the start of spring rains). shading favor the development of tendril primordia. In addition, the degree of branch­ing within a forming primordial is regulated by hor­mone interactions, which can be negatively affected by the over-production of ABA. In wine grapes, deficit irrigation is practiced during this time to maintain a canopy size that is adequate

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