Good Fruit Grower

April 1

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22 APRIL 1, 2015 GOOD FRUIT GROWER Research suggests Washington red wine grapes could benefit from new irrigation regimes. by Melissa Hansen T iming is everything when applying regulated deficit irrigation in red wine grape vineyards in Washington State. New research shows the importance of the timing of plant water stress and suggests that growers could apply even less water than current industry deficit irrigation standards without negative effects. In the last 25 years, regulated deficit irrigation (RDI) has become the norm for most wine grape varieties grown in eastern Washington. Much of the early research on RDI by Washington State University focused on white varieties. RDI is a controlled seasonal water deficit strategy that applies less water than the vineyard evaporates or needs, says Dr. Markus Keller, WSU horticulturist who specializes in grapevine physiology. When used properly, it allows growers to limit shoot growth, develop a more open and less dense canopy, and results in small berries and lower yields, improving fruit quality. In white varieties, berry size is not as important and there can be too much expo- sure of the fruit to sunlight, thus, WSU is revisiting the RDI approach for whites. Fine tuning grape irrigation COURTESY MARKUS KELLER iButtons, as shown in the bottom portion of this cluster, were used to record temperatures of sun-exposed and shaded grape clusters in the 25 percent ET and 100 percent ET strategies. Temperatures up to 120°F were recorded in the sun-exposed clusters in the 25 ET treatment compared to around 100°F on the same day in the 100 percent ET vines. Grape Irrigation

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