Issue link: http://read.dmtmag.com/i/283151
www.goodfruit.com GOOD FRUIT GROWER APRIL 1, 2014 19 the wet side helps maintain the vine. It works best in deep, sandy loam soils, she said. The main disadvantage is that it requires separate drip irrigation lines on each side of the vine. Advantages are that partial root zone drying is more flex- ible in the timing of irrigation and more forgiving if irrigation is late compared to RDI. While growers must match their irri- gation strategies with their goals, Zhang believes there may be a place in Wash- ington for PRD, depending on variety and wine styles. For red cultivars like Cabernet Sau- vignon, Merlot, and Syrah, where small berries, deep color, and concentrated fla- vors are sought, RDI is beneficial. But for aromatic white varieties—Chardonnay, Riesling, and Sauvignon Blanc—less sun exposure is desired than in the reds and PRD may work better, she said. "Partial root zone drying can give good tonnage without sacrificing quality." Growers can use deficit irrigation in the vineyard to manipulate wine styles, she said, adding that growing a variety like Sauvignon Blanc in a dense canopy can result in more herbaceous characters, if that is the desired goal. Good and bad Deficit irrigation, when done properly, can improve grape quality, Zhang said. Deficit irrigation benefits include substantial savings in irrigation water, limiting unnecessary shoot growth, manipulating berry size, and modifying wine style in the vineyard. Having a more open canopy sets off a chain of positive events—better fruit exposure and air cir- culation in the fruit zone leads to reduced disease pressure and improved fruit quality. But bad things can happen if the vine is stressed at the wrong time or stressed too much. In early spring, insufficient water in the soil profile before bud break can result in poor and delayed bud break and stunted shoot growth. If winters are dry and bleeding sap is not observed in the vineyard when soil temperature has reached 50°F, it's a good indication that soils are dry and irrigation is needed. "Too much stress before fruit set can result in poor fruit set and even necrotic inflorescence," she said, adding that stress before veraison is the best time to influence berry size. "Too much stress at veraison can result in yellow leaves, early defoliation, and cause potassium to recy- cle from the leaves to berries and increase juice potassium and pH." Another critical time is after veraison as harvest nears. Too much stress after veraison and preharvest can dehydrate berries, result in sunburned grapes, and reduce yields, she noted. In the postharvest stage, the vine needs to harden off for winter. The can- opy should be healthy, but not vigorously growing. "Growers should refill the soil moisture for overwintering," she said. • F or more information on irrigation, ET, and crop coefficients, download the WSU bulletin Irrigation Basics for Eastern Washington Vineyards at http://cru.cahe.wsu.edu/ CEPublications/EM061E/EM061E.pdf. TOPGUARD ® Fungicide Specialty Crops Only the best for the best. Contact your local crop advisor or dealer or visit www.cheminova-us.com Plan. Protect. Profit. TOPGUARD Fungicide Specialty Crops protects against powdery mildew and rusts beTer than any fungicide in its class. Its powerful systemic acOvity rapidly protects sprayed fruit and foliage, including new growth, providing maximum protecOon. For apples, TOPGUARD Specialty Crops tank-mixed with KOVERALL® Fungicide provides enhanced control of scab. For cherry leaf spot control in cherries, mix TOPGUARD Specialty Crops with a protectant. TOPGUARD Specialty Crops is an essenOal component of an apple or cherry fungicide program that maximizes fruit quality and tree health. Always read and follow label direcOons. TOPGUARD and KOVERALL are registered trademarks of Cheminova, Inc. Yun Zhang of Washington State University says that grape growers can manipulate vine growth with deficit irrigation, but timing is critical to avoid severe water stress. PHOTO BY TJ MULLINAX