Issue link: http://winesandvines.uberflip.com/i/643683
March 2016 WINES&VINES 47 While nitrate moves readily to grapevine shoots, the nitrogen it contains cannot be used in the shoots. To be useful, it must be converted into organic forms. This conversion begins with nitrate being reduced to ammo- nium. An enzyme, nitrate reductase, facili- tates this process. Nitrate reductase requires cofactors to function, which leads us to three important interactions. The first involves Zinfandel. During ripen- ing, it is not uncommon to see Zinfandel vineyards with pale foliage in California's northern interior winegrowing region. Often, the foliage on these vines fails to darken fol- lowing calcium nitrate fertigation applica- tions through drip irrigation. Upon closer examination, some leaves in these vineyards display the mottled, creamy chlorosis of boron deficiency (center photo on page 46). Zinfan- del is prone to boron deficiency, which is a cofactor of nitrate reductase. When boron is deficient, nitrate is not converted and accu- mulates in foliar tissues. In these situations, boron fertilizer applications will correct the problem, stimulating nitrate conversion, dark- ening foliage and promoting ripening. Second, early in the growing season in the Sacramento River Delta, some vineyards have pale foliage that fails to darken after calcium nitrate applications. In these cases, there may be a few leaves on basal portions of shoots— typically on the shade side of canopies—with a somewhat pale interveinal chlorosis (bottom photo on page 46). These are the symptoms of mild manganese deficiency. Manganese is another nitrate reductase cofactor, and when it is limiting, manganese fertilizer applications by foliar spray or drip application will elicit foliage darkening and growth responses. Third, like boron and manganese, molybde- num is essential for nitrate conversion. During bloom, some varieties prone to poor fruit set respond to foliar-spray applied molybdenum fertilizers, even though there are no signs of deficiency. Such varieties include Merlot and Malbec. Without molybdenum applications, nitrate may accumulate to toxic levels in cluster tissues in these varieties, inducing yield-de- creasing flower abortion (see photo above). These are only a few examples of important mineral nutrient interactions. There are likely others whose importance we have not yet discerned. Should your vines not respond as expected to fertilizer applications, mineral interactions may be the cause. Stan Grant is a consultant working mainly with grape- growers and vineyards in the northern interior of Cali- fornia (Lodi, Delta and Sierra Foothills) and the eastern San Francisco Bay Area. 2016 marks the 16th anniver- sary of his consulting business, Progressive Viticulture. Previously, Grant was director of farming at Duarte Nursery and viticulturist with Gallo Vineyards. He earned a master of science degree in soil science from the University of California, Davis. For more information, visit progressivevit.com. This article is dedicated to the memory of University of California Cooperative Extension specialist emeritus Pete Christensen for his many contributions to grape- growing and the viticulture profession. PRACTICAL WINERY & VINEYARD GRAPEGROWING TTB LABEL APPROVALS Low per-label costs Gov't. Liaison Negotiations or Footwork Reasonable Hourly Rates TRADEMARK SEARCHES As Low as $185 Your trade names or designs are searched at the U.S. Patent Office to help establish valuable ownership or avoid costly legal liability. Over 100 years' total staff experience handling every government liaison need for industry. Phone or write for details. 200 N. Glebe Rd., Suite 321 Arlington, Virginia 22203 Phone: (703) 524-8200 Fax: 525-8451 TOLL-FREE 1-800-642-6564 Major Credit Cards Accepted www.trademarkinfo.com Since 1957 GovtLiaison_Dir08 11/29/07 2:00 PM Pag Toll-Free: 877-552-4828 909-464-1373 • Fax: 909-464-1603 For your nearest dealer, contact: BRANCHLOK™ Used for lateral training of trellised branches and cordons to 12-14 gauge wire. Branchlok™ is available in three lengths: 2½", 3¼", 3 ¾". Patent No. 4,665,000 WineVineBranchLokAD.qxp_Layout 1 12/1/14 2:46 Excessive flower abortion is evident in a fledgling grape cluster. A significant number of California vineyard soils developed from rocks that are comparatively rich in magnesium.