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76 p r a c t i c a l w i n e r y & v i n e ya r d M ay 2 0 1 4 T E C H N I C A L R E S O U R C E F O R G R O W E R S & W I N E R I E S 78 Mount Eden Vineyards expands with Silicon Valley Bank loan By Cynthia Bournellis 85 Role of trace metals in wine 'reduction' By Marlize Viviers, Mark Smith, Eric Wilkes, Paul Smith and Dan Johnson practicalwinerylibrary.com Access Practical Winery & Vineyard article archives online. C alifornia has not seen a drought year like 2014 in recent history. Many vineyards not only have a limited water supply for irriga- tion, but the water in their root zone is well below the full water-holding capac- ity. With our rainfall future uncertain, we need to prepare for the worst. Here are four drought-management strategies for your consideration. The first strategy is artificial rain. Flood, furrow or sprinkler irrigation arti- ficially refills root zone moisture. This recharging ought to occur about three or four weeks prior to bud break to ensure roots emerge from dormancy normally, leading to normal bud break, shoot emer- gence and early season shoot growth. After that, schedule irrigations as in any other year. The artificial rain strategy assumes a supply of water sufficient for both root zone recharge and normal irrigations through the growing season. This assumption, along with the surface irri- gation system requirement, is prohibitive for many vineyards. All three of the next drought-manage- ment strategies need the following water- conservation methods for success. First, diligent control of weeds in the vine row to eliminate water loss through their tran- spiration. Second, disk and ring-roll the tractor rows to remove transpiring vegeta- tion and to make a barrier of loose soil that limits evaporation. Third, thin shoots early (≈ 3 to 6 inches long) and severely (less than six shoots per foot cordon) to reduce transpiration through vines. For the same reason, if canopies grow too large, hedge them to about 14 to 16 nodes per shoot after shoot growth stops. These strategies also warrant maxi- mum value from applied water. To that end, ensure the best possible drip irriga- tion system performance with regard to uniformity in pressure, flow and distri- bution. Also, promote the highest possi- ble infiltration rate into the soil through organic and mineral amendment addi- tions (Figure 1). The second drought-management strat- egy familiar to many wine grape growers is regulated deficit irrigation (RDI). The only difference for 2014 is that RDI sched- ules should have begun three or four weeks before bud break instead of between May and July. This early onset of drip irri- gation is necessary to accommodate the drought-induced soil-moisture deficit. Even with these early irrigations, the soil profile may only contain about 4% to 13% of the moisture that it could if fully recharged from rain. After initiating irri- gations, monitor vine moisture status, soil moisture status and evapotranspira- tion (ET) as you normally would, and irrigate accordingly. The longer RDI sea- son requires more irrigation water than in a normal year, but less than artificial rain due to greater irrigation efficiency and plant water use efficiency. Stan Grant, viticulturist BY Management strategies for drought conditions Figure 2: Extensive defoliation of Chardonnay. Photo source: ProgressiVe Viticulture© Photo source: ProgressiVe Viticulture© Figure 1: Wetted soil with unimpaired water infiltration. g r a p e g r o w i n g