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p r a c t i c a l w i n e r y & v i n e ya r d J U ly 2 0 1 4 59 g r a p e g r o w i n g flow rate. 8 Gas exchange parameters are widely used in research. However, due to the cost of instruments and high require- ment of technical support, it may not be suitable for commercial production. 20 Measurements of sap flow rate can be automated; 14 however, the same draw- backs apply to this parameter. • Canopy temperature: Leaf temperature tends to increase when plants are drought- stressed due to stomatal closure. 20 Based on this, thermal-sensing techniques have been developed to evaluate plant water stress. 21 Due to its advantages in automa- tion and application in large scale, ther- mal sensing has the potential to direct irrigation in a way that accounts for spa- tial variability in the water requirement of large vineyard blocks. 2 Overall, measurements of vine water sta- tus offer direct assessment of the growth or physiological responses of vines under various levels of water availability. How- ever, most of these vine-based measure- ments require extensive technical support. Another potential difficulty of using vine water status to aid irrigation is that the calculation of amounts of irrigation is not as straight forward as soil-based approach. Thresholds that "trigger" irri- gation need to be established beforehand. One possibility is to well-irrigate small portions of the vineyard as control, which could provide dynamic thresholds reflecting the current seasonal condi- tions. However, the additional cost to manage a vineyard differently needs to be considered. These above-mentioned approaches have their pros and cons (Table I). Conse- quently, it is suggested to adapt at least two different approaches to direct irriga- tion. Good record keeping is essential, and long-term data are valuable, especially in calibrating based on local conditions. In practice, cost of instruments and labor could be a limiting factor. If that is the case, a good representation (enough replicates of repeated measurements) of fewer parame- ters is more useful than spotty measure- ments of many parameters. Deficit irrigation techniques Deficit irrigation is applying less water to the soil than what has been consumed as ET c , and consequently imposing water stress to the plants. In general, fast-growing tissues (shoot tips, flowers and pre-véraison berries) are more sensitive to water stress. Therefore, depending on the phenological stage, mild to moderate water stress can be uti- lized to manipulate growth with the goal to enhance berry quality. Severe water stress (i.e., stem < -1.5 MPa (-217 psi)), 9,16 should be avoided at all times. Two well- established deficit irrigation techniques are introduced below. When applying regulated deficit irriga- tion (RDI), period(s) of deficit irrigation and thus water stress are targeted at a specific phenological stage, and the soil/ vine water status is maintained accurately within a prescribed range. 22 For instance, it is common in red wine production to apply RDI after fruit set until véraison and to maintain stem between -0.5 and -1.0 MPa. 11 Therefore, routine assessments of soil/vine water status are necessary to avoid over- or under-application of irrigation beyond the prescribed range. With RDI, roots sense the decrease in v and soil , and trigger a series of physi- ological changes in grapevines such as production of the "stress hormone" abscisic acid (ABA), decreased g s and vine , and decreased tissue expansion. 10 In general, RDI can efficiently control both shoot growth and berry size, which is especially beneficial in red wine produc- tion. Water stress should be removed after the RDI period by filling up the soil water profile. Otherwise, vines could experience One BirdGardSuper PRO Wireless can control birds in up to 48 acres The Bird Gard SuperPRO Controller/transmitter can broad- cast distress calls to receivers up to 1000 ft in all directions. One Con- troller/transmitter can control up to eight 4-Speaker Wireless Receivers. No need to buy 8 complete Bird Gard SuperPROs. Each 4-Speaker Wireless Receiver protects up to 6 acres. Buy 2, 3, 4, up to eight 4-Speaker Wireless Receivers to protect up to 48 acres. You not only get wireless speakers, but also the distress calls randomly jump from speaker to speaker keeping the birds from getting used to the sounds. A limited special price for one BirdGard SuperPRO Controller/transmitter & one 4 Speaker Wireless Receiver is $799 (List $1050). Each additional 4-Speaker Wireless Receiver which covers up to 6 acres is $399 (list:$520). More and more vineyard managers are replacing netting with the Bird Gard PRO series. "Last year we got the SuperPRO Wireless. Had the starling flocks been there, we would have lost $20,000-$30,000 worth of grapes," Manager, Hazlitt 1852 Vineyards BirdGard Wireless JWB Marketing LLC 800.555.9634 For more discounts on the Bird Gard go to : birddamage.com