Issue link: https://read.dmtmag.com/i/654468
www.goodfruit.com Good Fruit Grower MARCH 15, 2016 19 hinders the vine's ability to uptake water. Once it's damaged, it doesn't repair itself. Washington State University has developed a cold hardiness model to pre- dict grapevine cold hardiness anywhere temperature data is available. But each vineyard has its own climate and micro- climates, and growers should know as much about their vineyard as possible to make it easier to assess if cold damage is a concern when a cold front hits. Sampling for damage Gwen Hoheisel, WSU Extension educator in Prosser, Washington, and Matt Halldorson, viticulturist for Ste. Michelle Wine Estates, offered tips for assessing for cold damage during the Washington Association of Wine Grape Growers annual meeting in Kennewick, Washington, in February. Growers should consider the number of variables in their vineyards, such as variety, soil types, elevation changes, air- fl ow and cold spots (low-lying areas that would allow cold air to pool). "Learn your vineyard very well," Hoheisel said. "The more variables you have in your fi eld, the more samples that you need to take, but samples take time and effort." Growers also should identify a critical temperature at which point they suspect their vineyards might be susceptible to damage, then monitor the weather. "If you think you've crossed this threshold, if you've gotten close, it's worth assessing," Halldorson said. "If you haven't gotten close, don't bother. It's a lot of work." In collecting samples, Hoheisel said divide a vineyard into zones and sample randomly for 100 buds in each zone. Remember, she said: Structures, wind machines and wind breaks can alter the microclimate in a vineyard, so keep these things in mind when dividing a vineyard into zones. Making the cut Cut above the fi rst two to three buds if you are worried about losing spur posi- tions, but if possible sample the entire cane to ensure that you are looking at the most important node positions (the fi rst three). Look for patterns, by keeping track of where the buds fall on the cordon, and assess for variability. A grapevine's primary bud is most fruitful, but it is the least cold-hardy. The secondary bud is a little more cold-hardy but is less fruitful. The tertiary bud is the most cold-hardy but only tends to break unless there is damage to the other buds and is almost never fruitful. "Basically, your bud represents next year's crop, and it represents your money, so it's a pretty serious subject," Halldorson said. Gather canes and let them sit overnight (24 hours is best). If the canes look wet before 24 hours, you're seeing signs of cold damage. Focusing on basal buds, make a parallel cut to the cane. If you see a lot of woolly hairs protecting the bud, cut a little deeper to fi nd the primary bud. Make a vertical cut from the leaf scar to fi nd the secondary bud. The third cut is more downward to uncover the tertiary bud. Green is good; a black or brown colored bud is dead. Assessing canes is trickier, Halldorson said. It is easy to cut too deep into the phloem and miss the damage completely. In addition, the cambium and the phloem go all the way around the trunk; a grapevine could be green and healthy on one side, but brown and damaged on the other. "Cut the cane in half," he said. "We're dealing with a lot of tissue here that runs up and down, and it can be really challenging." A lot of phloem damage isn't the end of the world, because the phloem will generally repair itself, he said. As far as the xylem goes, growers should check the xylem in spring if they're seeing intense bud damage. "If you don't have really bad bud damage, chances are that your xylem is fi ne," he said. • ONLINE For more information about assessing for cold damage, as well as spreadsheets to guide you through the process, visit bit.ly/1WEJQYe ® Trademark of The Dow Chemical Company ("Dow") or an affiliated company of Dow Always read and follow label directions. www.dowagro.com Delegate ® Insecticide. Insecticide applications may target a single pest, but other pests are likely residing in your orchard. With Delegate, you can control multiple pests at once, including: n Codling moth n Thrips n Leafroller n Leafminer n Spotted wing Drosophila n Cherry fruit fly n Pear psylla Pests are controlled by contact and ingestion. And the translaminar movement (into the leaf) of Delegate helps reach pests out of the direct line of spray. To learn more, visit www.DelegateInsecticide.com. MULTIPLE PESTS LURK. COINCIDENTALLY, DELEGATE ® CONTROLS MULTIPLE PESTS.