Issue link: https://read.dmtmag.com/i/466321
www.goodfruit.com GOOD FRUIT GROWER MARCH 1, 2015 7 strategies of assessing and responding to freeze damage during the Northwest Cherry Institute meeting held mid-January in Yakima, Washington. Additional meet- ings have been held this winter in Oregon to further discuss action plans. Assessing damage The main message to cherry growers impacted by the November freeze, or other cold events that may have happened this winter is: —Look at the whole tree (buds, spurs, and wood) to assess damage. —Adjust pruning accordingly. —Be prepared for indirect pest problems of bacterial canker and shothole borer. Cold damage can lead to secondary pest issues that are often as severe if not more so than the tree damage itself. Cold winters and spring frosts promote bacterial canker disease and make damaged trees susceptible to the shothole borer, a bark beetle. Lynn Long, OSU extension educator for Wasco County, saw 60 to 90 percent live buds in his first assessment after the freeze in OSU's Cemetery Block, which is home to more than 60 varieties and rootstocks. "But when I went back and assessed about 100 spurs per variety, I found significant spur damage," he said. Long categorized his spur assessments on a 1 to 5 level, with 5 representing heavy, severe damage. Several varieties fell in level 3, but many were in levels 4 and 5. Most of the wood damage occurred in one-year-old trees, an age that is most vulnerable to cold damage. Gip Redman, stone fruit grower in Wapato, Washington, and fieldman for the grower cooperative Oregon Cherry Growers in The Dalles, reported that he saw some damage in stone fruit trees in Washington's Yakima Valley, though not at the level of Oregon. Redman encouraged growers, especially those with orchards in low spots that had temperatures in the single digits, to assess potential damage by cutting buds and spurs before pruning. He also warned of the potential for small fruit this season from uneven bloom and the need to avoid overcropping trees. "I'm afraid growers will leave the treetops too full and not prune enough," he said, adding that light is needed throughout the tree to help regrowth. "In young orchards, you may need to cut the structure way back." He also recommends leaving blocks of young trees until last when pruning. "And don't cancel your bee orders yet. You still need to be ordering bees even if you are in Oregon." %H\RQG½RZHUV Dr. Todd Einhorn found about 50 percent bud kill at temperatures of around 6°F in laboratory cold hardiness studies conducted right before the November freeze. His findings confirmed what Long and other growers saw initially. Einhorn, tree fruit physiologist at OSU's Mid- Columbia Agricultural Research and Extension Center in Hood River, is working to develop a more predictive way of dealing with freeze damage in the future and will be combining cold damage analysis with spring growth data. "It's not always flowers that tell the whole story," he said during the Cherry Institute discussion. "The prob- lem is when you have 50 percent live buds and all this vascular tissue that's dead. Flowers can't make it without connective tissue." When the cambium is damaged, the tree cannot heal itself or repair spurs, he said, explaining that cells are compartmentalized and have unique functions. "You need the cambium to divide cells that form phloem and xylem. Cambium needs signals from the shoots and leaves pushing in the spring to activate it." Xylem is the water transport component of the tree, and phloem is the sugar transport. Phloem cells are gen- erally produced later and are not as likely to be injured as xylem cells. "So if you cut a section of spur and see black cambium, that's not a good sign for supporting flower growth," said Einhorn. "Flowers have to create vascular connections to the tissue or you will have flower drop and abscission." Grower shock The Dalles cherry grower Mike Omeg was shocked with the amount of spur damage he had. "I went from thinking that I had three-quarters of a normal crop to seeing 90 percent of spurs dead on Regina, 50 percent spurs dead on Bing, and a third of spurs dead on Skeena." He originally cut 7,000 buds and analyzed them for bud damage. Hearing of others experiencing spur dam- age, he then cut thousands more spurs from every block. It's been challenging to find good information on how to respond. "An event like this hasn't happened for a generation," Omeg said. "The freeze of 1955 was under a different scenario—orchards consisted of massive Bing and Royal Ann trees on Mazzard rootstock that had spurs 12 years old, pickers used tall ladders to reach fruit, and cherries were dryland farmed without irrigation." Today, trees are a tenth the size on dwarfing root- stocks, a multitude of varieties are grown, and trees are irrigated. "What will happen this spring to fruit buds if the spurs are damaged?" he asked. "That's the million-dollar question." Omeg said he is taking a cautious approach at Omeg Orchards because he doesn't know if flowers on dam- aged spurs will be viable. (See "Cold damage strategies") He is pruning less, not taking off as much wood as nor- mal. However, he is trying to cut out dead spurs because he doesn't want a zone of blind wood void of fruiting wood. • COLD DAMAGE STRATEGIES M ike Omeg won't know for sure how much the cold temperatures of last November and December will affect his 2015 cherry crop until later this season. Nonetheless, he's changed his pruning strategy and tightened his farm budget in preparation for what is likely to be a light crop. Omeg, cherry grower from The Dalles, Oregon, shared his orchard management strategy for the coming season: —Pull your head out of the sand. Assess all blocks thoroughly and rigorously so you know what you have to work with. —Develop a plan. This is not the year to farm by default or autopilot. Determine what crop yield thresh- old you need to still have enough fruit to make it worth picking and sufficient to attract pickers. "Washington will probably have a mostly full crop, which means that prices will not be extraordinarily high. Crop prices in The Dalles will probably be average, so you need to figure if you can afford to pick a two-ton crop." —Reduce pruning. Omeg is concerned that if he prunes too much of the crop off, he won't have cash flow and will be unable to attract labor in the future. He is methodically pruning block by block, considering each block individually. —Be conservative with operating costs and cut back where you can. —Be reactive. Watch your trees carefully this season and be flexible. "What do your trees look like 30 days after bloom? That's when they'll tell us what kind of crop we'll have this year." —Be prepared for all-out war against secondary prob- lems of bacterial canker and shothole borer. Although some orchards in Hood River and The Dalles have shown bacterial canker resistance to copper fungicide sprays, Omeg knows from previous isolated studies that his orchard is not resistant to coppers. He plans to aggressively spray copper during dormant and prebloom periods. —M. Hansen For more information about cold damage strategies, controlling bacterial canker and shothole borer, see "Fruit growers seek strategies for November freeze damage" at goodfruit.com.