APRIL 2019 • COUNTRY LIFE IN BC


17


Sudden fruit tree dieback a growing concern Researchers trying to find out why


by TOM WALKER KELOWNA – The annual BC


Tree Fruit Horticultural Symposium took place in Kelowna on February 24. The usual format of guest speakers in the morning was followed by a choice of more intensive workshops in the afternoon. A number of orchards


across the valley have been hit by a what’s described as sudden apple decline (SAD). Afflicted apple trees


develop signs of stress during the growing season and die within three weeks. “The rapid death was


atypical of anything we have seen around the Okanagan, and up to 40% of the trees in some blocks are dying. This is a big deal,” Agriculture and Agri-Food Canada plant pathologist Daniel O’Gorman told a packed afternoon session. O’Gorman has based his


research into the phenomenon on work done in Ontario and New York. Cornell University has looked at possible contributing factors to SAD, including fire blight, herbicide damage, boring insects, winter damage, drought stress, fungal pathogens and viruses. Researchers haven’t


identified a single cause of the problem. O’Gorman suspects multiple causes exist. He has applied for research funding to investigate further. One of the likely


contributors to SAD is the fungal pathogen Cytospora. While active in apple orchards, it is typically a greater concern for stone fruit growers. “We haven’t tested the


fungi present on our apple trees to see if they are pathogenic, if they can cause disease and how virulent they are,” says O’Gorman. “So that is some of the work that has to be done,. Colorado State University plant pathologist Jane Stewart gave growers an overview of her research controlling Cytospora in peaches, including the effectiveness of painting pruning wounds. The wounds are known to be a primary access point for fungal pathogens. Plant pathologist Danielle


Hirkala provided an overview on Cytospora in the Okanagan. “Cytospora was first


identified in 1818, so it is not a new problem,” she notes. “But our growing practices are so much more intense than in the past.”


She advises growers to maintain tree vigour. “If you have healthy trees,


you are not going to have a problem. And remove all


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affected trees and wood at the first sign of disease. The fungus can live in the bark of a dead tree for up to six months,” she says. AAFC research scientist


Peter Toivonen reviewed his work investigating the causes of apple soft scald, a disease that affects apples in cold storage. “Soft scald is a chilling-


related injury,” he explains. “Most apples are tolerant of very low temperatures, but we find certain batches of both Ambrosia and Honeycrisp are susceptible when we put them into cold storage.” Toivonen has found that if the apples are under water stress in the field four or five weeks before harvest, some of the tissues in the apple will be weakened. “When you put those apples into cold storage, say at half a degree, they get a chilling injury,” he says. Toivonen emphasises that


water stress can be both too little or too much. He has traced soft scald in BC orchards that have been affected by late season drought conditions, while colleagues in Ontario and New Zealand have seen the same condition from too much water in the weeks before harvest. Lindsay Hainstock, a field


services staff person with BC Tree Fruits, gave an overview of a visit to New Zealand. She


BC Tree Fruits field services person Charlotte Leaming, left, presented the annual Golden Apple award to Pearl Beckett and Gary Schnierer who operate a 14-acre apple orchard in southeast Kelowna. Leaming noted the competition this year came down to the pack-outs from some difficult varieties. Beckett and Schnierer grow Ambrosia, Gala, Mac, Spartan and Honeycrisp. “Their grades ranged from 80% to 92% extra fancy depending on the cultivar and they hit that size sweet spot of 72 to 88,” noted Leaming. TOM WALKER PHOTO


showed examples of intensive trellis systems that apple growers are adopting to push the maximum number of apples per acre. The systems take advantage of New Zealand’s longer sunlight hours. Depending on the system, growers aim for 135 to 195 bins per acre. (Average Okanagan production ranges from 30 to 85 bins per acre.) “The important thing about


these trips is to listen very carefully about the growing conditions in their area because you can’t just take what they are doing and apply it to BC,” cautions Hainstock. “The situation here is not the same, but it is exciting to see growers really push the limits.” Afternoon workshops included a research news flash where Summerland Research


and Development Centre scientists gave five-minute talks about tree-fruit related research projects. BC Ministry of Agriculture pesticide specialist Ken Sapsford reviewed products growers will be losing and keeping over the coming year. Growers also heard about better sprayer calibration and best management practices for rodent control.


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