Issue link: https://read.dmtmag.com/i/635697
www.goodfruit.com Good Fruit Grower FEBRUARY 15, 2016 19 Three pathogens are associated with little cherry dis- ease: little cherry virus strain 1, little cherry virus strain 2 and Western X. Infected trees produce small, poorly colored cherries that lack sugar and have a bitter fl avor. Determining how and when growers can reasonably predict a percentage of positive trees that show no symptoms from the disease is part of the focus of a research project that also involves entomologist Dr. Elizabeth Beers, virologist Dr. Ken Eastwell, agricultural economist Dr. Karina Gallardo, and extension specialist Tim Smith. The team sampled 250 trees in four orchards — some randomly and some within a one- to three-tree radius of a previously identifi ed positive tree — to determine which were positive for the disease. Field representatives then walked through the orchards to mark the trees they thought were positive and negative based on size, color and taste of the cherries. The goal was twofold: to see if infected trees could be easily identifi ed and to determine if more education is needed for workers in the orchard. The researchers also surveyed for mealybugs in the orchards to determine if their presence is an indicator for the disease, but none had any mealybugs. "So, mealybug can be a red fl ag, but it doesn't mean an infected orchard has to have an active mealybug population," Bixby-Brosi said. She shared results of the research from two of the four orchards. —Orchard 1: Tests confi rmed little cherry virus 2 in 2010 or 2011, with additional cases identifi ed from 2013 to 2015. During a walk-through last year, at least three of 10 fi eld workers fl agged all the positive trees. However, 85 negative trees were tagged as "suspect positive" by at least one worker — though Bixby-Brosi noted the walk- through occurred early in the season, when workers might not yet be adept at recognizing symptoms. All but fi ve of the positive trees were located within a one- to two-tree radius of a tree that was known to be positive in the past. None of the randomly selected trees tested positive for the disease. —Orchard 2: Tests confi rmed both little cherry virus strain 2 and Western X. Researchers sent six fi eld workers through the fi eld. Of the seven trees positive for little cherry virus strain 2, only three were fl agged by at least one fi eld worker, and four trees were not fl agged by any- one. The trees did not have any symptoms, but all were located within a three-tree radius of either a positive or suspect-positive tree. Four suspect trees tested positive for Western X. None of the randomly selected trees had the disease. Overall, the researchers found that most of the addi- tionally infected trees were located within a three-tree radius of previously positive trees and that random sam- pling is not an effective sampling method, Bixby-Brosi said. She recommended that growers ensure the root system of an infected tree is dead when removing it, because suckers from the root system also test positive for the disease. "For whole orchards, we don't have a rec- ommendation yet, but we've been hearing from growers who've been replanting that fumigation alone may not be enough, because some of that root system is still alive in the orchard." The research continues this year. • Differing life cycles pose challenges for controlling little cherry virus 2 vectors I n the past, mealybugs haven't posed a signifi cant problem for cherry growers because they don't cause direct damage to cherries, but because apple and grape mealybugs are vectors for little cherry virus 2, researchers are looking for ways to combat them. Control is challenging because mealybugs differ in their life cycles: The apple mealybug has just one generation per year, while the grape mealybug has at least two, which is an important consideration when timing control methods, said Dr. Andrea Bixby-Brosi, postdoctoral research assistant with Washington State University's Tree Fruit Research and Extension Center. With grape mealybugs, she said, "At some point in the summer, you could have eggs, nymphs, crawlers and adults on the same tree." Bixby-Brosi and a team of researchers tracked the life cycle of apple mealybugs at WSU's Sunrise Orchard between Wenatchee and Quincy in 2014 and 2015. They found that females were emerging from overwintering sites in midspring, followed by males. Egg masses were laid around June, and crawlers emerged during that month. "It's interesting to see the difference between 2014 and 2015," Bixby-Brosi said. "We had a hot spring and summer in 2015, and everything emerged about a month ahead of what it did the year before. That's another thing to take into con- sideration when managing these pests." The researchers tested several approaches to controlling the mealybugs: delayed dormant pesticide applications to intercept overwintering females; systemic petal fall applications to target crawlers; and foliar summer sprays timed when 70 percent of the crawlers are estimated to have emerged. In the 2014 trial, a combination of Lorsban (chlorpyrifos) and oil spray was found to be most effective at the delayed-dormant stage. Diazinon worked best at controlling the newly hatched crawlers later in the summer. Researchers tested again in 2015 and found the same results, with one addition: A combination of Centaur (buprofezin) and oil also was effective at the delayed-dormant stage. For grape mealybugs, systemic compounds, Admire Pro (imidacloprid, a soil drench) and Ultor (spirotetramat) and oil, applied 14 days after petal fall showed the best results. Research continues this year into possible chemical-control recommendation for organic growers, as well as research into natural mealybug enemies in orchards. —S. Dininny "Year after year, growers think they have it under control, and then the following year, there's more infection." —Andrea Bixby-Brosi PLAY Andrea Bixby-Brosi updates growers about little cherry virus research. Watch the video at bit.ly/littlecherryupdate Frost control has become very important to us. In the last 9 years, we have had 5 frost events that have signifi cantly damaged our production. We decided to do something to help mitigate this so our production would be consistent. That's where Orchard-Rite ® wind machines have come into play for us. 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