Issue link: http://read.dmtmag.com/i/459886
14 FEBRUARY 15, 2015 GOOD FRUIT GROWER www.goodfruit.com Call us FIRST for the largest selection of trees and rootstocks available Future contracts for cherries, pears, & apples; ALL ROOTSTOCKS. NEW APPLE rootstock! 1-800-421-4001 Phone: 503-538-2131 Fax: 503-538-7616 E-mail: info@treeconnect.com Web: www.treeconnect.com INC. Representing Over 30 Leading Nurseries in the U.S. and Europe From the breeders of Bud 9: • Vigor between M-9 T337 and M-9 Pajam®2 • Yield efficiency similar to M-9 T337 • Dwarfing • Cold hardy • Disease resistant • Fireblight tolerant B10 ® cv. Mich 96 USPP 21,223 Services are FREE TO GROWERS! Disease control is even more important these days with the opening of new foreign markets. Susceptibility In some crops, the fruit's resistance to powdery mil- dew increases as they age during the growing season. "Most fruit crops, like babies, are most susceptible to powdery mildew in the early stages of fruit develop- ment," she said. Infants are initially at high risk for dis- eases, but develop immunities as they get older to ward off diseases. But not so with sweet cherries. In fact, Probst says the reverse happens. In crops like grapes and hops, research has shown that fruit and flowers are most susceptible early in the season. Because of that, growers concentrate fungicide sprays during this vulnerable, hypersensitive time near bloom, but they can back off spraying later in the season, although sprays for foliage infection are often needed. "Surprisingly, cherries are most resistant to powdery mildew early on and lose their resistance as fruit develop, becoming least resistant near maturity at harvest," she said. To study fruit susceptibility, experiments were con- ducted in an orchard of Bing and Sweetheart cherries that had a history of powdery mildew. Researchers used specially made bags from nylon mesh material used in aquaculture. The material is fine enough to prevent pow- dery mildew spores (conidia) from moving in or out. The bags allowed researchers to inoculate fruit with a known amount of conidia and track disease development throughout the season. From the onset of fruit set, fruit from five treatments in the study were covered with the bags. In each treatment, half the fruit were inoculated with conidia and immedi- ately covered and the other half remained uncovered for two weeks to allow disease exposure to occur naturally. After either inoculation or exposure for two weeks, fruit of that treatment were covered for the remainder of the study. The timeline started at 24 days after full bloom, because that's when disease was first observed in the orchard, and concluded around 90 days post bloom, which was near harvest. At the end of the trial, each treatment had been exposed naturally for a different two-week period, which allowed Probst to control and assess the timing of fruit infection. Fruit needed to be exposed naturally as well as by inoculation so she could compare overall disease inci- dence in the orchard at the end of the study. She found