Good Fruit Grower

May 15

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Page 30 of 63 Good Fruit Grower MAY 15, 2016 31 (Colladonus geminatus) and the cherry leafhopper (Fieberiella florii) were capable of transferring WX from infected cherry to healthy peach trees. The success of WX transmissions was based solely on symptoms expressed in recipient plants that had become infected through feeding by leafhoppers with WX. Since the 1960s, little attention has been paid to the role of leafhoppers in the transmission of WX in Washington cherries. In California, where Western X disease is more prev- alent, many studies on leafhoppers transmitting WX have been accomplished. California's WX disease model involves two kinds of leafhoppers: the mountain leafhopper (Colladonus montanus) and the cherry leafhopper. The mountain leafhopper overwinters on winter annual weeds near waterways, and in early springtime, moves on to orchard floor weeds. While the mountain leafhopper is very abun- dant in California cherry orchards, it does not reproduce on cherries, preferring instead to inhabit orchard floor weed hosts, flying up occasionally to feed on cherry leaves. The mountain leafhopper is believed to introduce WX phytoplasma from wild plant hosts into a cherry orchard. The cherry leafhopper, which does reproduce on cherry, is known to pick up the phytoplasma from an infected tree and carry it to another tree nearby. Last summer and fall, Dr. Dan Villamor, research associate with the CPCNW, and I monitored leafhopper activity in cherry orchards in Yakima, Benton, Grant, Douglas and Chelan counties. Dr. Andrea Bixby-Brosi, research associate at WSU's Tree Fruit Research and Extension Center, moni- tored leafhopper abundance at three sites in Chelan County as well. Considering only those that potentially vector WX, the most abundant species found statewide were Colladonus reductus (no common name) and Colladonus geminatus, the geminate leafhopper. C. reductus is con- sidered a candidate WX vector as it bears a close resemblance to the mountain leafhopper. No mountain leafhopper was found in any Washington orchard. In late September, a population of cherry leafhoppers was found in one organic orchard in Chelan County. We found one cherry leafhopper in late October in a conventional cherry block in Yakima County; no other conventional orchard had this species. Molecular diagnostic testing was accomplished on leafhopper samples from 2015. DNA was extracted from either a single specimen or a pooled sample of several specimens. Using PCR (poly- merase chain reaction), we probed these leafhopper samples for a short piece of a gene that is very specific to Western X phytoplasma. We found many samples positive for WX from three potential vector species: the geminate leafhopper, the cherry leafhopper, and C. reductus. However, finding leafhoppers positive for WX does not label them as vectors; transmission experiments demonstrating that a leafhopper can pick up WX from a donor plant and introduce it into a recip- ient plant need to be done for proof. We received grant funds from the Washington Tree Fruit Research Commission to continue this work. Beginning this spring, we will monitor leafhopper traffic with yellow sticky cards placed in the orchard and in the habitat adjacent to the orchard (typically sageland). Orchard floor vege- tation will be sampled using sweep nets. In addition, we will assess the potential of certain plant species to serve as hosts for WX and/or leafhoppers. Transmission exper- iments will be conducted to verify the vector potential of certain leafhoppers. Targeting all leafhoppers with insecticide sprays when only one or two species are culprits is not economically justified. By updating and expanding our knowledge of the roles that leafhoppers play in the transmission of Western X disease, we can begin to move toward a sus- tainable, more targeted approach to leafhopper manage- ment in cherries. • Dr. Holly Ferguson is a research associate with Clean Plant Center Northwest at Washington State University's Prosser research station in Prosser, Washington. IF YOU SHARE OUR COMMITMENT TO QUALITY RELATIONSHIPS AND CUSTOMER AND CONSUMER SATISFACTION, PLEASE CONTACT ONE OF OUR PARTNERS TO LEARN MORE ABOUT GROWING WITH US. | 151 Low Road • Yakima, WA 98908 | 509.966.1814

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