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X-Disease Phytoplasma Vector Management Field Days

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(North) East Wenatchee Oct 4th 2021

(South) Prosser Oct 8th 2021

Written by Corina Serban, WSU- Tree Fruit Extension ITT. Little Cherry Disease Program. November, 2021

For Spanish version click here


Tobin Northfield – Assistant Professor of Entomology; WSU Tree Fruit Research and Extension Center, Wenatchee

Host plant feeding and oviposition by leafhoppers (and the role of groundcover); Extenday/Surround field trials; DVAC demonstration for how to collect large amounts of insects quickly:

  • Feeding trials and molecular gut content analysis repeatedly show the importance of ground cover for leafhoppers
  • In the last two years Extenday applied postharvest has reduced leafhoppers by 81-91% compared to controls, despite wide variation in the control blocks across our replicates
  • Kaolin clay reduced leafhopper numbers in high pressure blocks by 47-48%, but not in very low-pressure blocks
  • Use of a DVAC is effective at collecting large amounts of adult and nymph leafhoppers for research

Louis (Louie) Nottingham – Research Assistant Professor; WSU Tree Fruit Research and Extension Center, Wenatchee

Insecticide trials findings:

  • Fourteen insecticides have been screened for efficacy against Colladonus reductus leafhoppers over the past two years.
  • Conventional insecticides resulting in 100% mortality (or very close) via direct spray contact include: 1. Actara (thiamethoxam), 2. Asana (esfenvalerate), 3. Admire pro (imidacloprid), and 4. Malathion 5EC (malathion).
  • Organic insecticides resulting in resulting in 100% mortality (or very close) via direct spray contact include: 1. Pyganic (pyrethrins), and 2. Azera (pyrethrins + azadirachtin.
  • Actara (thiamethoxam) was the only material that provided high efficacy via residues on leaves past 24 after application.
  • The particle films Celite (diatomaceous earth) and Surround (kaolin clay) significantly repelled leafhoppers from feeding on cherry leaves in greenhouse trials.

Tianna DuPont – Tree Fruit Extension Regional Specialist (North); WSU Tree Fruit Research and Extension Center, Wenatchee

Tree removal BMP’s (Best Management Practice) for X-disease:

  • Timely tree removal is key to slow the spread of Little cherry and X-disease. The pathogens can not be cured. In orchards where growers have removed infected trees promptly tree removal can be limited to a few trees per year, in blocks where growers wait whole block removal may be necessary.
  • Basic tree removal recommendations include: Scout and mark suspect trees. Sample trees if X-disease/ Little cherry disease is NOT confirmed in block or symptoms are not clear. Remove symptomatic/positive trees. Treat insect vectors before removal. Use glyphosate herbicide applied via cut stump/ notch or sample 1 tree out from symptomatic trees when removing individual trees. Remove adjacent trees with herbicide injury/positive results. If more than 20% positive consider removing entire block.
  • Fallow for at LEAST 1 year before replanting a block removed due to Little cherry.
  • Four tree removal trials conducted in 2019/2020 provided some additional information about herbicide use for tree removal: Herbicide applications resulted in injury of adjoining trees in Mazzard rootstocks but not smaller Gisela 12 and so herbicide applications may be most important on large (Mazzard) type rootstocks. May, July and Aug treatments resulted in root death but September did not. Apply herbicides when trees are actively growing. Frill applications performed best across trials but cut stump were only slightly less effective.
  • New grant funding is available for tree removal http://treefruit.wsu.edu/cost-share-for-little-cherry-and-x-disease-tree-removal/

Bernardita Sallato – Tree Fruit Extension Regional Specialist (South); WSU Irrigated Agriculture Research and Extension Center, Prosser

Update on replanting project:

  • In the initial prospection of LCD trees prior to installing the netting, three out of the six sites had one out of ten randomly sampled trees positive to X-phytoplasma. Age of these infected trees vary between one- and two-year-old.
  • Herbicide application over stump cuts during does not ensure complete root death, which vary between orchard rootstock, age, and if the removal was done on individual trees or entire block.
  • Live and infected roots where found the following spring after tree removal, in all sites that had individual tree removals.
  • Despite the presence of live roots positive to phytoplasma X, all ten replanted trees reported to be negative to LChV1, LChV2 and X-phytoplasma in August 2021.
  • In all 5 orchards where entire blocks were removed, no roots were found live, nor root suckers, regardless of the tree removal method, fumigation rate or timing, or rootstock (G12, Mazzard, K5).

 

Contact

Corina Serban
Tree Fruit Extension
Information Technology Transfer
Little Cherry Disease Program
Yakima Extension
corina.serban@wsu.edu

 

Washington State University