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Impact of Viruses on Cherry Fruit Size

Dan VillamorKen Eastwell

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�Physiological / Horticultural

�Winter damage to vascular system

�Mineral imbalance (Zn+2 deficiency)

�Pathogens

�Root or crown rots

�Virus-like agents**

Damage to vascular tissue contributes to small fruit:

Many of the VLA’s that lead to small fruit are found in the PNW

Cherry necrotic rusty mottle

Cherry rusty mottle

Cherry raspleaf

Cherry mottle leaf

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�Little cherry virus 1 (LChV1)

�Little cherry virus 2 (LChV2)

�Western X disease phytoplasma (WX)

Pathogens Number of positives per county Total(145)Chelan Yakima Grant Benton

LChV1 0 0 0 0 0

LChV2 38 23 0 10 71

WX 29 6 15 1 51

LChV1/LChV2 1 7 0 0 8

LChV1/WX 4 0 0 0 4

LChV2/WX 6 1 0 2 9

LChV1/LChV2/WX 2 0 0 0 2

(Beers, Villamor, Bixby-Brosi, Eastwell: funded by WTFRC)

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Little cherry virus 2:

� Family Closteroviridae

� Genus Ampelovirus

Little cherry virus 1:

� Family Closteroviridae

� Genus unassigned

Thread-like particles

Symptoms of Little cherry virus 2 :

�LChV2 infected fruit is small, late ripening and insipid

0

2

4

6

8

10

12

Yellow(-22 days)

Pink(-10 days)

Ripe(Harvest)

Fru

it w

eig

ht

(gm

)

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Symptoms:

‘Sweetheart’‘Lambert’

‘Canindex 1’ ‘Bing’

Premature autumn coloration is unreliable

in most cherry cultivars in most years

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(courtesy Landon Michaelson)

Three major factors:

1. Series of cool springs

2. Elevated insect vector populations

3. Heightened awareness of fruit size

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Little cherry virus 2 transmission:

�Apple mealybug:

�Reported in Wenatchee in 1997 (R. Miller)

�Grape mealybug:

�Populations increasing from Southwest

�Infestations becoming more prevalent because of shift to different chemistries.�No spray programs until 2012

�Not an economical pest in absence of virus

Mealybugs are difficult to manage:

� Crawlers dispersed long distances:� in wind� on debris� on farm equipment

�Overwinter in crevices, under bark

�Tree tops�Quickly out of

control

(E. Beers)

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Little cherry virus 1:

�Occurs in Washington State and British

Columbia

�Relatively low incidence throughout state

�Vector(s) unknown for Little cherry virus 1�Spreads more slowly than Little cherry virus 2

�Symptoms:

�Milder than those of Little cherry virus 2

�Together, symptoms are very severe

“Albino”

� Symptoms spread slowly through tree

� Reduced extension

� Fruit severely impacted� Bitter taste

Western X phytoplasma

• Specialized bacteria with no cell wall

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Western X disease

� X-disease of peaches prevalent mostly “in close proximity to virgin, sagebrush land.” (Coe 1942)

�First diagnosed in cherry in Washington in 1946

Western X phytoplasmatransmission:

�Mountain leafhopper (Colladonus montanus)� Overwinters on winter

annual weeds near water (clovers, dandelions, curly dock)

� Adults migrate to orchard weeds in late spring

� Most abundant in sweet cherry (only) but not preferred host and does not colonize

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Western X phytoplasma transmission:�Cherry leafhopper (Fieberiella florii)

�Feed on wide range of woody plants (sweet

cherry, bitter cherry, & choke cherry)

�Most important species for tree-to-tree spread

Cherry leafhopperCherry leafhopperCherry leafhopperCherry leafhopper

Management of Little cherry virus 2:

�Plant only virus-free trees (pollinators!!)

�Prompt removal and replanting

�Rogue symptomatic trees and replace

�Be wary of root grafting

�Remove entire orchard and replant

�Bitter cherry (Prunus emarginata) is a host

�Choke cherry (Prunus virginiana) is NOT a host

�Vector control

�Caution during tree removal

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Western X management:

�Remove diseased trees

�Most important source

�Treat with insecticide before removal

�Manage nearby ornamental hosts

�Includes chokecherry and bitter cherry

�Remove or treat with insecticide

�Control weeds that harbor leafhoppers and phytoplasma

�Treat orchard for leaf hopper vectors

�Delayed dormant oil sprays plus insect control until leaf drop

The correct control strategyis essential for success!!

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For more information:http://healthyplants.wsu.edu