little cherry disease - wsu tree...

World Class. Face to Face.

Detecting and Managing Little Cherry Disease

Organic Pest and Disease Management Fruit SchoolMarch 15, 2017

Andrea Bixby-Brosi and Elizabeth Beers: Entomology, Wenatchee, WAKen Eastwell and Dan Villamor: Plant pathology, Prosser, WA

Tim Smith: Regional Extension Specialist, Wenatchee, WA


Roadmap1. Introduction2. Insect vectors: apple mealybug (AMB), grape mealybug

(GMB), and leafhoppers.3. Insect control4. LCD identification/indicators 5. Sampling methods/strategies.6. Management strategies


Little Cherry Disease (LCD)

• Symptoms§ Produce cherries

of small size and poor color and flavor

• Results§ Economic losses§ Tree and orchard

removal

Bing Cherries

World Class. Face to Face.Aerial photos showing loss due to LCD2011

2013 2015


Another example of Loss due to LCD

20062009201120132015


LCD pathogens and vectors 1. Little cherry virus 2 (LChV2) (pathogen)

• Transmitted by • apple & grape mealybug (vectors)• Root grafting

2. Western X phytoplasma (WX) (pathogen)

• Transmitted by • various leafhopper species (vectors)• Root grafting• Surprising resurgence discovered in 2014

3. Little cherry virus 1 (LChV1) (pathogen)

• Mode of transmission unknown• Present at low level throughout WA State• Typically found in combination with LChV2 or WX

World Class. Face to Face.Phloem feeding/infection• Phloem § Responsible for transporting sugars throughout

the plant§ Underneath the outer bark

• Mealybug and leafhopper vectors§ Feed on phloem§ Piercing/sucking mouth parts


Vectors and Control


Mealybugs vector LChV2 and can be wind dispersed


Little Cherry Virus 2 transmissionApple mealybug (AMB) - Univoltine

Egg masses on apple

Egg mass

Crawlers on underside of leaf

Adults


Apple mealybug phenology

DelayedDormant

Systemic

Foliar Crawler


Apple mealybug control 2014

DelayedDormant

Systemic Petal Fall

Foliar Crawler


Apple mealybug control 2015

Foliar Crawler

Systemic Petal Fall

DelayedDormant

World Class. Face to Face.AMB parasitism

• Observed parasitism jumped from affecting approximately 20% of egg laying females in 2014, 70-80% in 2015, and to almost 100% in 2016.

• Parasitoid wasps were identified as Anagyrus schoenherri.


Little Cherry Virus 2 transmissionGrape mealybug (GMB)

§ Multivoltine

Overwintering egg mass

Adults on shoot

Adult on base of cherry cluster

World Class. Face to Face.Grape mealybug phenology

Petal Fall

Systemic

Summer


Control methods for grape mealybug (GMB)

• GMB-infested 1-yr.-old potted “Bing” trees.§ Treatments:

• Admire Pro - neonicotinoid (drench systemic)• Aza-Direct – azadirachtin (drench systemic)• Ultor – spirotetramat (foliar-systemic) • Centaur - buprofezin (insect growth regulator)

§ Results:• Nymphs§ Admire Pro, Aza-Direct and Centaur reduced populations nearly

to zero after 28 days• Adults§ Admire Pro, Aza-Direct and Centaur reduced populations to zero

after 19 days

• Two most abundant leafhopper vector species were Colladonus geminatus and reductus.

• Greater incidence in neighboring alfalfa field than in orchard.• Peak in alfalfa observed late May/early June for C. geminatus,

early June for C. reductus.• C. reductus increasing in orchard early August.

The Hunt for Leafhopper Vectors of Western X in Washington Cherries: Year One


Indicators of LCD

World Class. Face to Face.Are mealybugs a good indicator of LChV2 infection?

• Only 50% of infected orchards visited in 2014 and 2015 had active MB populations.

§ So….. NO - LChV2 infection is not always correlated with an active MB infestation.

§ The initial infection via insect vectors may have occurred previously, but symptoms become evident only in subsequent years.

Mealybugs collected from LChV2+ trees

++

+ ++

---

--


Are visual symptoms good indicators of infection?§ Can be seen up to 2 weeks

before harvest§ But, can be confusing…..

§ Disease expression is dependent on cherry variety and weather.

§ Partial recovery in fruit appearance.§ Confusion of symptoms with those of

other diseases, and certain types of nutrient deficiencies.

§ Some infected trees are symptomless (Typhoid Mary)

Infected Lapin (WX)


Locating LChV2-infected trees

In orchards with known LChV2 infections:• New infections are close to old ones• Most infected trees show some symptoms, but they

can be subtle


Sampling

World Class. Face to Face.Sampling for LCD• Sample leaves or flag symptomatic

trees/limbs at harvest time.• If symptoms are not visible, take a

representative sample. • Leaf sampling

§ Collect leaves from symptomatic limbs (10 leaves/tree), or two leaves per leader if symptoms are not visible.

• Dormant season sampling § Requires 8 inches of dormant bud wood collected

from each leader (minimum of five bud wood samples per tree).

§ January or February

• Send samples § Clean Plant Center Northwest, Prosser Irrigated

Agriculture Research & Extension Center.

Dormant season sampling

Symptomatic limb


Management

World Class. Face to Face.Removing infected trees/orchards!!• Trees§ Treat trunks with herbicide to avoid re-infection via

root grafting and suckering• Whole orchards§ Ripping§ Fumigation

Leaf samples from suckers tested positive for LChV2

World Class. Face to Face.Reinfection risk of a newly planted orchard

New planting (removed in 2013 and replanted in 2014)Removed in 2015 due to LCDOlder Healthy treesLChV2-‐positive


Overall Conclusions • Vector Control§ There are not many options for organic mealybug control§ Two leafhopper species were identified as local vectors, but

control options have not been explored

• Indicators of LCD infection§ Absence of MB infestation doesn’t correlate with absence of

infection§ Visual symptoms can be confusing§ New infections are likely to be located near old ones

• PCR testing is necessary when monitoring§ Trees that do not show obvious disease symptoms, can still be

infected.§ Representative samples (leaves) should be taken from suspect

trees.§ Infected trees should be promptly removed.


Takeaway management tactics

• Infected trees should be promptly removed!• Remove any additional trees displaying the same visual symptoms.• Revisit infection sites yearly• Control for vectors• Manage for reinfection


For more information……

• Check out our WSU LCD webpage http://treefruit.wsu.edu/crop-protection/disease-management/little-cherry-disease/

• Clean Plant Center NW – Fruit Tree Program, PCR testing lab. http://cpcnw.wsu.edu/virus_lab/pcr-lab-testing/§ Contact Syamkumar Siv Pillai –

[email protected]


Acknowledgements• Beers Lab (WSU TFREC)• WSU Sunrise Orchard Crew• Washington Sweet Cherry Growers• Washington Tree Fruit Research Commission• Oregon Sweet Cherry Commission• California Cherry Board• Stemilt Growers• Washington Department of Agriculture

little cherry disease - wsu tree...

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