little cherry disease - wsu tree...
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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
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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
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Little Cherry Disease (LCD)
• Symptoms§ Produce cherries
of small size and poor color and flavor
• Results§ Economic losses§ Tree and orchard
removal
Bing Cherries
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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
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Little Cherry Virus 2 transmissionApple mealybug (AMB) - Univoltine
Egg masses on apple
Egg mass
Crawlers on underside of leaf
Adults
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Apple mealybug control 2014
DelayedDormant
Systemic Petal Fall
Foliar Crawler
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Apple mealybug control 2015
Foliar Crawler
Systemic Petal Fall
DelayedDormant
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• 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.
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Little Cherry Virus 2 transmissionGrape mealybug (GMB)
§ Multivoltine
Overwintering egg mass
Adults on shoot
Adult on base of cherry cluster
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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
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
++
+ ++
---
--
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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)
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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
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
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
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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.
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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
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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 –