Detecting and Managing Little Cherry Disease Organic Pest and Disease Management Fruit School March 15, 2017 Andrea Bixby-Brosi and Elizabeth Beers: Entomology, Wenatchee, WA Ken Eastwell and Dan Villamor: Plant pathology, Prosser, WA Tim Smith: Regional Extension Specialist, Wenatchee, WA
Roadmap 1. Introduction 2. Insect vectors: apple mealybug (AMB), grape mealybug (GMB), and leafhoppers. 3. Insect control 4. 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
Aerial photos showing loss due to LCD 2011 2013 2015
Another example of Loss due to LCD 2009 2013 2011 2006 2015
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
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 transmission Apple mealybug (AMB) - Univoltine Egg masses on apple Adults Crawlers on underside of leaf Egg mass
Apple mealybug phenology Foliar Crawler Delayed Dormant Systemic
Apple mealybug control 2014 Foliar Crawler Systemic Petal Fall Delayed Dormant
Apple mealybug control 2015 Foliar Crawler Systemic Petal Fall Delayed Dormant
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 transmission Grape mealybug (GMB) Multivoltine Adults on shoot Adult on base of cherry cluster Overwintering egg mass
Grape mealybug phenology Petal Fall Summer Systemic
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
The Hunt for Leafhopper Vectors of Western X in Washington Cherries: Year One 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.
Indicators of LCD
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
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. Symptomatic limb Dormant season sampling
Management
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
Reinfection risk of a newly planted orchard New planting (removed in 2013 and replanted in 2014) Removed in 2015 due to LCD Older Healthy trees LChV2- 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/cropprotection/disease-management/little-cherrydisease/ Clean Plant Center NW Fruit Tree Program, PCR testing lab. http://cpcnw.wsu.edu/virus_lab/pcr-labtesting/ Contact Syamkumar Siv Pillai syam_skumar@wsu.edu
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