management options for sharpshooters in california vineyards matt daugherty department of entomology...
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Management options for sharpshooters in California vineyards
Matt DaughertyDepartment of Entomology
UC Riverside
vector
pathogen host
Disease management
1. Eliminate pathogen sources
2. Resistant hosts
3. Vector control
Sharpshooters
Xylella host speciesor varieties
Xylella strains
Disease management
1. Eliminate pathogen sources
2. Resistant hosts
3. Vector control
Pest damage: Direct vs. Indirect
Indirect: damage weakly linked to pest number
-a few individuals can cause severe damage
-is disease management via vector control achievable?
Direct: damage is a function of pest # and time
Management of sharpshooters and Pierce’s disease
1. Seasonality constrains PD spread
-late-season infections recover overwinter
2. Sharpshooter impact largely tied to abundance
-limiting GWSS pops limits disease spread
PD management should be achievable
3. How necessary is within-vineyard chemical control?
1. Can physical barriers limit sharpshooter movement into vineyards?
2. Enhancing the impact of parasitoids on GWSS
Barrier plantings for vector-borne disease management
1. Pathogen sinks
-barriers clear vectors of infection
-non-persistent aphid-borne viruses
2. Physical barrier
-barriers obstruct vector movement into focal crop
-defined vector source
-plants along the periphery limit disease spread into a focal field
Blue-green sharpshooter
Graphocephala atropunctata
Barriers to sharpshooter movement
Decent fliers
Most fly close to the ground (95% ≤5m)
Artificial barrier can interrupt sharpshooter movement (<7% flew over 5m screen)
Clearly defined vector sources
-GWSS: citrus groves
-BGSS: riparian corridors
Green barriers to BGSS movement into vineyards
Vineyard adjacent to Napa River-blue-green sharpshooter
4 treatments:-open controls (no obstruction)-redwood-Casurina-Monterrey pine
Traps on vineyard & riparian sides
Monitored ~2x month for 8 years
RedwoodSequoia sempervirens
Monterrey pinePinus radiata
Casurina equisetifolia
Substantial seasonal and year-to-year variability in BGSS abundance
-peak in April/May
Why such big differences in BGSS among years? Climate
cold, drywinter
warm, wetwinter
-warm, wet winters may encourage more BGSS and PD the next season
Large differences in BGSS trap catches among years
Significant reductions in BGSS caught behind barriers in some years
-by up to half in some years-redwood most effective
Green barriers have the potential to reduce sharpshooter movement into vineyards
-inconsistent effect among years
-big enough effect to reduce PD spread?
Effective for GWSS?
-identify source habitat
Green barrier characteristics
-grow quickly -low “permeability”
-poor GWSS hosts -poor Xylella reservoirs (not citrus, almond, olive, photinia, crepe myrtle)
Glassy-winged sharpshooter biological control
Many generalist natural enemies of GWSS
-not very effective
Several parasitoid wasps occur in CA
-egg parasitoids
-mass release
Most effective is G. ashmeadi
-up to 80% parasitism
Adult wasps require additional resources
-carbohydrates
Alternative resources
-survival, egg production, female production higher with access to alternative resources
Cover crops as way of enhancing biological control
-conservation biocontrol
Using vineyard cover crops to enhance GWSS biocontrol
1. Effect of cover crops on parasitoid performance
-control, vetch, buckwheat
2. Cover crop effect on natural enemies & pests
-field experiment
-control, water, water + buckwheat
3. Water and cover crop effect on vine vigor and yield
Nic Irvin Mark Hoddle
VetchVicia sativa
BuckwheatFagopyrum esculentum
Results 1
1. Effect of cover crops on parasitoid performance
-cover crops enhance parasitoid performance
-buckwheat more beneficial
2. Effect of cover crops on pest & natural enemy abundance
Cover crop slightly increases natural enemy abundance -irrigation effect
Cover crop doesn’t reduce leafhoppers and other pest abundance
Biocontrol is an important component of GWSS IPM
-under ideal conditions G. ashmeadi can suppress GWSS
Cover crops can provide beneficial resources
-limited effect in encouraging retention of natural enemies
-limited effect on pest suppression
Cover crops (vetch and buckwheat) were not favored by GWSS
-reservoirs for Xylella
Chemical control of GWSS
GWSS’s impact largely occurs because of high populations
-proximity to citrus
GWSS is highly susceptible to systemic insecticides (imidacloprid)
-imidacloprid readily transported in xylem
-GWSS process 100 to 1000x body weight daily
Area-wide chemical control has reigned in PD outbreak
Temecula area-wide control program
Proximity to citrus affects PD severity~2000 acres grapevines, ~1000 acres of citrus
Since 2000, up to 1000+ acres of citrus treated (imidacloprid)
-significant reductions in vector pressure
Yellow sticky trap monitoring of GWSS ~450 traps checked weekly
Mild PD since program inception
Redak & Toscano, unpublished data
X
Chemical control of GWSS
Treatments in citrus limit GWSS incursions into vineyards
Are within-vineyard treatments further beneficial?
Within-vineyard control
Chemical control commonly employed in vineyards for GWSS control
>70% of Temecula vineyards treated consistently with imidacloprid
Little data on whether vector pressure is affected
No information linking treatments with PD spread
Does within-vineyard chemical control reduce vector pressure and Pierce’s disease spread?
Adam Tracy
34 sites with known treatment history
Treated, untreated, mixed treatment
Verify imidacloprid treatments
Visual symptoms, culture symptomatic, ELISA asymptomatic
GWSS and natural enemy monitoring
Field surveys of PD prevalence
-ELISA assay to verify imidacloprid concentration
-regularly treated vineyards had higher concentration than intermittently treated vineyards
-GWSS more abundant than STSS
-most sharpshooters in untreated
-least sharpshooters in intermittently treated
-corrected % of vines infected
-low prevalence overall
-trend towards more disease in untreated sites
-abundance of most common generalist predators was not affected by treatment
-no obvious secondary pest outbreaks
Within-vineyard chemical control may reduce disease spread
-lower vector pressure in treated sites
-lower prevalence in treated sites
Treatments don’t appear to contribute to secondary pest outbreaks
Caveats:
-don’t have incidence measures
-treatment may not always be necessary
-what if regional GWSS population is much larger?
Nick Toscano
Gevin Kenney
Frank Byrne
Nic Irvin
Tracy Pinckard
Barrett Gruber
Adam Zeilinger
Ben Drake
USDA-CSREES
Consolidated Central Valley Pest & Disease Management District
CDFA and UC GWSS/PD program
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