1. Management options for sharpshooters in California vineyards
Matt Daugherty
Department of Entomology
UC Riverside

2. Disease management vector 1. Eliminate pathogen sources
2. Resistant hosts
3. Vector control
vector
host
pathogen

3. Disease management Sharpshooters 1. Eliminate pathogen sources
2. Resistant hosts
3. Vector control
Xylella
host species
or varieties
Xylella strains

4. Pest damage: Direct vs. Indirect
Direct: damage is a function of pest # and time
Indirect: damage weakly linked to pest number
-a few individuals can cause severe damage
-is disease management via vector control achievable?

5. Management of sharpshooters and Pierce’s disease
Seasonality constrains PD spread
-late-season infections recover overwinter
Sharpshooter impact largely tied to abundance
-limiting GWSS pops limits disease spread
PD management should be achievable

6. 1. Can physical barriers limit sharpshooter movement into vineyards?
2. Enhancing the impact of parasitoids on GWSS
3. How necessary is within-vineyard chemical control?

7. Barrier plantings for vector-borne disease management
-plants along the periphery limit disease spread into a focal field
Pathogen sinks
-barriers clear vectors of infection
-non-persistent aphid-borne viruses
Physical barrier
-barriers obstruct vector movement into focal crop
-defined vector source

8. 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
Blue-green sharpshooter
Graphocephala atropunctata

9. Green barriers to BGSS movement into vineyards
Redwood
Sequoia sempervirens
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
Monterrey pine
Pinus radiata
Casurina equisetifolia

11. Substantial seasonal and year-to-year variability in BGSS abundance
-peak in April/May

12. Why such big differences in BGSS among years? Climate
warm, wet
winter
cold, dry
winter
-warm, wet winters may encourage more BGSS and PD the next season

13. 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

14. 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)

15. 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

16. 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

17. 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
Vetch
Vicia sativa
Buckwheat
Fagopyrum esculentum

19. Effect of cover crops on parasitoid performance
Results 1
-cover crops enhance parasitoid performance
-buckwheat more beneficial

20. 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

21. 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

22. 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

23. Temecula area-wide control program
Proximity to citrus affects PD severity
~2000 acres grapevines, ~1000 acres of citrus
Since 2000, up to acres of citrus treated (imidacloprid)
-significant reductions in vector pressure
Redak & Toscano, unpublished data
Yellow sticky trap monitoring of GWSS
~450 traps checked weekly
Mild PD since program inception

24. X Chemical control of GWSS
Treatments in citrus limit GWSS incursions into vineyards
Are within-vineyard treatments further beneficial? X

25. 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?

26. Field surveys of PD prevalence
Adam
Tracy
Field surveys of PD prevalence
34 sites with known treatment history
Treated, untreated, mixed treatment
Verify imidacloprid treatments
Visual symptoms, culture symptomatic, ELISA asymptomatic
GWSS and natural enemy monitoring

27. -ELISA assay to verify imidacloprid concentration
-regularly treated vineyards had higher concentration than intermittently treated vineyards

28. -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

29. -abundance of most common generalist predators was not affected by treatment
-no obvious secondary pest outbreaks

30. 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?

31. 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