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