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

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

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

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?

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

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?

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

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

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

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

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

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 Vetch Vicia sativa Buckwheat Fagopyrum esculentum

Effect of cover crops on parasitoid performance Results 1 -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 Redak & Toscano, unpublished data Yellow sticky trap monitoring of GWSS ~450 traps checked weekly Mild PD since program inception

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

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?

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

-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