4 Pest damage: Direct vs. Indirect Direct: damage is a function of pest # and timeIndirect: 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 overwinterSharpshooter impact largely tied to abundance-limiting GWSS pops limits disease spreadPD management should be achievable
6 1. Can physical barriers limit sharpshooter movement into vineyards? 2. Enhancing the impact of parasitoids on GWSS3. 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 fieldPathogen sinks-barriers clear vectors of infection-non-persistent aphid-borne virusesPhysical barrier-barriers obstruct vector movement into focal crop-defined vector source
8 Barriers to sharpshooter movement Decent fliersMost 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 corridorsBlue-green sharpshooterGraphocephala atropunctata
9 Green barriers to BGSS movement into vineyards RedwoodSequoia sempervirensGreen barriers to BGSS movement into vineyardsVineyard adjacent to Napa River-blue-green sharpshooter4 treatments:-open controls (no obstruction)-redwood-Casurina-Monterrey pineTraps on vineyard & riparian sidesMonitored ~2x month for 8 yearsMonterrey pinePinus radiataCasurina 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, wetwintercold, drywinter-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 habitatGreen 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 effectiveSeveral parasitoid wasps occur in CA-egg parasitoids-mass releaseMost effective is G. ashmeadi-up to 80% parasitism
16 Adult wasps require additional resources -carbohydratesAlternative resources-survival, egg production,female production higherwith access to alternativeresourcesCover crops as way of enhancing biological control-conservation biocontrol
17 Using vineyard cover crops to enhance GWSS biocontrol 1. Effect of cover crops on parasitoidperformance-control, vetch, buckwheat2. Cover crop effect on natural enemies & pests-field experiment-control, water, water + buckwheat3. Water and cover crop effect onvine vigor and yieldNic IrvinMark HoddleVetchVicia sativaBuckwheatFagopyrum 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 effectCover crop doesn’t reduce leafhoppers and other pest abundance
21 Biocontrol is an important component of GWSS IPM -under ideal conditions G. ashmeadi cansuppress GWSSCover crops can provide beneficial resources-limited effect in encouraging retention ofnatural enemies-limited effect on pest suppressionCover 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 citrusGWSS is highly susceptible to systemic insecticides (imidacloprid)-imidacloprid readily transported in xylem-GWSS process 100 to 1000x body weight dailyArea-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 citrusSince 2000, up to acres of citrus treated (imidacloprid)-significant reductions in vector pressureRedak & Toscano, unpublished dataYellow sticky trap monitoring of GWSS~450 traps checked weeklyMild PD since program inception
24 X Chemical control of GWSS Treatments in citrus limit GWSS incursions into vineyardsAre 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 imidaclopridLittle data on whether vector pressure is affectedNo information linking treatments with PD spreadDoes within-vineyard chemical control reduce vector pressure and Pierce’s disease spread?
26 Field surveys of PD prevalence AdamTracyField surveys of PD prevalence34 sites with known treatment historyTreated, untreated, mixed treatmentVerify imidacloprid treatmentsVisual symptoms, culture symptomatic, ELISA asymptomaticGWSS 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 sitesTreatments don’t appear to contribute to secondary pest outbreaksCaveats:-don’t have incidence measures-treatment may not always be necessary-what if regional GWSS population is much larger?
31 Nick ToscanoGevin KenneyFrank ByrneNic IrvinTracy PinckardBarrett GruberAdam ZeilingerBen DrakeUSDA-CSREESConsolidated Central Valley Pest & Disease Management DistrictCDFA and UC GWSS/PDprogram