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

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Presentation on theme: "Management options for sharpshooters in California vineyards Matt Daugherty Department of Entomology UC Riverside."— Presentation transcript:

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

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

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

4 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

5 Management of sharpshooters and Pierces 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

6 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

7 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

8 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

9 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 Redwood Sequoia sempervirens Monterrey pine Pinus radiata Casurina equisetifolia

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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 cold, dry winter warm, wet 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 IrvinMark Hoddle Vetch Vicia sativa Buckwheat Fagopyrum esculentum

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 Yellow sticky trap monitoring of GWSS ~450 traps checked weekly Mild PD since program inception Redak & Toscano, unpublished data

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

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 Pierces disease spread?

26 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

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 dont appear to contribute to secondary pest outbreaks Caveats: -dont 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


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