Sharpshooter and Pierce’s disease management in California vineyards
Matt Daugherty, Department of Entomology, UC Riverside ([email protected]) 1. Background on Xylella fastidiosa, Pierce’s disease, vectors
2. GWSS invasion, management, and current status in California
3. BGSS and PD management in coastal California Xylella fastidiosa Xylem-limited bacterium Infects native, ornamental, & weedy plants Threat to several crops (e.g., grapes, almond, citrus, alfalfa)
Xylella diseases Plugs xylem vessels, restricts water flow
Leaf scorch or stunting symptoms vary among hosts (Pierce’s disease in grapes, Alfalfa dwarf)
No cure Pierce’s disease
“matchstick” leaf scorch petioles
“green raisined islands” clusters
defoliation, dieback Xylella fastidiosa transmission
Transmitted by xylem sap-feeding insects • some leafhoppers, spittlebugs
No transovarial transmission
No latent period
Nymphs & adults can transmit • no transmission after molting • persistent in adults
Vector species differ in efficiency • depends on Xylella strain, host plant Blue-green sharpshooter (Graphocephala atropunctata)
Dominant vector of Xylella in the coast range
Strong association with riparian habitats • wild grape, blackberry, mugwort….
Becomes active in vineyards in Spring, when days become warmer • multiple days > 65°F • peak ~May, smaller peak mid-Summer
Typically does not travel too far into vineyards; PD along margins Glassy-winged sharpshooter (Homalodisca vitripennis)
Native to SE USA
First documented in CA in 1989
Spread throughout S. CA, S. Central Valley, select areas further North
Extremely broad host range -350+ plant taxa on CDFA list https://www.cdfa.ca.gov/pdcp/Documents/HostListCommon.pdf
Relatively inefficient vector of Xylella Glassy-winged sharpshooter (Homalodisca vitripennis)
Relatively inefficient at transmitting Xylella, but…
• more active throughout the year
• willing to feed on woody plant material
• able to fly further than other vectors
• multiple generations a year
• capable of very high population growth rates Other native vectors
Smoke tree sharpshooter (Homalodisca liturata) • present in interior, S. CA • much less abundant than GWSS • modest transmission efficiency
Green sharpshooter (Draeculacephala minerva) • prefers grasses, sedges • common in irrigated pastures and ditches • important vector for alfalfa & almond, less efficient to grapevines Other native vectors
Red-headed sharpshooter (Xyphon fulgida) • prefers grasses (esp. Bermuda grass) • locally abundant where weedy grasses occur • moderate efficiency
Meadow spittlebug (Philaenus spumarius) • cosmopolitan xylem-sap feeder • appearance varies • locally abundant on some forbs and grasses • low transmission efficiency? Factors aiding/undermining PD management
+ vectors must acquire from infected plant to be infective + pruning is not an important source of Xylella spread + no evidence of root-graft transmission + cold winters encourage recovery of some vines
- can’t prune out PD infections - resistant/tolerant varieties not yet available - no therapeutic cure for infected vines
PD management relies on 1) suppressing vector populations and 2) limiting pathogen supply
What happened in Temecula Valley?
By late 90s extremely high GWSS populations
•”100s to 1000s” per vine • proximity to citrus
Severe Pierce’s disease outbreaks • up to 100% infection within a year ~40% loss for Temecula region
Similar epidemic in S. Central Valley in early 2000s Response to GWSS-mediated PD outbreaks
Area-wide vector control 1. sharpshooter monitoring 2. biological control 3. chemical control in citrus
Quarantines on plant material • limit transport of GWSS
Vineyard management •vector control •removal of disease vines •weed management Monitoring for sharpshooters
Monitoring is important for identifying location and timing of insecticide applications
1. Deploy sticky traps along margins of blocks, particularly near suspected sources • citrus + ornamentals for GWSS; riparian + ornamentals for BGSS • check traps twice a month
2. Sweep-net sampling on vineyard floor and surrounding edges • esp. areas with weedy grasses Biological control of GWSS
Introduced Mymarid egg parasitoids • Cosmocomoidea (=Gonatocerus) spp.
CDFA program for 15+ years • not commercially available
7 species in total, 3 currently • C. morgani, C. ashmeadi, C. morrilli
Mass reared and released throughout GWSS range
Parasitism upwards of 80% in late season Chemical control of GWSS Citrus is a preferred host for GWSS
Area-wide treatments in citrus limit GWSS incursions into vineyards
Primarily systemic neonicotinoids, with additional foliar applications (i.e. pyrethroids) in some cases Insecticides for sharpshooter control include conventional systemics and foliars, and organics http://www.ipm.ucdavis.edu/PMG/r302301711.html
Imidacloprid, dinotefuran, thiamethoxam, fenpropathrin…. -systemics can have long residual efficacy (i.e. months)
Pyrethrins, kaolin -short residual efficacy (week-10 d retreatment) Weed control in and around vineyards
Common weedy grasses can be vector sources • irrigation/roadside ditches, leaky irrigation
• Bermuda grass • green, red-headed sharpshooter
Several weeds are Xylella reservoirs • morning glory, poison hemlock, prickly lettuce, Datura, mustards, broom Removal of diseased vines
Roguing diseased vines ensures they aren’t a pathogen source
Scout for disease in the Fall, when symptoms are strongest
Flag vines showing extensive, convincing set of PD symptoms for later removal
Note questionable vines and follow them the next season. Effectiveness of GWSS & PD management
GWSS populations greatly reduced compared to 15+ years ago
Pierce’s disease prevalence is also substantially reduced <1% on average, majority of blocks had no PD A GWSS resurgence?
After several years of low densities, GWSS populations are starting to rebound in certain areas
• Kern and Tulare Co. GWSS more than 5-fold higher since 2011 • In Temecula peak catch in 2017 was greatest in 15 years GWSS insecticide resistance
Ongoing research is evaluating GWSS susceptibility to systemic neonicotinoids and pyrethroids
F. Byrne, UCR
Tulare (red/green) and especially Kern (blue) Co. are far less susceptible to imidacloprid than historical GWSS (black)
PD management in the coast range
Riparian habitat is a key source of BGSS • ornamentals, other potential sources
BGSS doesn’t fly far into vineyards, doesn’t spend much time in vineyards
Management focuses on reducing primary spread from source habitat
Recent increase in PD prevalence in North Coast vineyards • different patterns of disease
riparian site in Sonoma Co. PD management in the coast range
Vector monitoring
Biological control ?
Chemical control
Weed management (GSS, RHSS, MSB)
Vine roguing ?
Barriers to sharpshooter movement ?
Riparian management Strategies for GWSS chemical control may not translate well to coastal vineyards
More clay-rich soils and limited watering minimize systemic insecticide uptake in the North Coast
Weber et al. 2005
• < 2 % of samples ever reached 10 ppb Strategies for GWSS chemical control may not translate well to coastal vineyards
More clay-rich soils and limited watering minimize systemic insecticide uptake in the North Coast
• imidacloprid rarely gets to the root zone
• more soluble systemic neonic (dinotefuran) might be more effective
Foliar insecticides play a more important role
• late-spring, mid-summer applications based on monitoring
• spring application of OP (dimethoate) to riparian plants Monitoring for sharpshooters
Monitoring is important for identifying location and timing of insecticide applications
1. Deploy sticky traps near edge or in transects away from source habitat • riparian + ornamentals for BGSS
• check traps twice a month, or more often in the Spring
2. Sweep-net sampling on vineyard floor and surrounding edges • esp. areas with weedy grasses Riparian vegetation management
At many sites, riparian corridors are the source of BGSS
Management involves targeted removal of key hosts plants
Removal of reproductive hosts can dramatically reduce BGSS density • by upwards of 90%
• more effective than insecticides
Also may reduce somewhat pathogen supply Key host plants: Riparian vegetation management manual: https://nature.berkeley.edu/xylella/control/PDNorthCoast/
Long-term management strategy
• permitting by CDFW
Requires vigilance to continue to reap benefits http://www.cnr.berkeley.edu/xylella/ http://www.ipm.ucdavis.edu/PMG/r302301711.html http://www.piercesdisease.org/ http://www.cdfa.ca.gov/pdcp/