and Pierce’s disease management in

Matt Daugherty, Department of Entomology, UC Riverside ([email protected]) 1. Background on , Pierce’s disease, vectors

2. GWSS invasion, management, and current status in California

3. BGSS and PD management in coastal California Xylella fastidiosa -limited bacterium Infects native, ornamental, & weedy plants Threat to several crops (e.g., , almond, , 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 , 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 , 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 () • 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 + 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 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) 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, , 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/