Sharpshooter and Pierce s disease management in California vineyards. Matt Daugherty, Department of Entomology, UC Riverside

Transcription

1 Sharpshooter and Pierce s disease management in California vineyards Matt Daugherty, Department of Entomology, UC Riverside (mattd@ucr.edu)

2 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

3 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

4 Pierce s disease leaf scorch matchstick petioles green islands raisined clusters defoliation, dieback

5 Transmitted by xylem sap-feeding insects some leafhoppers, spittlebugs No transovarial transmission No latent period Nymphs & adults can transmit Xylella fastidiosa transmission no transmission after molting persistent in adults Vector species differ in efficiency depends on Xylella strain, host plant

6 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

7 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 plant taxa on CDFA list Relatively inefficient vector of Xylella

8 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

9 Smoke tree sharpshooter (Homalodisca liturata) present in interior, S. CA much less abundant than GWSS modest transmission efficiency Other native vectors Green sharpshooter (Draeculacephala minerva) prefers grasses, sedges common in irrigated pastures and ditches important vector for alfalfa & almond, less efficient to grapevines

10 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?

11 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

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13 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

14 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

15 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

16 Introduced Mymarid egg parasitoids Cosmocomoidea (=Gonatocerus) spp. CDFA program for 15+ years not commercially available 7 species in total, 3 currently Biological control of GWSS C. morgani, C. ashmeadi, C. morrilli Mass reared and released throughout GWSS range Parasitism upwards of 80% in late season

17 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

18 Insecticides for sharpshooter control include conventional systemics and foliars, and organics Imidacloprid, dinotefuran, thiamethoxam, fenpropathrin. -systemics can have long residual efficacy (i.e. months) Pyrethrins, kaolin -short residual efficacy (week-10 d retreatment)

19 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

20 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.

21 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

22 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

23 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)

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25 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.

26 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

27 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 < 2 % of samples ever reached 10 ppb

28 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

29 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

30 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

31 Key host plants:

32 Riparian vegetation management manual: Long-term management strategy permitting by CDFW Requires vigilance to continue to reap benefits

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