Rodrigo Almeida Dept. Environmental Science, Policy, and Management

University of California, Berkeley

Historique de l’épidémie causée par

Xylella fastidiosa en Californie

et stratégies de lutte mises en place

Host

Disease

Pathogen Host

Time

Vector

What factors affect plant disease epidemics?

Pathogen

Plant Vector

Layers of ecological complexity:

environment (e.g. temperature)

vector ecology

pathogen ecology

host plant ecology

outcome of various interactions

disease management

Today…

• Overview of Xylella fastidiosa

• Case study:

– Pierce’s disease of grapevines in California

• Ecology

• Management strategies

• Management at State level

“California Vine Disease”: First detected in Anaheim in 1884 and in the San Joaquin Valley in 1917

Newton B. Pierce

Pierce’s disease costs California US$104 million per year (Tumber et al. 2014. Calif. Agric. 68, 20-29)

Xylella fastidiosa

Xylella fastidiosa

• Xylem-limited bacterium

• Colonizes a wide range of host plants, usually

without causing disease

• Present in the Americas, Taiwan, Italy, France, Iran

– Causing disease in grape at least since the 1880s

– Major crops affected

• Grape, citrus, alfalfa, peach, almond, plum, coffee, etc

• Xylem sap-feeding insects are only vectors

• Pierce’s disease in grapes

• Alfalfa dwarf

• Almond leaf scorch

• Phony peach disease

• Plum leaf scald

• Citrus variegated chlorosis

• Elm, oak, sycamore leaf scorch

• Oleander leaf scorch

* and a very large list of new emerging

diseases of crops and ornamentals

Plant colonization

Newman et al. 2003 Appl. Env. Microbiol.

Vectors: xylem sap feeding insects

Today…

• Overview of Xylella fastidiosa

• Case study:

– Pierce’s disease of grapevines in California

• Ecology

• Management strategies

• Management at State level

Here I will focus on one disease caused by X. fastidiosa in California. It

should be mentioned that diseases such as oleander leaf scorch and

almond leaf scorch, for example, are very important as well as and

caused by other genotypes of this pathogen.

In addition, in other areas of the USA, X. fastidiosa causes diseases of

economic importance on a variety of plants, from pecans and blueberries

to oaks and elm trees.

What is the X. fastidiosa that causes

Pierce’s disease of grapevine in the USA?

late 1800s

1930s -40s

late 1990s

early 2000s

Late 1800s: Anaheim vine disease

1930s and 40s: Central Valley -alfalfa

Late 90s - early 2000s: Temecula Valley and Kern County -invasive GWSS

North coast: consistent, moderate PD -native BGSS

Severe Pierce’s disease outbreaks are unusual

Photo A.H. Purcell

Pierce’s disease epidemiology

- what we know for Northern California-

How do farmers in Northern California

manage Pierce’s disease today?

Management action % growers

Insecticides in vineyard 17.67

Insecticides outside vineyard 1.51

Roguing 38.88

Severe pruning 3.53

Weed control 3.53

Riparian management 8.58

Vector or Disease Monitoring 14.64

How much do farmers in Northern California

believe they are loosing to Pierce’s disease today?

What happened in Southern California?

Glassy-winged sharpshooter invaded ~1990 By late 90s GWSS populations were tremendous

-”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 overall

Glassy-winged sharpshooter

(Homalodisca vitripennis)

Photo A.H. Purcell

Temecula Valley, CA -3 years after first symptomatic plant-

General impact of GWSS introduction into California

GWSS large populations

More X. fastidiosa-vector encounters

More successful infections New vector-pathogen associations?

and/or

New X. fastidiosa strains?

Higher disease incidence

New diseases

The response to the Temecula outbreak

Replanted majority of acreage

-removed inoculum source Area-wide vector control

1. sharpshooter monitoring

2. biological control

3. chemical control in citrus Appropriate vineyard management

-vine removal

-vector control

Chemical control of GWSS

Two scales of chemical control of GWSS 1. Area-wide application of insecticides to citrus

-citrus is a preferred reproductive hosts -strong gradient in Pierce’s disease risk as a function of vineyard proximity to citrus

2. Application of insecticides to individual vineyards -treat grapevines to reduce vector pressure

Area-wide treatment of citrus

Reducing disease risk for vineyards requires cooperation of citrus growers ~2000 acres grapevines, ~1000 acres of citrus in Temecula Since 2000, up to 1000+ acres of citrus treated with insecticides (primarily imidacloprid)

-significant reductions in vector pressure in vineyards next to treated citrus -regional GWSS populations are a greatly reduced since the program started

X

Chemical control of GWSS

Area-wide treatments in citrus to limit GWSS incursion into vineyards Grape-growers also commonly treat grapevines as a means of further reducing vector pressure >70% of Temecula vineyards treated consistently with imidacloprid

Response to the Temecula outbreak

GWSS populations are greatly reduced compared to 15 years ago

Pierce’s disease prevalence is currently very low

<1% on average, treated fields lower

<0.01

Main Pierce’s disease management options in California? Monitor regularly for sharpshooters

Conventional or organic foliar insecticides

-timing based on monitoring data

Within-vineyard weed control?

Remove diseased vines to ensure they are not sources of infection

Management of riparian plants

Today…

• Overview of Xylella fastidiosa

• Case study:

– Pierce’s disease of grapevines in California

• Ecology

• Management strategies

• Management at State level

Pierce’s Disease Control Program

Mission & Strategy Mission: Minimize the statewide impact of

Pierce’s disease in California.

Strategy: Contain the spread of the new

vector to allow time to develop solutions.

Host

(Grapes) Vector

(GWSS)

Pathogen (Xf)

Tom Esser, CDFA

How is management done in

California at the State level?

Components

• Containment

• Statewide Survey

• Rapid Response

• Public Outreach

• Research

Activities

• Biological Control

• Area-wide Projects Tom Esser, CDFA

Cooperative Program

• USDA

• CDFA

• County Agricultural Commissioners

• University of California

• Industry Groups

• Stakeholders

• Public

Tom Esser, CDFA

GWSS in California

June 2002

Tom Esser, CDFA

Containment

Nursery Bulk Citrus Bulk Grape

• Prevent GWSS from moving to new areas

Tom Esser, CDFA

Statewide Survey

• Verify that at-risk areas are still uninfested

• Look for new/unknown infestations of GWSS

• Currently being conducted in 49 counties (6 generally infested, 36 uninfested, 7 partially infested)

• Approximately 38,000 traps deployed in nursery

and urban/residential areas during peak season

Tom Esser, CDFA

Rapid Response

• Delimitation, regulatory, treatment, & monitoring

• 17 infestations eradicated

Tom Esser, CDFA

Public Outreach

• Meetings, brochures, website, mailings, news

stories, word-of-mouth, posters, etc.

• Awareness and compliance increased rapidly;

public helped discover new infestations

Tom Esser, CDFA

Research

• Over 200 projects conducted since 1999

• 13 Symposia held; 990 reports in 15 years

of Proceedings

• Field trials in progress

Tom Esser, CDFA

Funding for PD/GWSS (cumulative, 17 years)

$440 497 000

$66 966 000

$56 692 000

$2 171 000

Federal State Industry Local

Tom Esser, CDFA

Uses of Industry PD/GWSS Assessment Funds (Cumulative, 15 years)

$29 024 000

$7 240 000

$3 997 000

$3 645 000

$3 184 000

$2 681 000 $1 265 000

Basic Research Applied Research & Field Trials

Program Support Administration & Grower Votes

Research-Related Services Public Outreach

Other Designated Pests & Diseases

Tom Esser, CDFA

Take home messages…

. California has ‘four’ X. fastidiosa problems that are very different from each other:

. Pierce’s disease in Northern California, has been a problem for 100 years, new

epidemic ongoing.

. Pierce’s disease in Southern California, now driven by an introduced vector,

major effort by state/federal governments to control it.

. Small epidemics of almond leaf scorch and oleander leaf scorch, which are

localized and have limited impact.

. Unknown or poorly characterized diseases, such as urban trees and trees in

California forests.

. Millions have been invested in pest monitoring, area wide control efforts, research,

outreach and extension (last 15 years). However, there is still no cure to X. fastidiosa

infection of grapevines. Despite all recent efforts, epidemics have emerged in the last

couple of years in Northern and Southern California. The best alternative, in my opinion,

is an integrated approach to disease management that includes a range of strategies to

control vectors and reduce pathogen prevalence in the environment.

. Advice? Invest in monitoring, research, outreach, and extension. Support all disciplines

and approaches, do not ignore paths that seem ‘traditional’ or ‘cutting edge’. Different X.

fastidiosa diseases are handled in different ways in different crops and parts of the world.

Each solution is system and location based, there is no ‘one size fits all’ answer. But all

answers integrate plant, insect, pathogen, social, economic, environmental and

agricultural practices.