California Citrus Nursery Board

5.6—Industry Organizations

Central California Tristeza Eradication Agency

CENTRAL CALIFORNIA TRISTEZA ERADICATION AGENCY

OVERVIEW

The Central California Tristeza Eradication Agency, formed in 1963, is charged with the survey, detection and eradication of citrus tristeza virus (CTV) within participating Pest Control Districts. They represent approximately 140,000 commercial citrus producing acres within portions of Fresno and Tulare counties, and all of Kern County. The mission of these districts, united in a Joint Powers Agreement, is the detection and removal of CTV infected trees. This active, mandatory suppression program provides the greatest protection possible through enforcement of quarantine regulations, and ultimately, helps to maintain a strong and globally competitive fresh citrus industry.

The Agency is governed by a Board of Commissioners comprised of representatives of each of the JPA districts. The Technical Advisory Committee, a panel of UC, USDA, and CDFA scientists and CDFA and County regulatory personnel, provides scientific and technical expertise.

The CCTEA employs a staff of 17 regular and up to 40 seasonal workers. During the 2007-2008 fiscal year, these employees will be responsible for surveying approximately 20,000 acres and conducting up to 223,000 individual ELISA assays in the Agency’s laboratory facility. Diagnostic services are also provided on a contract agreement basis for individual growers, researchers, nurserymen, and concerned governmental entities, including the CDFA, the County of Riverside and the West Fresno County Red Scale Protective District.

As a grower-funded program, growers are charged a special assessment on their commercial citrus acreage. The special assessment appears on the annual property tax bill, and is calculated on a 100-tree-acre basis. The assessment is computed by County Auditors, based on budgets independently established by each pest control district. Fiscal year 2007-2008 district assessments range from $9.50 in the Central Valley Pest Control District, to $10.76 in the Kern County Citrus Pest Control District, to $11.42 in the Southern Tulare County Citrus Pest Control District.

In addition, the individual districts pay compensation directly for the infected trees removed within their boundaries. Since December 1999, the Agency’s tree removal policy has defined tree removal as the elimination of both the scion and rootstock. Currently, pursuant to the State Ag Code, a maximum of $25 compensation (adjusted for tree age) is paid for each infected tree, if the grower removes the scion. In the Central Valley and Southern Tulare County Citrus Pest Control Districts, growers are offered an additional $25 per tree if they also complete the rootstock removal.

The CCTEA Board of Commissioners and staff wish to thank the citrus growers throughout the three pest control districts for their high level of cooperation with the survey and eradication effort.

Central California Tristeza Eradication Agency (CCTEA)

CCTEA

Jill Barnier, Program Manager
jbarner@cdfa.ca.gov

The Central California Tristeza Eradication Agency, formed in 1963, is charged with the survey, detection and eradication of citrus tristeza virus (CTV) within participating Pest Control Districts. They represent approximately 111,000 commercial citrus producing acres within portions of Fresno, Tulare, and Kern counties. The Agency is governed by a Board of Commissioners comprised of representatives of each of the JPA districts. It employs a staff of 22 regular and up to 35 seasonal employees. During the 2000–2001 fiscal year, these employees will be responsible for surveying approximately 31,400 acres and conducting up to 375,000 individual ELISA assays in the Agency’s laboratory facility.

Diagnostic services are also provided on a contract agreement basis for individual growers, nurserymen, and other governmental entities, including the State of Arizona and the County of Riverside. As a grower-funded program, growers are charged a special assessment on their commercial citrus acreage. The special assessment appears on the annual property tax bill, and is calculated on a 100–tree–acre basis. The assessment is computed by County Auditors, based on budgets independently established by each pest control district. In addition, the individual districts pay compensation directly for the infected trees removed within their boundaries. Currently, pursuant to the State Ag Code, a maximum of $25 compensation (adjusted for tree age) is paid for each infected tree, if removed by the grower. In December 1999, the Board revised the tree removal policy to define tree removal as the elimination of both the scion and rootstock. Unless special circumstances exist, CTV–infected trees must be removed using a backhoe or similar equipment.

Central California Tristeza Eradication Agency

Effective Plan

July 1, 2007 Revision

Background

The purpose of the Central California Tristeza Eradication Agency is to identify and eradicate Citrus tristeza virus (CTV) in a timely, orderly and cost–effective manner. Toward this end, during 1992–1995, the Effective Plan for the Agency included a systematic subsampling survey of all commercial citrus trees. The goal was to identify areas with infected trees and estimate the extent of disease incidence. The results from this survey were compiled into a Collection Priority List (CPL). This list, sorted from the highest level of infection to the lowest, served as the basis for the more aggressive Effective Plan for July 1995 through June 1998.

The operational objectives of the 1995–1998 Effective Plan were (1) "to achieve effective eradication in the three participating pest control districts by identifying and removing CTV positive trees more rapidly than the estimated rate of disease increase"; that is, to annually remove more than 50% of existing CTV positive trees and (2) "to continue to monitor CTV incidence in the three pest control districts, via an annual subsampling ("stat") survey of 10% of total acreage, randomly selected."

In response to the first objective, during the 1995–1996 fiscal year the CPL was addressed down to the 2.0% estimated infection level. During the 1996–97 fiscal year those groves that underwent tree removal during 1995–96 were rechecked. In addition, the CPL was further addressed down to the 1.3% estimated infection level. In fiscal year 1997–1998 "recheck" groves increased to include those in which tree removal occurred from 1995–1997, and the CPL was addressed down through the 1.0% estimated infection level.

As to the second objective, the overall disease incidence within the JPA Districts at the start of 1995, as estimated by the 1992–95 "stat" survey, was 0.316%. By February of 1998, at the conclusion of the 1997–98 monitoring "stat" survey, it had decreased to 0.167%.

The final component of the 1995–1998 Effective Plan called for evaluation, through scientific and constituent input, of the tree removal program. This evaluation began midway through the 1997–98 fiscal year. It was agreed that aggressive tree removal had proved successful in suppressing virus incidence. It was also agreed that because the systematic subsampling survey data had become outdated, and a new, more statistically accurate "hierarchical subsampling" method had been developed, there should be more balance between tree removal and resurvey. A maintenance plan was developed that emphasized a four–year systematic subsampling program, while continuing to address the CPL as resources allowed. At the conclusion of the four year systematic subsampling cycle, in the spring of 2002, the overall suspect infection rate had dropped further, to 0.120%.

Early in 2002, the maintenance plan was evaluated by both the Technical Advisory Committee (TAC) and the CCTEA Board, with input from the participating districts. As a result, the plan was revised, effective July 1, 2002. It included a five–year systematic subsampling program (covering 20% of acreage annually), with greater emphasis on CPL work.

2007 marked the end of the second cycle of a systematic subsampling of the participating districts using the Hierarchical Method. Once again the TAC and the CCTEA Board of Commissioners evaluated the Effective Maintenance Plan. It was clear that the most significant advantage to this plan was the detection of the use of illegal and/or inappropriate budwood sources. As these could have severely impacted adjacent growers and nurseries, it was agreed that a five–year cycle is most likely the uppermost limit between surveys. To make the most efficient use of limited financial resources, minor adjustments were made to the subsampling component of the Effective Plan. The new five–year cycle beginning in the 2007–2008 fiscal year differs from the previous protocol only in that not all groves within a TRS will be surveyed. Rather, each block of citrus is weighted based on past surveys, removals, and proximity to infected groves. The higher the risk of infection, the greater the chance the grove will be subsampled. Along with this modified subsampling survey, the program will continue to address the CPL as resources allow.

The Effective Maintenance Plan

Revision Effective July 1, 2007

The revised Effective Plan adopted by the CCTEA Board of Commissioners incorporates both the input of the TAC and the fiscal constraints of the participating pest control districts. The TAC continues to emphasize its support of the eradication of CTV–infected trees. Based on the continuous decrease in overall disease incidence, the TAC renewed its determination that the removal of CTV–infected trees is effective, and is the best known and accepted method for the control and eradication of CTV.

Plan Components

  1. Systematic Subsampling Survey
    Survey commercial citrus acreage over a five year period, targeting approximately 20 per cent of the Township—Range—Sections (TRS) containing citrus acreage in each District annually. Citrus blocks will be chosen for survey based on a selection process that weights each block based on past surveys, removals, and proximity to infected groves.
  2. Singles Survey (100% of grove)
    Continue to work toward the 0.0% infection level, using a semi–annually updated Collection Priority List.
  3. Titer Test Trees
    Monitor on a weekly basis the level of virus that can be detected in field trees.

Operational Details

  1. Systematic Subsampling Survey
    1. The TRS allocations will be the same as the 2002–2007 cycle with new acreage added, i.e., the sections subsampled in 2002–2003 (Year 1) will be those surveyed in 2007–2008, and so on. Prior to the fall, 2007 collection season, groves within each TRS will be assigned a weight factor based on past survey results, removals, and proximity to infected groves. The higher the risk of infection, the greater the chance a grove will be selected for subsampling.
    2. The Hierarchical (bulk) Sampling Method devised by Gottwald & Hughes will be utilized for the subsampling survey. Field verification trials, as well as implementation in the field from 1998 to the present, have indicated that this survey method is currently the most accurate available, especially in groves that have a low incidence of the virus. Because three leaves from each of four trees are pooled into one sample, the survey method will be used only when virus titer in field test trees consistently maintains an O.D. reading of 0.75 or higher.
  2. Singles Survey
    1. The Collection Priority List will continue to incorporate all sources of infection information, i.e., prior removals, systematic subsampling, etc. The CPL will be:
      1. based on the most recent survey results regardless of survey type;
      2. sorted by percent disease incidence, from highest to lowest; and
      3. updated semi–annually, incorporating all sources of survey results.
    2. Blocks on the CPL will be scheduled for singles collection (100% of the trees in a given grove), from the highest to lowest CTV incidence estimate, as resources allow.
    3. Sampling Methods:
      1. At virus titer consistently above 0.75, composite sampling will be conducted by combining two trees into one sample, 6 leaves per tree.
      2. At virus titer below 0.75, all sampling will be conducted according to an individual tree protocol (one tree per sample, 8 leaves per tree).
  3. Titer Trees
    1. The collection of test trees on a weekly basis will determine: 1) the correct times for the field department to start and stop field collection of tissue and 2) the type of survey method suitable for use.
      1. The Hierarchical Sampling Method may be used only when the titer is consistently above 0.75.
      2. Singles may be collected as composite samples only when the titer is consistently above 0.75. If the titer fluctuates below 0.75 but remains above 0.6, trees must be collected as single samples only. Tissue collection is not recommended when titer falls below 0.6 except under special circumstances.
    2. Wherever possible, a minimum of five trees per site will be sampled. Five sites, representative of the entire San Joaquin Valley, will be selected. However, it is recognized that with the majority of the infected trees having been removed from within the JPA Districts, it may be difficult to locate groves with a sufficient number of infected trees to monitor on a long term, weekly basis. Therefore,
      1. test trees may be limited to collections from within areas not practicing eradication (i. e., the Tulare County Pest Control District or the West Fresno County Red Scale Protective District); and/or
      2. it may be necessary to re–examine the level at which test trees are collected; that is, there may be collection from five trees within a whole TRS as opposed to within one individual grove.

Contact persons

Jill Barnier
Program Manager

Vic Corkins
Chair

22847 Road 140
Tulare, CA 93274

(559) 686-4973
(559) 686-5496


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