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A Chemical Resistant Invader: Greenhouse Whitefly in Strawberries. Colin A. Carter, James A. Chalfant, Rachael E. Goodhue, & Greg McKee University of California-Davis PREISM Workshop, Aug. 2004. Objectives. Measure impact of greenhouse whitefly on strawberry yields (damage calculation).

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a chemical resistant invader greenhouse whitefly in strawberries

A Chemical Resistant Invader: Greenhouse Whitefly in Strawberries

Colin A. Carter, James A. Chalfant, Rachael E. Goodhue, & Greg McKee

University of California-Davis

PREISM Workshop, Aug. 2004

objectives
Objectives
  • Measure impact of greenhouse whitefly on strawberry yields (damage calculation).
  • Incorporate environmental regulations regarding chemical use.
  • Account for commodity price cycle.
  • Develop a simple action threshold model to identify optimal chemical treatment dates.
  • Evaluate how control based on private incentives contributes to regional management of pest.
policy relevance
Policy Relevance
  • Policymakers need to understand how producers will act to mitigate their losses

 not just pest biology

  • Key Players:

EPA

CA Dept. of Pesticide Regulation (DPR)

CA Strawberry Commission & Industry

Calif. Dept. of Food and Agriculture

california strawberries
California Strawberries
  • Coastal production
  • California accounts for over 80% of U.S. production
  • Florida accounts for around 12%

Santa Cruz (18%)

Monterey (33%)

San Luis Obispo (5%)

Ventura (27%)

Santa Barbara

(10%)

Orange (6%)

traditional season
Traditional Season
  • Fall planting (90% of acreage)
    • Planted late Sept. (Oxnard) – Oct. (Watsonville)
    • Harvested
      • December – June in Oxnard area
      • March – October in Watsonville area
  • Summer planting (10% of acreage)
    • Planted in July (Oxnard) & August (Watsonville)
    • Harvested
      • September – December in Oxnard area
      • October – May in the Watsonville area
calif industry has closed the southern hemisphere window
Calif. Industry Has Closed the Southern Hemisphere Window
  • CA Strawberries are now available essentially year-round: no more from Australia/NZ.
  • Did growers inadvertently also provide a host for whiteflies year-round?
  • Southern Calif: filled gap in season for whitefly.
  • Northern Calif: provided convenient, better host late in year.
greenhouse whitefly resident invader
Greenhouse Whitefly: Resident Invader
  • Common pest along CA coast
  • Emerged in strawberries in 1999-2000
    • Strawberries not previously a host
    • Invaded primarily Oxnard and Watsonville areas
    • Heavy infestation in 2002
  • Possible explanations for invasion:
    • Increased summer acreage
    • Expansion of total acreage
    • Urban hosts closer to strawberry fields
    • Nursery stock (Oxnard)
economic impact of whitefly
Economic Impact of Whitefly

Feeds on the sap of strawberry plant

  • Reduce total yield up to 25%
  • Reduce marketable yield
  • Decrease nutritional content (less sugar, citric acid)
  • Helps spread plant viruses
greenhouse whitefly management
Greenhouse Whitefly Management
  • Control is complicated
    • Difficult to kill (resistant to traditional chemicals)
    • Feeds on underside of leaf
  • Few chemical products registered for control
    • Admire (used at planting): not registered
    • Esteem: not registered
    • Other chems. provide limited control of adults
  • Eliminating plant hosts is another option
    • Crop clean-up
    • Reducing overlap of strawberry plantings
    • Break continuous whitefly cycle by eliminating plant hosts
slide12

Source: Dr. Tom Perring, UCR

Source: Dr. Nick Toscano, UCR - 1999

economic issues
Economic issues
  • Price cycle creates economic incentive to plant “host” crops
  • Continuous “host” plants allows year-round population development
    • Summer plantings
    • Second year plantings
    • Late harvest for processing
    • Alternative hosts (Oxnard)
  • Lack of grower coordination in whitefly management
  • Environmental regulations of chemical control
esteem pyriproxyfen
Esteem (pyriproxyfen)
  • Esteem provides effective post-plant whitefly control
    • Application costs approx. $40/acre
    • Effective for up to nine weeks
    • Sometimes used in conjunction with Admire (Imidacloprid)
    • Emergency registration for 2004
    • Restricted to two applications per acre per year
slide16

Marketable Value of Treated and Untreated Fall Planting: Watsonville

Optimal sprays: end of Apr. & mid Aug.

comments on watsonville case
Comments on Watsonville Case
  • WF population peaks in March – April
  • Late April Esteem spray may not fully control Whitefly population
    • Likely to promote larger overall population
    • Watsonville monoculture
  • August spray reduces carryover into fall plants, transplanted in Oct– Nov
slide18

Marketable Value of Treated and Untreated Fall Planting, Oxnard CA

Optimal sprays: early Jan & mid April

comments on oxnard model
Comments on Oxnard Model
  • WF population peaks in late March – April
  • Spray in March or April will control the historical spike in WF population
  • If only fall plantings, entire harvest season could be protected
    • Increasing summer acreage makes this unlikely
    • Multiple hosts makes reinfestation likely
other issues
Other Issues
  • Dynamic considerations may matter less when total applications limited. Also, reinfestations from neighboring crops breaks the link between your actions now & whitefly population later.
  • Does market power make a shipper less concerned (risk preferences and also more inelastic demand).
  • Optimization errors by producers.
conclusion
Conclusion
  • If growers focus on the value of strawberries instead of the number of whiteflies, this delays the first spray of Esteem until April & may not result in total whitefly control in the Watsonville area.
  • Significance: individual grower spray decisions may not completely control the greenhouse whitefly, and the severity of the invasion could worsen.