A Chemical Resistant Invader: Greenhouse Whitefly in Strawberries

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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

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Objectives

1. Measure impact of greenhouse whitefly on
   strawberry yields (damage calculation).
2. Incorporate environmental regulations regarding
   chemical use.
3. Account for commodity price cycle.
4. Develop a simple action threshold model to
   identify optimal chemical treatment dates.
5. Evaluate how control based on private incentives
   contributes to regional management of pest.

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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

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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)
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Price Cycle California Fresh Strawberries
(1988-2002)
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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

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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.

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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)

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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

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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

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Source Dr. Tom Perring, UCR
Source Dr. Nick Toscano, UCR - 1999
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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

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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

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Damage Calculation
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Marketable Value of Treated and Untreated Fall
Planting Watsonville
Optimal sprays end of Apr. mid Aug.
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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

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Marketable Value of Treated and Untreated Fall
Planting, Oxnard CA
Optimal sprays early Jan mid April
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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

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Other Issues

1. Dynamic considerations may matter less when total
   applications limited. Also, reinfestations from
   neighboring crops breaks the link between your
   actions now whitefly population later.
2. Does market power make a shipper less concerned
   (risk preferences and also more inelastic
   demand).
3. Optimization errors by producers.

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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.