a chemical resistant invader: greenhouse whitefly in strawberries colin a. carter, james a....
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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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Objectives1. 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 Relevance1. Policymakers need to understand how
producers will act to mitigate their losses not just pest biology
2. 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%
San Luis Obispo (5%)
Santa Barbara(10%)
Ventura (27%)
Orange (6%)
Monterey (33%)
Santa Cruz (18%)
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Price Cycle: California Fresh Strawberries (1988-2002)
0
0.5
1
1.5
2
2.5
0 5 10 15 20 25 30 35 40 45 50
Week
Fre
sh S
traw
berr
y P
rice
$/lb
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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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1500
2000
2500
3000
3500
4000
1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000
WF Days (Jan 29 - Jun 5)
Yie
ld (g
/ pl
ant)
y = -396.9Ln(x) + 5593.7
R2 = 0.46
Damage Calculation
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Marketable Value of Treated and Untreated Fall Planting: Watsonville
0.00.51.01.52.02.53.03.54.0
'000 $/acValue of BenchmarkYield per acreIncremental Value of2 spraysValue of 2 sprayyieldOptimal 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
-0.51.01.52.02.53.03.54.04.55.0
'000 $/ac Value of BenchmarkYield per acreIncremental value of 2spraysValue of 2 spray yield
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 Issues1. 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.