1. 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

2. 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.

3. Policy Relevance 1.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

4. 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%)

5. Price Cycle: California Fresh Strawberries (1988-2002)

6. 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

7. 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.

8. 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)

10. 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

11. 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

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

13. 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

14. 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

15. Damage Calculation

16. Marketable Value of Treated and Untreated Fall Planting: Watsonville Optimal sprays: end of Apr. & mid Aug.

17. 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

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

19. 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

20. 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.

21. 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.