Research Article t Pheromone-based pest management can be cost-effective for walnut growers

by Kimberly P. Steinmann, Minghua Zhang, Joseph A. Grant, Carolyn Pickel and Rachael E. Goodhue

Many organophosphate and pyre- throid insecticides currently used by California walnut growers have been linked to negative environmental or human health impacts, increasing the probability of use restrictions and phase-outs. We assessed the accept- ability of alternative reduced-risk strategies by comparing their costs to those of pest management programs currently in use among San Joaquin County walnut growers. To do this, we analyzed data from the California Department of Pesticide Regula- tion’s legally mandated Pesticide Use Reports on actual pesticide applica- tions for 3 years, from 2002 to 2004. While many factors other than cost influence growers’ pest management choices, we found that alternative strategies can be cost-competitive with conventional approaches, de- pending on the pest pressure and savings due to reductions in second- ary pest outbreaks.

alifornia produces 99% of walnuts nationwide, and this commod- ityC is ranked 14th in the state with an Important pests of walnuts include codling moth, walnut husk fly, navel orangeworm, aphids and mites. Alternative, reduced-risk pest control strategies, annual value of $610 million (USDA such as pheromone “puffers” for codling moth (shown), were compared with 2006). The most important walnut pests strategies currently in use by walnut growers in the San Joaquin Valley. that can cause significant economic loss are codling moth (Cydia pomonella) However, many products frequently Food Quality Protection Act (FQPA) of and, in certain areas, walnut husk fly used by walnut growers are being re- 1996. In addition, nine of these 30 active (Rhagoletis completa). Webspinning mites evaluated for reduction or elimination ingredients are currently listed as im- (Tetranychus spp.) and aphids (primarily by regulatory bodies due to adverse pairing California water bodies under Chromaphis juglandicola) can also cause human health or environmental risks. the Clean Water Act of 1972, and more economic damage if not controlled by For example, 22 of the 30 active ingredi- are likely to be listed as water quality natural predators. The current manage- ents used to control walnut arthropod monitoring is extended to additional ment of these pests is based on periodic pests such as codling moth, walnut insecticides and miticides (US EPA 1997, treatments with organophosphates, husk fly, aphids and mites from 2002 2002; CDPR 2005). pyrethroids, growth-regulating insecti- to 2004 could be affected by proposed Because some of these pesticides are cides and miticides. changes stemming from the federal broad spectrum and have long residual

http://CaliforniaAgriculture.ucop.edu • July–September 2008 105 activity, they kill beneficial insects as costs of selected alternative strategies to well as the targeted pests. The loss of those of conventional strategies for con- beneficial insects can result in outbreaks trolling key pests of walnuts. of secondary pests such as mites and Conventional strategies and costs aphids, necessitating additional treat- ments and further increasing the poten- The first step in comparing the eco- tial for negative environmental impacts nomic feasibility of alternative and (Agnello et al. 2003; Prischmann et al. conventional strategies was to define 2005; Zalom et al. 2001). the specific products, use rates and Stemming from impending regu- application costs associated with each latory changes as well as growers’ strategy. To define conventional strate- heightened awareness of environmental gies, we used actual grower data from and worker safety, new technologies the California Department of Pesticide have emerged in the form of alterna- Regulation’s Pesticide Use Reports tive, lower risk products for controlling (PUR), a public database of legally arthropods. These include pheromone mandated pesticide application reports mating disruption, biopesticides and (CDPR 2005). The PUR database offers a growth-regulating insecticides. Mating wealth of information about California disruption works through the inun- growers’ pesticide use, including ac- dation of an orchard with synthetic tive ingredients, amount per acre ap- chemicals designed to mimic phero- plied and number of applications per mones that are released by females to season. This allowed us to compile attract males of a species, thus decreas- comprehensive, detailed and accurate ing the male’s ability to locate a female representations of individual grower’s and successfully mate. Biopesticides pest management strategies based on Integrated pest management, along with new technologies such as pheromone are microbial and biochemical controls reported pesticide use in the study area. mating disruption, biopesticides and with microorganisms naturally antago- We analyzed PUR data for walnut or- growth-regulating insecticides, help to nistic toward pests, while insect growth chards in San Joaquin County for 2002 protect farmworkers and the environment. Retired Butte County farm advisor Bill Olson regulators disrupt hormone functions through 2004. San Joaquin County is monitors for codling moth by hanging traps responsible for molting, maturation California’s leading walnut-producing in walnut orchards. and other insect life-cycle processes. county, with just under 32,000 acres of Although varying in their modes of ac- orchards accounting for about 16% of tion, these new, narrow-spectrum alter- the annual walnut crop value statewide natives selectively control pests and are (CASS 2004). From 2002 to 2004, 372 to less disruptive to beneficial insects and 384 San Joaquin County walnut grow- 3 years, depending on whether they mites. Many of these new approaches ers reported pesticide use in the PUR treated for codling moth in a given also reduce the risk that orchard pesti- database (CDPR 2005). year. As a result, there were approxi- cide applications will adversely affect For each of the 3 years studied, we mately 220 pest management strategies wildlife, water quality and human created a subset of the PUR database analyzed each year, with a total of 661 health (US EPA 2006). that included only those growers who strategies over the 3 years combined. Recent studies have documented the appeared to have treated solely for We calculated the costs of conven- effectiveness of certain alternative strat- codling moth, or for codling moth plus tional strategies reported in the PUR egies for controlling codling moth and other pests, based on product choice database using the amounts of product walnut husk fly in walnuts (Coates et al. and timing criteria. Codling moth was applied per acre and their 2003 prices, 2001; Flora et al. 1999; Pickel et al. 2007; the focal pest for defining the proj- and adding a standardized cost for each Van Steenwyk et al. 2005), and growers ect’s PUR subset for analysis, given application in a treatment that covered have begun integrating some of these its economic importance as a walnut fuel, labor and maintenance. We as- approaches into their orchard manage- pest and the promise of pheromone sumed that all pesticide applications ment programs. However, alternative mating disruption as an effective con- were made by a conventional orchard approaches may be more expensive due trol. However, for each grower in the air-blast sprayer. Multiple pesticides to an increased number of applications, subset, the grower’s pest management reported by a grower on the same date higher material costs, a greater time strategy was defined as all of the ar- and same acreage were assumed to be commitment for orchard pest monitor- thropod pest controls used throughout combined into a single “tank mix” ap- ing, and lower numbers of pest species the entire season on all orchards listed plication. All insecticide and miticide controlled per application. Because under a grower’s PUR identification costs were then summed to arrive at growers will not broadly adopt alterna- number. Therefore, the pest manage- a total pest-management strategy cost tive technologies unless they are effec- ment strategies of a single grower per acre for each grower’s conventional tive and economical, we compared the could have been included for 1, 2 or all strategy in each year.

106 CALIFORNIA AGRICULTURE • VOLUME 62, NUMBER 3 Sarah Goldman Smith

TABLE 1. Average annual conventional pest-management strategy costs of San Joaquin County walnut grower sample

Grower Strategies Average chemical class analyzed cost/acre* no. (average/yr.) $ Combination 262 (87) 160 a† Organophosphate 350 (117) 124 b Pyrethroid 49 (16) 73 c All classes 661 (220) 134 * Data pooled over the 3 years (insignificant effect of year on cost). † Means in columns with different letters differ (P < 0.05), least squares mean test with square-root transformation to meet normality and homogeneity of variance assumptions.

We compared costs for the entire While many walnut growers are trying out alternative pest-control strategies, the analysis subset of pest management strategies of California Pesticide Use Reports from 2002 to 2004 found that actual adoption rates in the PUR database for a given year, are low. Left to right, Rick Enos of Carriere Farms, Tom Larsen of Suterra, Bill Carriere, as well as divided the subset into three Christine Abbott of Suterra and Glenn County farm advisor Bill Krueger learned about pheromone puffers at Carriere Farms in Glenn County. groups based on the predominant chemical class of FQPA-targeted insec- ticides used to control codling moth, organophosphate at $124 per acre and that of conventional pesticides (Pickel aphids and walnut husk fly: organo- pyrethroid at $73 per acre. et al. 2007). For orchards with severe phosphate, pyrethroid or a combination codling moth infestations, one or Alternative strategies and costs of the two. Therefore, while a single more supplemental insecticide appli- grower could potentially contribute up Based on recent research and the cations may be necessary to achieve to three pest-management strategies to advice of experts, we created alterna- control comparable to that of conven- the analysis, the chemical class could tive pest-management strategies that are tional spray programs. We created vary annually, depending on the grow- both low environmental risk and con- and analyzed two pheromone-based er’s product choice in a given year. sidered effective for controlling codling alternative strategies judged capable Combining the 3 years studied, 53% moth, aphids and walnut husk fly at lev- of providing control under varying of all growers’ pest management strat- els commonly encountered in the study degrees of codling moth pressure: one egies were classified as organophos- area (table 2). All the strategies were in which pheromone puffers were the phate, 7% were pyrethroid and 40% based on the control of codling moth only method of control, and another of were combinations of the two (350, 49 using pheromone mating disruption puffers plus a single supplemental ap- and 262 strategies, respectively). Control (E,E,-8,10-Dodecadien-1-ol) dispensed plication of the insect growth regulator costs varied widely within each group with bulk aerosol “puffers,” which methoxyfenozide (Intrepid). depending on the products used, their saturate the orchard atmosphere with Both alternative strategies also rates and the number of applications pheromone for up to 180 days through included a single application of chlor- per season, but there were significant regularly timed releases (Suterra, LLC). pyrifos (Lorsban) to control aphids. differences among the groups’ total Recent research has shown that in Chlorpyrifos is an organophosphate of costs (table 1). Combination strategies orchards with low or moderate popula- regulatory concern, but there were no had the highest average annual con- tions, pheromone puffers can provide effective reduced-risk products avail- trol costs at $160 per acre, followed by control of codling moth equivalent to able for controlling aphids in walnuts at

TABLE 2. Alternative strategies to control codling moth, aphids and walnut husk fly

Alternative strategy Sprays Codling moth Aphid Walnut husk fly Cost per acre no. $ Low codling moth pressure and no husk fly 1 Pheromone puffer Chlorpyrifos 108 Puffer installation labor (Lorsban 4E) Low codling moth pressure and husk fly 3 Pheromone puffer Chlorpyrifos Spinosad (Success) 193 Puffer installation labor Corn gluten meal (NuLure) High codling moth pressure and no husk fly 2 Pheromone puffer Chlorpyrifos 164 Puffer installation labor Methoxyfenozide (Intrepid 2F) High codling moth pressure and husk fly 4 Pheromone puffer Chlorpyrifos Spinosad 248 Puffer installation labor Corn gluten meal (NuLure) Methoxyfenozide

http://CaliforniaAgriculture.ucop.edu • July–September 2008 107 The alternative strategies compare favorably in cost to conventional strategies currently in use by a large portion of walnut growers in the study area. the time of the study. The chlorpyrifos rate used for our alternative strategies TABLE 3. Products, rates, prices and application number for alternative strategies is adequate to provide good control of aphids while reducing the risks of disrupting biological control in the or- Applications Control Application rate Price per season chard, as well as off-site environmental no. or amount/acre $ no. effects. To control walnut husk fly (in Puffer (pheromone) 1 (per 2 acres) 120/puffer 1 addition to codling moth), our alterna- Methoxyfenozide (Intrepid 2F) 1 pint 40/pint 1 tive strategies included two alternate- Chlorpyrifos (Lorsban 4E) 4 pints 5.59/pint 1 row applications of spinosad (Success), Spinosad (Success) 0.2 pint 105.75/pint 2 a selective microbial insecticide, along Corn gluten meal (NuLure) 3 pints 2.99/pint 3 Labor for puffer installation 10/acre 1 with a feeding-attractant corn gluten Orchard sprayer application* 15.57/application 1–4 meal bait (NuLure). This bait was also in- * Assumed equal for all growers (Buchner et al. 2002). cluded with the chlorpyrifos application for aphids, so as to attract walnut husk fly and allow chlorpyrifos to simultane- insect growth regulator methoxyfenoz- fly, we assessed three possible mite ously serve as both a walnut husk fly and ide was also required to control codling management outcomes: aphid control. Navel orangeworm was moth effectively. (1) Eliminated. Biological control not analyzed because its life cycle did not Walnut husk fly treatments in our al- maintains mites below economically significantly overlap with codling moth’s, ternative strategies were applied to ev- damaging levels; grower’s miticide and most growers in the county did not ery other tree row, based on the results costs, per the PUR database, were not consider it an important pest. of recent efficacy studies (Van Steenwyk added to the costs of the alternative et al. 2005). The calculated costs of four strategies. Study assumptions alternative strategies for controlling (2) Reduced. The narrow-spectrum Although the PUR does not require codling moth and aphid alone — or nature of the alternative strategy al- growers to report what pests a pesti- codling moth, aphid and walnut husk lowed for some improvement in biologi- cide application is meant to control, fly — ranged from $108 to $248 per acre, cal mite control; half of the grower’s we inferred which pests were targeted depending on codling moth pressure reported miticide costs were added to based on the product used, time of ap- and other target pests (tables 2 and 3). the costs of the alternative strategies. plication, advice of experts and results Mite controls were not included in (3) Unchanged. The use of alternatives of a 2005 survey of San Joaquin walnut these hypothetical alternative-strategy had no effect on mites; all of the grower’s growers about their specific problem cost values, so that they could be added reported miticide costs were added to pests and the products they use to con- selectively based on varying biological the costs of the alternative strategies. trol these pests (Steinmann et al., un- control effectiveness assumptions. Economic feasibility published). Because growers sometimes Mite control use the same materials and application While many factors influence grow- timings for controlling codling moth In a variety of field and orchard ers’ choices of pest management strate- and aphids, treatments for these pests crops, broad-spectrum insecticides may gies, we chose to assess the feasibility of could not be distinguished from one disrupt the biological control of mites, alternative over conventional strategies another in our analysis. All growers triggering secondary mite outbreaks by comparing their costs. To estimate were therefore assumed to control for that necessitate further pesticide use the share of growers who would con- aphids as well as codling moth. (Agnello et al. 2003; Prischmann et sider an alternative strategy economi- Similarly, we could not determine if al. 2005; Zalom et al. 2001). In many cally feasible, we proposed that growers a grower had high or low codling moth instances, substituting more-selective would adopt the strategy if its cost was pressure based on the PUR data. Given insecticides has helped reduce the se- equal to or less than that of their cur- the focus of this paper on codling moth verity of these secondary mite infesta- rent conventional strategy. Using this and pheromone mating disruption, tions and in turn the overall costs of criterion for economic feasibility, we we decided to assess the sensitivity of managing orchard pests. While such calculated the percentages of growers’ our results to codling moth pressure effects have neither been confirmed nor pest management strategies for which by running the analysis under two ruled out for walnuts so far, reductions costs are greater than or equal to that blanket assumptions. The first analysis in mite control costs could significantly of the various alternative strategies. assumed that all growers have a low-to- increase the economic feasibility of al- The implication is that these alterna- moderate codling moth pressure, and ternative approaches. tive strategies would be economically therefore puffers were enough to con- To predict how reduced miticide use feasible for controlling codling moth, trol codling moth. The second analysis would affect the economic feasibility of aphid, mite and walnut husk fly under assumed that all growers have high cod- our alternative strategies for controlling matching presence and abundance of ling moth pressure, and therefore the codling moth, aphid and walnut husk these pests in their orchards.

108 CALIFORNIA AGRICULTURE • VOLUME 62, NUMBER 3 TABLE 4. Percentage of pest management strategies in each chemical class with costs greater than or lower cost than conventional strategies equal to costs of alternative strategies with varying levels of reduction in mite control costs to be acceptable, but growers may elect to use alternative strategies even if they Mite control costs are more costly than conventional ap- Chemical class Eliminated Reduced Unchanged proaches...... % ...... For example, in a 2002 survey of San Low-to-moderate codling moth pressure Joaquin County walnut growers by the Combination 62 48 25 Organophosphate 52 31 16 UC Sustainable Agriculture Research Pyrethroid 12 8 4 and Education Program (SAREP), 56% All classes 53 36 19 of 299 respondents agreed “somewhat High codling moth pressure to strongly” with the statemen, “It’s Combination 19 7 4 worth using practices that reduce my Organophosphate 7 3 1 overall chemical use even when it might Pyrethroid 2 0 0 take a little more expense” (Beverly All classes 12 4 2 Ransom et al., unpublished). Similarly, a 1999 analysis of U.S. Midwestern corn Under the best-case scenario with of the miticide costs could be saved, only and soybean farmers showed that they low-to-moderate codling moth pres- 48% of combination strategies, 31% of would be willing to pay an average of sure, coupled with no secondary pest organophosphate strategies and 8% of $8.25 per acre more for alternative farm- mite infestation, the pest control costs pyrethroid strategies had costs greater ing practices that reduced risks to the for 53% of the reported pest manage- than or equal to those of the alternative environment (Lohr et al. 1999). The rea- ment strategies were greater than or strategies. When mite control costs were sons for such willingness may include equal to the cost of the associated alter- unchanged, these figures dropped fur- real or perceived reductions in risks native strategy (table 4). Breaking the ther to 25%, 16% and 4%, respectively. to worker health, orchard ecology or conventional strategies down by chemi- Finally, for high codling moth pres- the environment, and the proximity of cal class, we found that costs were sure, adding half of mite control costs the farming operation to urban areas, greater than or equal to the alternative dropped the alternative strategies’ homes and schools. strategy for 62% of those that combined economic feasibility from 12% to 4%. Low adoption rates organophosphate and pyrethroid, 52% When full mite control costs were in- of organophosphate strategies and 12% cluded, economic feasibility dropped Our analysis of PUR-reported pes- of pyrethroid strategies. even further to only 2%. When miticide ticide use showed that many growers However, under the assumption of costs were reduced by half, 7%, 3% and have not adopted alternative pest- high codling moth pressure requiring 0% of combination, organophosphate management strategies despite their a supplemental insecticide application, and pyrethroid strategies, respectively, willingness to incur slightly higher costs coupled with no secondary pest mite had costs greater than or equal to those when surveyed in 2002. Over the 3 years infestation, only 12% of the conven- of alternative strategies. When miticide of our study, for example, only 13% to tional pest-control strategies were more costs remained unchanged, these fig- 17% of growers used at least one applica- costly than or equal to the alternative ures were 4%, 1% and 0%, respectively. tion of an alternative product during the strategies. Again, breaking the con- In three important respects, our al- growing season. Of these growers, 58% ventional strategies down by chemical ternative strategies were constructed to 63% used more than one application class, costs were greater than or equal conservatively and, as such, may be of broad-spectrum insecticide in addi- to the alternative strategies for 19% of more acceptable among walnut growers combination strategies, 7% of organo- than our findings indicate. First, recent phosphate strategies and only 2% of findings from large-scale pheromone pyrethroid strategies. puffer trials in walnuts suggest that Clark Kelly Jack The feasibility of alternative strategies repeated use over several years can re- also dropped when we added half or duce codling moth to acceptable levels all of PUR-derived mite control costs to even in orchards with high populations reflect poorer biological control of these (Pickel et al. 2007). Second, we assumed pests. With low codling moth pressure, that all growers use a low-dose applica- adding half of the reported mite control tion of chlorpyrifos to control aphids, costs reduced the economic feasibility but not all orchards are treated for of the alternative strategies from 53% aphids each year. In a 2006 survey of to 36%. When all of the reported mite- San Joaquin County walnut growers, control costs were added, the alternative for example, only 48% of respondents strategies’ economic feasibility dropped reported treating for aphids (Steinmann even further to 19%. When codling moth et al., unpublished). Third, we assumed Codling moth (adult, shown) is a major pest pressure was low-to-moderate and half that alternatives must have an equal or of walnuts and other orchard crops.

http://CaliforniaAgriculture.ucop.edu • July–September 2008 109 tion to the alternative products. Only 5% and unchanged miticide costs, the use is beneficial to growers, consumers and to 7% had strategies that included broad- of FQPA-targeted pesticides would be the environment. spectrum materials at lower rates that reduced by around 6%. were roughly equivalent to those used in These results open new doors to- K.P. Steinmann is Graduate Student, and M. our alternative strategies. ward potential areas of study that can Zhang is Associate Professor, Department of Land, There are many possible reasons for foster improvements in many already- Air and Water Resources, UC Davis; J.A. Grant is the low rate of adoption among grow- existing alternative pest controls. As Farm Advisor, UC Cooperative Extension (UCCE), ers, including lack of familiarity, higher research continues to unveil the interac- San Joaquin County; C. Pickel is Integrated Pest material costs, risk of lower yields and tive dynamics of pests, natural preda- Management Advisor, UCCE Sutter/Yuba coun- ties; and R.E. Goodhue is Associate Professor, De- revenues due to lower efficacy, and new tors and their orchard environment, as partment of Agricultural and Resource Economics, requirements for increased monitoring well as new ways to manipulate these UC Davis. We gratefully acknowledge the sub- and attention to the timing of applica- interactions, there is great potential for stantive contributions to this article of Associate tions. Our results suggest that the alter- increasing the use of existing reduced- Editor Karen Klonsky, Cooperative Extension Spe- native strategies we analyzed compare risk products and for the development cialist, Department of Agricultural and Resource favorably in cost to conventional strate- of new ones. Although many unknowns Economics, UC Davis. We also thank Richard gies currently in use by a large portion remain, our analysis suggests that alter- DeMoura for his great help in acquiring data and Richard Buchner for help in early stages of the of walnut growers in the study area, native, narrow-spectrum pest control project. This project was funded by the Proposi- dependent on the effectiveness of biologi- strategies such as pheromone puffers tion 50 Agricultural Water Quality Grant Program, cal control. The highest percentages of may be both economically and environ- Agreement No. 04-318-555-0, and U.S. EPA conventional pest-management strategies mentally viable in the long run, contribut- Region 9, Strategic Agriculture Initiative Program, that could be most feasibly replaced by ing to sustainable walnut production that Assistance ID Number X8-97964701-0. an alternative strategy appear to be those employing a combination of organophos- phates and pyrethroids throughout the References Pickel C, Grant JA, Welter SC, et al. 2007. Using aero- season, followed by those using predomi- Agnello AM, Reissig WH, Kovach J, Nyrop JP. 2003. sol pheromone “puffers” for area-wide suppression Integrated apple pest management in New York State of codling moth in walnuts: Year 2 and demonstra- nantly organophosphates. using predatory mites and selective pesticides. Ag Eco- tion of aerially applied pheromone laminate flakes. Due to their low cost, pyrethroid sys Env 94:183–95. California Walnut Marketing Board Research Reports 2006. Sacramento, CA. http://walnutresearch.ucdavis. strategies would be the least likely to be Belden JB, Lydy MJ. 2006. Joint toxicity of chlorpyrifos edu/2006/2006_137.pdf. p 137–53. replaced by alternative strategies. The and esfenvalerate to fathead minnows and midge lar- low cost and high efficacy of pyrethroid vae. Env Toxicol Chem 25(2):623–9. Prischmann DA, James DG, Wright LC, et al. 2005. Effects of chlorpyrifos and sulfur on spider mites (Ac- insecticides, in conjunction with the Brun-Barale A, Bouvier JC, Pauron D, et al. 2005. In- ari: Tetranychidae) and their natural enemies. Biologic current regulatory focus on restrict- volvement of a sodium channel mutation in pyrethroid Control 33:324–34. resistance in Cydia pomonella L, and development of a ing the use of organophosphates, have diagnostic test. Pest Manage Sci 61:549–54. [USDA] US Department of Agriculture. 2006. Sum- made pyrethroids an attractive option mary of County Agricultural Commissioner’s Reports, Buchner RP, Edstrom JP, Hasey JK, et al. 2002. Sample 2004–2005, National Agricultural Statistics Service, for growers. However, the future avail- Costs to Establish a Walnut Orchard and Produce California Field Office, Sacramento, CA. www.nass. ability of pyrethroids is threatened Walnuts, Sacramento Valley, Sprinkler Irrigated. UC usda.gov/Statistics_by_State/California/Publications/ by recent studies on the adverse envi- Cooperative Extension. WN-SV-02 http://coststudies. AgComm/200508cavtb00.pdf. ucdavis.edu/files/walnutsac2002.pdf. 19 p. ronmental impacts of these materials [US EPA] US Environmental Protection Agency. 1997. and on the risk that increased use may [CASS] California Agricultural Statistics Service. 2004. Federal Register. 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Sacramento, CA. http://walnutresearch. and Disease Management Conf. Washington State ucdavis.edu/2004/2004_159.pdf. p 159–78. tive strategy of low-to-moderate cod- Univ, Portland, OR. http://entomology.tfrec.wsu.edu/ ling moth pressure and the complete wopdmc/1999PDF/4-Chemical/Chemical%2099-23. Zalom FG, Stimmann MW, Arndt TS, et al. 2001. elimination of miticides, this rate could pdf. p 79–81. Analysis of permethrin (cis- and trans-isomers) and esfenvalerate on almond twigs and effects of residues be reduced by 43% to 2.13 pounds per Lohr L, Park T, Higley L. 1999. Farmer risk assessment for on the predator mite Galendromus occidentalis (Acari: acre. Even under the worst-case sce- voluntary insecticide reduction. Ecol Econ 30:121–30. Phytoseiidae). Env Entomol 30(1):70–5. nario of high codling moth pressure

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