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Fruit Notes |
Residues of Azinphosmethyl on
Apples Using |
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Fruit Notes |
Starker Wright and Ronald
Prokopy |
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Fruit Notes |
Over the past two decades, we have attempted to develop an alternative behavioral approach to AMF control. This approach involves surrounding an orchard block with odor-baited red spheres placed about 5 yards apart on perimeter trees. Each sphere is either coated with Tangletrap or is treated with a feeding stimulant and an insecticide to kill alighting flies [Fruit Notes 62(4)]. Ideally, this system of management would allow the grower to cease insecticide application after plum curculio season, in effect extending the pre-harvest interval for summer insecticide use to 80 days or more. One grower-perceived advantage to behavioral control of AMF is reduction in use of summer insecticides and subsequent reduction in level of insecticide residue on fruit at harvest [Fruit Notes 60(4)]. The EPA sets standards for commercially acceptable levels of pesticide residue on marketed fruit. Currently, the standard for azinphosmethyl residue on apples is 2 parts per million (2000 parts per billion). However, the Food Quality Protection Act (FQPA) may strongly affect tolerable levels of residue. The intent of the FQPA is to establish tolerance levels that are safe, defined as a reasonable certainty that no harm will result from aggregate exposure, including all exposure from diet, drinking water, and other non-occupational exposures. In order to calculate health risks associated with exposure to pesticide residues, the FQPA dictates that aggregate exposure be measured by use of a risk cup, meaning that all exposures (fresh and processed foods, water, and household exposure) are combined into the same cup. All existing tolerances must be re-evaluated, and organophosphate insecticides (such as azinphosmethyl) are included in the first round of review, slated for completion in August of 1999. Tolerance levels are based on residues present on fruit at harvest. Our aim here was to determine the amount of azinphosmethyl on fruit at harvest in blocks of apple trees that received azinphosmethyl for AMF control versus blocks that received only odor-baited red spheres for AMF control. Materials & Methods In 1997, we began a pilot third-level IPM project in order to determine the influence of apple tree architecture and planting density on biologically-based pest management and fruit quality. In each of eight commercial orchards, we identified and flagged six blocks of trees: two each of high, medium, and low tree density. One block of each density was managed under first-level IPM practices that involved application of two to four sprays of insecticide from early July to harvest. The other block was managed under third-level practices that involved surrounding the block with odor-baited red spheres. For purposes here, fruit were sampled only from the medium-density trees, which, at ~240 trees/acre, represent the majority of apple trees in Massachusetts. Of the eight medium-density third-level IPM blocks and the eight companion first-level blocks, five pairs were selected for sampling here. Selection was based on the fact that azinphosmethyl was the insecticide applied against AMF in all five first-level blocks. Within one week of harvest, ten mid-sized McIntosh fruit were selected randomly from each block, bagged, and placed within 6 hours in a deep-freeze at ?20oC until the analyses were performed. Fruit fortified with known levels of azinphosmethyl showed that there is no significant breakdown of residues while in storage. From each experimental block, three samples were analyzed, each sample consisting of three fruit. For analysis details, see the note at the end of the text. Results In the five blocks under first-level IPM, growers used an average of 2.4 sprays against AMF between early July and late August, resulting in an average of 0.2% AMF injury (Table 1). Analysis revealed that fruit treated with 2-3 sprays of azinphosmethyl contained an average of 95.6 parts per billion of azinphosmethyl residue at harvest, roughly 5% of the current EPA tolerance. In keeping with the principles of behaviorally-based AMF control, no insecticides were applied to the five third-level IPM blocks after mid-June. Expectedly, none of the samples taken from these blocks contained a detectable level of azinphosmethyl residue, even though these blocks received an average of 2.8 applications of azinphosmethyl against plum curculio in May and June (Table 1). Blocks managed under third-level practices received slightly more injury by AMF (0.4%) than did first-level blocks. Conclusions This study has shown that the amount of azinphosmethyl residue present on apples at harvest in 1997 in test blocks managed under first-level IPM practices averaged far less (about 95% less) than the amount of residue allowed by current EPA regulations. This study also showed that no detectable residues of azinphosmethyl were found on apples at harvest in test blocks managed under third-level IPM practices. Although it may seem logical that no insecticide treatment during July and August (as under third-level IPM) ought to result in no insecticide residue on fruit at harvest, such would not necessarily be the case if insecticide applied against plum curculio were to be present on harvested fruit. All ten blocks in this study received two to four sprays of azinphosmethyl from mid-May to late June against plum curculio. Our data from fruit samples taken in third-level IPM blocks clearly show that treatments of azinphosmethyl applied in May and June did not result in detectable levels of azinphosmethyl on harvested fruit (Table 1). This information could be important to EPA consideration of continued allowable use of azinphosmethyl against plum curculio. Even though our findings here indicate that use of third-level IPM practices results in no detectable residues of azinphosmethyl on fruit at harvest and provides acceptable commercial-level control of AMF, more work is needed to refine third-level IPM practices so that they will become as economical and reliable as first-level IPM practices. Acknowledgments This work was supported by state/federal IPM funds and USDA SEA CSREES Grant # 97-34365-5043. We are grateful to the eight growers that participated in this study: Bill Broderick, David Chandler, David Cheney, Dana Clark, David Shearer, Joe Sincuk, Tim Smith, and Mo Tougas. Note: Whole fruit were blended with water and submitted to extraction with ethyl acetate, then reduced using a sample concentrator, leaving a concentrate of residual material. Azinphosmethyl residues from extracted apples were analyzed using a Varian model 3400 GC gas chromatograph (Varian Associates, Sunnyvale, CA) equipped with a nitrogen phosphorous detector (NPD). The capillary column was a fused silica DB-5 liquid phase, 0.53 mm i.d. X 15 m, 0.25mm film thickness (J & W Scientific). A deactivated cyclodouble-gooseneck injection port liner (Restek, Bellefonte, PA) was used for splitless injections. Operating conditions were as follows: injection volume, 1.0 ml; injection port temperature, 250oC; detector temperature, 300oC; column temperature, 175oC for 0.5 min, ramped at 20oC/min to 250oC and held for 12 min. The carrier gas was helium at a rate of 8 ml min-1. Detector gas flow rates were: nitrogen, 25 ml min-1; oxygen, 175 ml min-1; hydrogen, 2.5 ml min-1 (Kadenczki et al., J. Assoc. Off. Anal. Chem. 75, No.1, 53-61). |
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