Franklin R. Hall

Initial behavioural responses of Aphis gossypii to defined deposits of bifenthrin on chrysanthemum

Abstract Uniformly sized droplets (60–160 μm in-flight diameter) of bifenthrin were applied to the abaxial surface of portions of chrysanthemum leaves. Adult Aphis gossypii were exposed to the freshly dried deposits and their activity during the next 20 min was video-taped using a camera placed beneath the treated area. On unsprayed or water-sprayed control leaves very little movement was recorded (mean distance walked ∼0·5 cm aphid−1) but aphids walked >2·0 cm during the exposure period in response to particular combinations of droplet size, droplet density and concentration of active ingredient (a.i.). Records of distance walked described the data satisfactorily, in most cases, when regression analysis was performed to show the effect of changing droplet density at each drop size and concentration combination. However, the description was improved when the number of aphids that moved during the experimental period, and the number that walked or dropped off the treated area, were also used to derive an irritancy index. Using this index, it was established that the irritancy was not dose dependent as a 50-fold range in quantity of a.i. cm−2 elicited the same response when presented to the aphids in deposits of different quality. However, there was some evidence for a minimum effective dose at the lowest concentration. The implications of these data are discussed in relation to the dose transfer process and the longer-term effects of sub-lethal behavioural responses.

Contribution of aerosols generated during mixing and loading of pesticides to operator inhalation exposure.

The occupational exposure resulting from the application of crop protection agents continues to be of great interest for the purposes of identifying hazards or determining safer chemical handling methods. The purpose of the present study was to identify the potential respirator exposure of a mixer/loader to chlorothalonil, with the mixing and loading operation as the only source of aerosols (particles <13 microm diameter). Three worst-case mixing/loading scenarios were simulated in the lab: (1) a spill of undiluted chlorothalonil formulation onto a dry, horizontal metal surface; (2) a spill of undiluted chlorothalonil formulation onto a rapidly rotating shaft; and (3) pouring undiluted chlorothalonil formulation into a container of water. Aerosol generation from these scenarios was compared to that resulting from atomizing dilute chlorothalonil through hydraulic nozzles. Aerosols were captured with a cascade impactor, and quantified by gas chromatography. Results indicated that simulated spill scenarios generated aerosol concentrations between 2.1 and 5.3 ng/l, which were in the same order of magnitude as, and only marginally higher than, the detection threshold (1.7 ng/l) and background levels (2.2 ng/l). In comparison, atomization of dilute chlorothalonil through a hollow cone and flat fan nozzles resulted in airborne concentrations of 354 and 96 ng/l, respectively, related to the atomization characteristics of these nozzles. Measurement of the dimensions of the aerosol cloud indicated that aerosols resulting from a spill amounted to approximately 10(-5)% of the spilled chlorothalonil. It was estimated that a male worker respiring 29 l/min would inhale approximately 0.32-0.78 ng of chlorothalonil during a typical 30 s spill, assuming a 1% transfer efficiency between the spill site and the mixer/loader. These estimates were between 10000 and 480000 times less than literature data for respiratory exposure of chlorothalonil by applicators and harvesters, suggesting that inhalation of aerosols from mixing and loading represents a minor component of overall exposure.

Deposit characteristics and toxicity of fipronil formulations for tobacco budworm (Lepidoptera: Noctuidae) control on cotton

Abstract Three water-dispersible fipronil formulations have been tested for toxicity against second instar tobacco budworm, Heliothis virescens (F.). Topically, EC is the most potent of the three assays followed by WG and SC. However, pick-up assays on parafilm did not show significant differences in toxicity between formulations. Droplet spread and deposit morphology of the formulations were studied on cotton. Although the initial droplet spread was observed to be highest for EC, the final dried deposits of formulations were not significantly different from each other. The deposit patterns of all three formulations on cotton are different. For EC, the formulation/AI is associated with an annulus (outer ring) whereas the WG and SC are particulate in appearance and dispersed across the deposit. From the rain-washing studies on cotton, SEM photographs indicate that SC has greater retention than EC or WG.

Assessment of off‐target movement of orchard pesticides: Capture efficiencies of synthetic and biological biomarkers

Pesticide drift is a symptom of the inefficiency of the hydraulic atomization process and with orchard crops, represents a highly visible process. Assessment of orchard drift, the components of non-target parameters and capture efficiencies of biological biomarkers, are presented in this brief review. Spray deposits downwind from orchard sprays is a reflection of the atomizing system, orchard geometry, seasonal and meteorological condition, as well as the non-target surface characteristics. Downwind ground and airbome drift is captured differently on strings vs. plastic acetate ground collectors, high air volume samples and natural vegetation. Significant differences in pesticide retention can also occur between apple cultivars, for example, and which may be due, in part, to leaf hair density. A wind tunnel device to measure relative capture efficiencies of passive dosimeters demonstrates the potential for significant differences in droplet capture due to surface morphology. Spray drift passing over bare ground, vs. vegetation, deposits differently and the use of windbreaks and buffer zones to mitigate spray drift is being encouraged by policy makers. Data on potential use of biological lethal distance (LD 50 ) values for non-target organisms lends credence for identifying the magnitudes of real-world risks occurring as off-target movement of orchard pesticides.

Spray deposits: Opportunities for improved efficiency of utilizationvia quality, quantity and formulation

Pesticides are under an increasing array of criticism by the public and policy makers as being excessively hazardous to the environment. This has resulted in a wide variety of pesticide use reduction programs for agriculture worldwide. These include less active ingredient per unit area, safer products, and new delivery systems. As a result of these policies, and regulatory thrusts, there are numerous opportunities for improved efficiency of utilization with a better understanding of droplet placement criteria, including spray droplet quality,e.g. size/density parameters, formulation interactions, and a better educated user. This minireview revisits some recent trends in our efforts to improve the dose-transfer efficiency of the modern crop protection agents.

Efficacy of bifenthrin against pyrethroid-resistant and -susceptible populations of glasshouse whitefly in bioassays and using three spray application methods

Abstract Bioassays were performed using uniformly-sized drops to reflect exposure of pyrethroid-resistant and -susceptible populations of Trialeurodes vaporariorum Westwood to ultra-low-volume (ULV) spray deposits of bifenthrin. These assays provided good estimates of the optimum concentration of bifenthrin required to control each population when plots of whitefly-infested poinsettias were treated with ULV charged and uncharged sprays. In some assays the Ohio population was > 100 times more resistant to bifenthrin than the susceptible whitefly strain. Conventional high-volume (HV) spraying was as effective as both charged and uncharged ULV sprays against the resistant population, but none of the methods resulted in acceptable control at the maximum label rate. The charged spray was significantly more effective at controlling the susceptible strain than the other methods, causing 98% mortality at approximately one-half the minimum recommended rate. Although bifenthrin has been used on ornamentals in Ohio for only 2 years, there is already evidence that this pyrethroid is no longer effective against a local whitefly population. The bioassays and spray studies described here demonstrate that this lack of effect is attributable to resistance and not to poor application or ‘field failure’.

Effect of formulation, droplet size, and spatial distribution on dose transfer of pesticides

Spray application is a complex and dynamic process involving many interdependent components. Improvements in pesticide use efficiency will require a more intensive study of the physical and physiochemical parameters controlling droplet dynamics, deposition on defined targets and biological response. The biological effect depends on the toxicological properties of the active ingredient (AI), its formulation, the concentration and pattern of the dose at the point of action. Changes in formulation of a pesticide may result in significant changes in pest response to and hence transfer of a toxin. Encapsulation of insecticides showed significant changes in avoidance/irritant reactions by certain pests vs that recorded for standard formulations. Droplet size also affected the performance of materials tested. Separation of drop (and particle) size, concentration, and formulation effects can be useful in understanding toxin activity and developing accurate parameters for specific targets and crop protection agents.

Evaluation of a No-Touch Pesticide Use System

There are increasing problems (real and perceived) associated with the handling of pesticides in agriculture. All known data reveal that the greatest levels of exposure encountered with the use of a pesticide occurs at the mixer-loader stage. LPCAT and Merck initiated a collaborative, designed laboratory and field study to evaluate the potential of a series of dissolvable bags for use in boom and airblast sprayers. In laboratory studies, the effect of temperature on bag dissolution was a non-linear inverse relationship. Water hardness had no effect on bag dissolution. The field tests included mechanical and by-pass agitation sprayers with numerous concentration spray volumes. The protocols included: variation in tank levels prior to the addition of bags, check points at suction strainers, and in-line filter and nozzle strainer observations at 10 min, 1 h, and 4 h, including 1 h down time. The QSA 2004 bag reduced foaming of the wettable powder formulation. The QSA 2000, 2004, and Monosol 8000 were successful in low volume tank mixes in hydraulic and mechanized agitation sprayers.