Roger A. Downer

Deposit structure and efficacy of pesticide application. 1: Interactions between deposit size, toxicant concentration and deposit number

Application of pesticides through a hydraulic nozzle produces deposits on a plant surface which have a spatial structure with elements of deposit size, number per area, and toxin per deposit. To investigate the relative contributions of these elements to the interaction of deposit structure and toxicant efficacy, we used a stochastic cellular automaton model of diamondback moth feeding on Bacillus thuringiensis (Bt)-treated cabbage – the Pesticide Dose Simulator (PDS) model. Data were analyzed using a specialized response surface approach called a mixture design. The advantage of this design was that it integrated the effects of deposit size, number per area and toxin per deposit on toxicant efficacy. Results from PDS simulations led to the following conclusions: (1) Deposit structure plays a major role in toxin efficacy. (2) Small deposits are not always the most efficacious. (3) Uniform coverage is not the best deposit structure if one is forced to limit application rates and field persistence. (4) Since uniform deposit structures allow an insect to live longer, uniform deposit structures should result in more insects acquiring sub-lethal doses. This may result in an interaction between ‘uniform coverage’ and the development of pesticide resistance in insect populations. (5) Percentage mortality and the level of crop protection are not necessarily correlated. Overall, these results help reconcile laboratory observations that small droplets are more efficacious with field observations that application of small droplets (eg from spinning disk sprayers) does not necessarily increase field efficacy. © 1999 Society of Chemical Industry

Oral toxicity of essential oils and organic acids fed to honey bees (Apis mellifera)

Summary Natural plant products have been studied for potential use as in-hive fumigants for suppression of parasitic mites and other pests. A more direct application through direct feeding of bees would avoid problems with fumigant volatility in cold climates and provide a more systemic route of exposure for the target pest. However, there must be a balance between toxicity to hive pests and toxicity (safety) to the bees. We focused on adult bee toxicity when testing ten products: cineole, clove oil, formic acid, marjoram oil, menthol, oregano oil, oxalic acid, sage oil, thymol, and wintergreen. Each product was tested at several concentrations in a sugar syrup fed to bees over several days, and dead bees were counted daily. Oxalic acid was the most toxic of the products tested. Menthol and cineole had mortality levels no different from controls fed plain syrup after 8 days of treatment. At 14 days of treatment, wintergreen was the least toxic, but neither menthol nor cineole were a part of the testing that went to 14 days. Our results indicate that the tested products could all be used safely for treating bees orally if dose is carefully managed in the hive.

Effects of spray adjuvants on swath patterns and droplet spectra for a flat-fan hydraulic nozzle

Abstract The effects of seven agricultural adjuvants and two polymeric drift retardants on the distribution of spray were compared with water applied through a multiple nozzle boom. Similarly, the effects on droplet spectra from a single XR80004VS nozzle operating at 276 kPa (40 p.s.i.) were compared. Except for two adjuvants, swath pattern relative to water was significantly altered. With one exception, droplet spectra parameters relative to water were shifted to both smaller and larger frequency distributions. The polymers, whether sprayed alone or in mixture, had the greatest effect on swath pattern. The polymers sprayed alone had the greatest effect on droplet spectra, but the mixtures gave a more variable response. Swath patterns and droplet spectra derived using water are not, therefore, representative when spraying pesticides with adjuvants. Dynamic surface tension (DST) and viscosity at high shear rates were measured for all spray solutions. Analysis to determine the feasibility of predicting quality of swath pattern and various spray spectra parameters (e.g. VMD, NMD) showed that the interaction between the two physicochemical parameters and the results of atomization are complex. DST and viscosity were poor predictors when applied to the mixtures of polymers and conventional adjuvants tested.

Theory and practice of microbial insecticide application

Spray application takes input from a wide range of disciplines, from the traditional crop protection disciplines of entomology,weedscience, and plant pathology, formulation chemistry, and agricultural engineering, to those of fluid dynamics, meteorology, and others. In general, spray application is either largely ignored–one just sprays a crop with a microbial control agent (MCA)–or it is seen as a panacea for all ills, increasing the efficacy and effectiveness of an MCA to the point of commercial viability. Spray application is neither.

Deposit structure and efficacy of pesticide application. 2 : Trichoplusia ni control on cabbage with fipronil

Pesticide deposits have a spatial structure having elements of size, number per area and toxicant per deposit. To investigate the relative contributions of these elements to the efficacy of the deposit structure, we developed a bioassay using the cabbage looper (Trichoplusia ni), cabbage, and a soluble concentrate formulation of fipronil [(±)-5-amino-1-(2,6-dichloro-α,α,α-trifluoro-p-tolyl)-4-trifluoromethylsulfinylpyrazole-3-carbonitrile]. The bioassay manipulated deposit structure by changing the number, toxicant concentration of the solution, and size of droplets used in creating deposits. The bioassay methodology was developed as an extension from standard industrial mixture experimental designs. Results from the bioassay led to the following conclusions: (1) Deposit structure plays a major role in toxicant efficacy. (2) The effect of droplet size is roughly equal to the effect of concentration, while both these factors may have a greater effect than droplet number. (3) The interactions between the factors of deposit size, deposit number, and concentration are more important than any single component. (4) Uniform coverage is not the most efficacious deposit structure if one is forced to limit application rates, and field persistence. (5) Uniform deposit structures have less variability in their biological effect than do more heterogeneous structures-though the relationship is not linear. These bioassay data corroborate the predictions of an earlier paper.

Use of nozzle-induced air-entrainment to reduce active ingredient requirements for pest control

Abstract A simple nozzle design/modification is presented which takes advantage of the known effect of the increasing biological efficacy of a pesticide with decreasing drop size for insecticides and perhaps fungicides. However, applying active ingredient (AI) in unassisted fine sprays leads to poor canopy penetration and increased drift hazard. Therefore, the air entrained by medium-coarse nozzles spraying water is utilised to impart kinetic energy to a finer spray containing AI. A fine nozzle is sprayed into a medium-coarse spray at an angle of approximately 15 ° from vertical approximately 10 cm below the medium-coarse nozzle, spraying into the direction of travel of the sprayer. The subsequent spray cloud consists of: small drops, typically The atomisation characteristics and potential drift problems of such a nozzle system were investigated. The results show that the velocity characteristics of the carrier (medium) spray were imparted to the fine spray, removing the problem of low spray cloud kinetic energy. Coalescence of drops in-flight was approximately 50%. Drift measurements in a large wind tunnel showed that drift increased four-fold at 4 m/s windspeed and approximately two-fold at 2 m/s. Taking into account the expected reduction in AI requirements, at 2 m/s, drift was quantitatively approximately the same as that of the medium nozzle.

The application of biological pesticides: Limitations and a practical solution

Biopesticides and agrichemicals are applied using basically the same equipment. The limitations imposed on biological or conventional chemical pesticides by current application systems are discussed. In general, any pesticide must be applied into a crop using the commonly used application system in that crop. This will normally be the hydraulic nozzle. Researchers attempting to increase the efficacy of a biopesticide by changing application system should bear in mind the constraints set by farmers on altering their usual spraying practices. These constraints are considered along with the criteria required for the successful market introduction of a novel application system. A novel application system, the “double nozzle” is introduced, which fulfils the criteria discussed, in particular the reduction in terms of amount of active ingredient required for pest control. The scientific rationale for this new system is explained, and its performance discussed.RésuméEn principe, biopesticides et produits agrochimiques sont pulvérisés à l’aide du même équipement. Les limitations imposées aux pesticides biologiques aussi bien qu’aux produits chimiques conventionnels par les systèmes d’application couramment utilisés sont discutées. Quels que soient les pesticides utilisés, ils seront généralement appliqués sur une certaine culture à l’aide du même matériel d’épandage, le plus communément employé pour ce type de culture, c’est-à-dire normalement des buses hydrauliques. Les chercheurs qui tentent d’augmenter l’efficacité d’un biopesticide en modifiant le système de pulvérisation devraient garder à l’esprit les réticences des cultivateurs à l’égard de tout changement dans leurs pratiques d’épandage. Ces contraintes sont examinées en détail, ainsi que les critères requis pour commercialiser avec succès tout nouveau système d’application. Un système nouveau de pulvérisation appelé la ’double buse’ est présenté, lequel satisfait aux critères discutés ci-dessus, en particulier en termes de réduction des quantités d’ingrédients actifs utilisés pour lutter contre les nuisibles. Les arguments scientifiques qui plaident en faveur de ce nouveau système sont expliqués et ses performances discutées

Dose transfer of Bacillus thuringiensis from cabbage to the diamondback moth: A graphical simulator

Abstract The application of agrichemicals is a highly inefficient process and one of the main causes of the environmental and health risks currently associated with pesticide usage. Efforts to mitigate this inefficiency have largely been unsuccessful, due principally to the poor understanding of the processes involved in the spray application of pesticides, from atomization to biological effect. A generalized model of the application system for pesticides from atomization to biological result is described in this overview. The model allows the investigation of the biological consequences of altering the application parameters for the bacterial insecticide Bacillus thuringiensis when used against the diamondback moth (Plutella xylostella L.) with cabbage as the substrate. Parameters input into the model include the in‐flight droplet size frequency distribution of the spray cloud, spatial distribution of the deposit, spread and subsequent environmental degradation of the deposit, and behavioral and toxicolo...

SUMMARY OF STUDIES OF COREXIT DISPERSANT DROPLET IMPACT BEHAVIOR INTO OIL SLICKS AND DISPERSANT DROPLET EVAPORATION1,2

ABSTRACT This paper presents the results of two related studies concerning the aerial application of dispersants. The first study characterized the interactions of various sized Corexit 9500 and 95...

Calibrating the pesticide capture efficiency of passive dosimeters

A system has been devised for determining the absolute capture efficiency of passive dosimeters. The system is composed of three components : a wind tunnel, a tracer atomizer, and a capture efficiency test device (CETD). The CETD consists of a series of cylinders separated by nylon screens to intercept and capture the spray containing a tracer. The decline in tracer at the screens was used to determine the tracer incident on the first screen. This in turn was used to estimate the tracer incident on a test dosimeter of washed muslin. The capture efficiency of the dosimeter was expressed as the ratio of tracer captured to tracer incident on the dosimeter. The capture efficiency of the test dosimeter using the CETD was found to be independent of the time of exposure and quantity of tracer captured. The approach presented is novel in that the method for documenting capture efficiency does not require prior knowledge of the spray concentration. Elimination of this requirement allows the use of the device in a much larger array of test situations (e.g. field and greenhouse studies) than has been previously possible. Furthermore, the conceptual model can easily be modified to allow for capture efficiency measurements from a range of structures and materials such as plants or whole leaves, as well as insects and non-target animal species. The CETD is simple and portable and could be used to calibrate dosimeters in a variety of field situations.