W. C. Hoffmann

Spray Characterization of Ultra-Low-Volume Sprayers Typically Used in Vector Control

Abstract Numerous spray machines are used to apply pesticides for the control of human disease vectors, such as mosquitoes and flies, and the selection and setup of these machines significantly affects the level of control achieved during an application. The droplet spectra produced by 9 different ultra-low–volume sprayers with oil- and water-based spray solutions were evaluated along with 2 thermal foggers with the use of diesel-based spray solutions. The droplet spectra from the sprayers were measured with the use of laser diffraction droplet sizing equipment. The volume median diameter from the sprayers ranged from 14.8 to 61.9 µm for the oil-based spray solutions and 15.5 to 87.5 µm for the water-based spray solutions. The 2 thermal foggers generated sprays with a volume median diameter of 3.5 µm. The data presented will allow spray applicators to select the spray solution and sprayer that generate the droplet-size spectra that meet the desired specific spray application scenarios.

Differentiation of Cotton from Other Crops at Different Growth Stages Using Spectral Properties and Discriminant Analysis

The spectral reflectance properties of cotton (Gossypium hirsutum L.), corn (Zea mays L.), soybean [Glycine max (L.)], and sorghum [Sorghum bicolor (L.)] crops during their different growth stages were examined, and spectral data were used to distinguish cotton from other crops. Two field blocks with two different soil types, Belk clay (BaA) and Ships clay (ShA), were set up with cotton, corn, soybean, and sorghum in each block and grown using conventional production practices for the area. Spectral information was collected from all crops at different growth stages from May to July 2009. Reflectance spectra and the first derivative of the spectra were analyzed to characterize the spectral properties of crop types and compare the crops grown in different soil types. The red-edge points of cotton, soybean, and sorghum shifted with the growth stage. Principal component analyses were successful in reducing the dimensionality of the hyperspectral data and identifying significant features from the original data. Most significant wavelengths selected were in the 548-556 nm, 679-682 nm, 756-764 nm, and 928-940 nm regions of the spectrum. Discriminant analysis was able to differentiate cotton from other crop types at four critical growth stages with 100% accuracy of classification for all four observation dates.

Remote Sensing and GIS Applications for Precision Area-Wide Pest Management: Implications for Homeland Security

Area-wide pest management essentially represents coordinated adoption of integrated pest management to conduct preventive suppression of a pest species throughout its geographic distribution. Scientists and researchers in area-wide pest management programs have been developing, integrating, and evaluating multiple strategies and technologies into a systems approach for management of field and crop insect pests. Remote sensing, Global Positioning Systems, geographic information systems, and variable rate technology are additional tools that scientists can implement to help farmers maximize the economic and environmental benefits of area-wide pest management through precision agriculture.

Volumetric Collection Efficiency and Droplet Sizing Accuracy of Rotary Impactors

Measurements of spray volume and droplet size are critical to evaluating the movement and transport of applied sprays associated with both crop production and protection practices and vector control applications for public health. Any sampling device used for this purpose will have an efficiency of collection that is a function of the sampling device itself, the droplet size of the spray being sampled, and the airspeeds under which the sampling is conducted. This study focuses on two rotary impaction devices, the Hock and the FLB samplers, that were evaluated under two droplet sized sprays and four airspeeds. The collected spray concentrations were compared to standard passive samplers whose theoretical collection efficiency was calculated and used to estimate the actual spray volume sampled. Additionally, droplet sizing information derived from image analysis of droplet deposits on the rotary impactor collection surfaces was compared to actual measurements of droplet size of the sampled spray cloud. Generally, overall collection efficiencies ranged from 2.5% to 20%, with the FLB being more efficient than the Hock and with lower efficiencies at higher airspeeds for both samplers. Comparison of the droplet sizing data showed that the FLB sampler tended to underpredict the DV10 and DV50 data, while the Hock tended to overpredict the DV50 and DV90 data.

Further evaluation of spray characterization of sprayers typically used in vector control.

Abstract This work reports droplet-size data measured as part of a collaborative testing program between the US Department of Agriculture, Agricultural Research Service, and the US Navy, Navy Entomological Center for Excellence. This is an ongoing relationship that seeks to test new and revised spray technologies that may potentially be used by deployed personnel. As new equipment comes to market or when existing equipment is modified they are all integrated into this annual testing. During the 2011 equipment evaluations, 24 sprayers were operated across their range of available settings (pressure and flow rate), using both water and oil solutions. Droplet-size data as measured with laser diffraction ranged from 4 to 223 µm (volume median diameter). Generally, as the spray rate increased, droplet size increased, and as the pressure increased at a given same spray rate, droplet size decreased. This information allows users to set up and operate these sprayers in a manner such that a particular droplet size is applied optimizing efficiency and efficacy of applications.

Correction of Spray Concentration and Bioassay Cage Penetration Data

Abstract Field trials were conducted to demonstrate the need for correcting sampled spray concentration data for sampler collection efficiencies and estimated spray exposure levels in mosquito bioassays for cage interference effects. A large spray block was targeted with aerial spray treatments of etofenprox in order to create a gradient in both spray concentration and mortality. Spray concentrations were measured using rotary impactors, which were coupled with caged bioassays. Measured spray concentrations were corrected for sampler collection efficiencies, which ranged from 55% to 15%. The corrected spray concentrations were then used to estimate the spray levels inside the bioassay cages. Given the cage type used (Townzen type) and wind speeds occurring during the spray trials (2–4 m/sec), concentrations inside of the bioassay cage ranged from 65% to 68% of that measured within the spray block. Not correcting for the combination of sampler collection efficiency and cage interference, underestimated spray concentration levels inside the cages were 76–90%. Correcting field-measured data allows not only better comparisons between differing studies, but can also provide better estimates of caged insect mortality versus actual spray concentration exposure levels.