Submitted to: Scanning
Publication Type: Proceedings
Publication Acceptance Date: February 10, 1998
Publication Date: N/A
Interpretive Summary: Public dismay over excessive use of pesticides, environmental pollution and human health issues provides an impetus for improving conventional spraying systems. Scientists at the USDA, Agricultural Research Service, Application Technology Research Unit (ATRU) are investigating methods of improved pesticide coverage as compared with available, conventional technology. Previous coverage assessment techniques using light microscopes have been limited by the power of visible light to resolve particles down to 0.001mm in size. Light microscopy also lacks the ability to identify chemical elements present. ATRU scientists are using electron beam analysis (EBA) to directly identify the shape and chemical constituents of spray residue crystals. EBA uses a scanning electron microscope with resolving power sufficient to observe particles down to 0.00007mm in size. EBA identifies and measures chemical elements present using a process called energy dispersive x-ray microanalysis. The latter yields data on pesticide crystal shape, size and chemistry that are usually unique to each pesticide and formulation. Computerized photography with EBA produces a digital image that is used to determine effectiveness of spray systems or other phases of the application process. Other methods are used to correlate and confirm EBA residue data, whether conventional or biological control agents.
Technical Abstract: Thorough knowledge of the delivery, dispersal, and fate of fungicides is crucial to insure effective disease management. Agoal of the USDA, Agricultural Research Service, Application Technology Research Unit is to obtain more precise knowledge of pesticide coverage and plant canopy penetration. Accurate fungicide distribution with minimal off-target contamination, enhanced retention of active ingredients onto targeted surfaces, and drift reduction leads to more effective crop management. Conventional coverage assessment methods utilize fluorescent dyes, screens, string and polyethylene tape. Research on more precise application systems, improved pesticide formulations, precise detection and mediation of water status to accommodate optimal pesticide retention are needed. One novel assessment method used is electron beam analysis (EBA). Residues are characterized by their morphology and elemental composition. Digital beam control permits relatively rapid image acquisition, minimizing electron beam damage to hydrated samples. Laboratory research and field studies at production nurseries and greenhouses involve assessment of canopy penetration, pesticide spray distribution, spray drift and associated water relations of target crops. Conductivity measurements of chemical tracers and spectrophotometry of food dyes have been used with EBA in correlative studies. Biopesticide coverage, nontraditional control methods and interactions between pathogens and plant surface structure are being studied to help achieve new and innovative disease management techniques.