Submitted to: Journal of ASTM International
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/28/2009
Publication Date: 1/10/2010
Citation: Fritz, B.K., Hoffmann, W.C., Parker, C.T., Lopez, J. 2009. Development and testing of a laboratory spray table methodology to bioassay aerial spray drift. Journal of ASTM International. 6(6):Paper ID JAI102125. Interpretive Summary: Biological damage resulting from spray drift is a major concern for aerial applicators, but information relating biological damage to specific spray deposition levels downwind of an application is limited. Obtaining this type of data from full-scale field studies is cost prohibitive, therefore a laboratory method for assessing biological damage from spray drift was devised. A laboratory spray table, which allowed control over the amount and droplet size characteristics of deposited spray materials, was used to apply a herbicide to greenhouse grown plants at low concentrations equivalent to levels detected by previous field measurements. Indicators of plant health were recorded and biological response models relating plant health and deposition levels were developed. Data collected from ongoing studies of this type will be tested in full scale aerial drift studies and ultimately included in application decision support systems that provide applicators an additional tool when making application decisions.
Technical Abstract: The objective of this work was to develop a repeatable methodology for bioassaying simulated levels of aerially applied glyphosate at deposition levels ranging from 1/3 to 1/100 of labeled rate at droplet sizes of 100 µm in a spray table environment. These drift deposition levels are consistent with downwind drift measurements out to 200m seen in previous field studies focusing on quantitative drift assessment. Additionally, full rate applications were included for comparative purposes. The deposition levels were obtained by varying nozzle traverse speed and plant location under the nozzle. Ten replications were conducted at each targeted rate applying glyphosate to container grown-plant samples. Deposition was measured on mylar cards through fluorometric analysis. Plant health measures (height and Normalized Difference Vegetation Index (NDVI)) were taken at 0, 1, 3, 5, 7, and 14 days after treatment. An equal number of non-treated control plants were analyzed alongside treated plants. Deposition and plant health data were used to generate dose-response relationships. Dose-response curves relating change in plant height and change in measured NDVI values corresponding to deposition levels were generated. This methodology is one that can be implemented across a wide variety of plant and pesticide combinations. Collected data from this, and future studies will be tested under field conditions and ultimately be included in application decision support systems that integrate spray drift modeling results with established dose-response relationships.