Determination of Cotton Plant Injury by Aerial Application of Glyphosate Using Remote Sensing and Spray Drift Sampling

Off-target drift of aerially applied glyphosate can cause plant injury, which is of great concern to farmers and aerial applicators. To determine the extent of crop injury, an experiment was conducted from a single aerial application of glyphosate to evaluate the effects of near-field drift.  For identification of the drift effect on different crops, a field was planted in alternating blocks of cotton, soybeans, and corn. Spray samplers were placed in the spray swath and in several downwind orientations to quantify relative concentration of applied spray. An Air Tractor 402B spray airplane equipped with fifty-four CP-09 nozzles flew down the center of the field to apply 22 oz/acre of Roundup Weathermax and Rubidium Chloride tracer at a 5 gal/acre spray rate.  Hyperspectral data obtained from spectroradiometer readings were acquired from selected cotton plants at one week intervals, and aerial Color-Infrared (CIR) imagery was obtained using a Global Positioning System (GPS)-triggered Geospatial Systems MS-4100 camera system. This study’s main focus is to assess glyphosate spray drift injury to cotton using the CIR imagery. Spectroradiometer data will be analyzed to determine spectral differences between injured and non-injured plants. These data will be further compared with data from spray drift samplers placed downwind. Results will be helpful for determining the extent to which near-field drift sampling can be a viable tool for determining the extent of damage relative to derived concentrations of glyphosate.