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ARS Home » Southeast Area » Stoneville, Mississippi » Crop Production Systems Research » Research » Publications at this Location » Publication #263448
Title: Assessing crop injury caused by aerially applied glyphosate drift using spray sampling

Author
item Huang, Yanbo
item DING, WEI - Northeast Agricultural University
item Thomson, Steven
item Reddy, Krishna
item Zablotowicz, Robert

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/2012
Publication Date: 7/1/2012
Citation: Huang, Y., Ding, W., Thomson, S.J., Reddy, K.N., Zablotowicz, R.M. 2012. Assessing crop injury caused by aerially applied glyphosate drift using spray sampling. Transactions of the ASABE. 55(3): 725-731.

Interpretive Summary: Crop injury caused by off-target drift of aerially applied glyphosate is of great concern to farmers and aerial applicators. An experiment was conducted to determine the extent of the injury due to near-field glyphosate drift from aerial application to glyphosate-sensitive cotton, corn and soybean. The drift effects on different crops were characterized in a field planted in alternating blocks of these sensitive crops. Spray samplers were placed in the spray swath and downwind to quantify relative concentration of applied chemical. An agricultural airplane was flown down the center of the field applying Roundup Weathermax herbicide. The spray deposition was estimated based on the measurement of the spray samplers. Plant height and chlorophyll response to gyphosate drift was assessed at weekly intervals. Statistical analysis indicated that spray drift sampling was able to explain downwind crop injury, and physical responses could be estimated for evaluating crop damage caused by the drift of aerially applied glyphosate. Correlations between the glyphosate spray deposition and the crop biological responses indicated that impact of the glyphosate drift on cotton was less sensitive than corn and soybean.

Technical Abstract: Crop injury caused by off-target drift of aerially applied glyphosate is of great concern to farmers and aerial applicators. An experiment was conducted in 2009 to determine the extent of injury due to near-field glyphosate drift from aerial application to glyphosate-sensitive cotton, corn and soybeans. The drift effects on different crops were characterized in a field planted in alternating blocks of these sensitive crops. Spray samplers were placed in the spray swath and downwind to quantify relative concentration of applied chemical. An Air Tractor 402B spray airplane equipped with fifty-four CP-09 nozzles was flown down the center of the field applying 866 g ai/ha Roundup Weathermax and Rubidium Chloride tracer at a 2.6 g/ha spray rate. Relative concentrations of this tracer were quantified from downwind spray samplers by atomic absorption spectroscopy. Biological responses of the crops to the glyphosate drift were measured at weekly intervals, along with airborne multispectral imaging. Statistical analysis indicated that spray drift sampling was able to explain downwind crop injury, and physical responses could be estimated for evaluating crop damage caused by the drift of aerially applied glyphosate. Correlations between the glyphosate spray deposition and the crop biological responses identified that impact of the glyphosate drift on cotton was less sensitive than corn and soybean. Regression models for cotton and soybean one and two weeks after field treatment and for corn one week after treatment were developed and evaluated respectively with chlorophyll data. The cotton models at one and two week after treatment with visual injury and plant height were well validated with chlorophyll data (average 1 ratio of the estimated and measured chlorophyll and the low root mean squared deviations). However, in validation of the corn model the ratio of estimated vs. measured chlorophyll deviated from 1. Compared with validation of the corn model, the validation of soybean models showed less bias with a close to 1 ratio of the estimated and measured chlorophyll. These results have established a method of characterizing crop injury caused by aerially applied glyphosate and can provide guideline data for use by farmers and aerial applicators.