Influence of formulations and time of day on Dicamba air concentrations following treatment

Authors: FARRELL, S - University Of Missouri; Lerch, Robert; BISH, M - University Of Missouri; BRADLEY, K - University Of Missouri

Submitted to: Weed Science Society of America Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 10/31/2017
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Few studies have been conducted to understand the extent to which newly-labeled dicamba formulations are present in the air following application. The objectives of this research are to determine the effects of time of application, surface temperature inversions and new formulations on the concentration of dicamba detected in the air following application. A series of field experiments were conducted near Columbia, Missouri during the summer of 2017. Air samplers were placed equidistantly within 6 x 31 m plots and 31 cm above the canopy prior to dicamba applications to obtain background levels of dicamba. Air samplers were removed immediately prior to dicamba application, and then returned to the treated field 30 minutes following application. Applications were made at the 1X rate for each product, and plots were a minimum of 480 m apart. Glass fiber filters and polyurethane foam substrates (PUF plugs) from the air sampling machines were replaced at set intervals throughout the experiments, which extended up to 72 or 96 hours following application. A methanol wash was used to extract dicamba from the filter paper and PUF plugs, and HPLC-UV was utilized to detect dicamba. Preliminary results from two experiments in which Xtendimax plus VaporGrip and Engenia were applied at the same time showed the majority of dicamba, regardless of formulation, was detected in the first 0.5 to 8 hours after treatment (HAT). The average concentration of dicamba for the Xtendimax treatment was 26.5 to 31.1 ng/m3 while that for Engenia was 18.4 to 20.5 ng/m3. By 24 to 48 HAT, dicamba levels had declined to less than 3 ng/m3 for each treatment. In a separate experiment, simultaneous afternoon applications resulted in dicamba concentrations of at least 20 ng/m3 and 12 ng/m3 for Engenia and Xtendimax plus VaporGrip, respectively. The majority of dicamba from the Engenia treatment was detected 16 to 24 HAT while the majority of Xtendimax plus VaporGrip was detected 8 to 16 HAT. Results from two experiments in which both formulations were applied without inversion conditions and with the addition of glyphosate revealed the majority of dicamba was detected 0.5 to 8 HAT, regardless of formulation, at concentrations of 20.5 ng/m3 and 21.6 for Engenia and Xtendimax plus VaporGrip, respectively. Across four experiments in which Xtendimax plus VaporGrip was applied during inversion conditions with glyphosate, average dicamba concentrations from 0.5 to 8 HAT reached the highest observed in any study at 34.2 ng/m3. For those studies in which Xtendimax plus VaporGrip was applied alone or with the addition of glyphosate (n=83), correlation analyses showed that dicamba concentrations in air were significantly related to maximum night time air temperature (r = -0.720; p <0.001) and wind speed (r = -0.723; p <0.001). This indicated the importance of atmospheric stability to the aerial transport of dicamba. In addition, dicamba was detected at 9.25 ng/m3 in the afternoon following application, suggesting that volatilization was also a contributing factor to transport. These preliminary results indicated that dicamba was routinely detected in air following application regardless of formulation, and its concentration in air was strongly affected by atmospheric stability.