Experiment 1: Two locations (EV Smith research and extension center, and TN Valley research and extension center) will be used for this experiment to evaluate how dicamba vapor damages sensitive soybeans as compared to simulated particle drift in the summer of 2019. A sensitive soybean variety will be planted in early-mid May and treated in R1 stage. Experimental design will be RCBD with 4 reps. Plot size will be 25 ft long by 12 ft wide (4 rows of soybean). Each low tunnel (25 x 6 x 3 ft) will be used to seal dicamba vapor following application on two soil pans (10 x 7.5 x 2.5 in). 1/1000x, 1/100x, 1/10x, 1x, 10x and 20x label rates of dicamba (Xtendimax) will be used to spray soil pans. Then, soil pans will be carefully placed in the middle of each plot without touching the foliage of soybean, and low tunnels will be installed immediately afterwards with all edges sealed with soil. Following the installation of low tunnels, other plots not covered by low tunnels will be sprayed with 8 different rates (1/16000th – 1/4th of full label rate) of Xtendimax over the top of sensitive soybean. Injury ratings will be conducted 7, 14 and 28 days after application. Foliage samples will be taken from 5 rates of selected particle drift plots for dicamba quantification analysis through a commercial lab. Soybean yield will be taken in each plot at the end of season. Data will be analyzed in SAS 9.4 in a mixed model with a=0.05 level.

Experiment 2: A location in NW or North AL will be identified to conduct this study in summer of 2019. This field will be at least 70 acres, relatively uniform in size and represents the typical geographic conditions of soybean fields in this area. A dicamba resistant variety will be planted in this field (4-8 rows of a sensitive variety may be planted along field edges to surround the resistant variety to show efficacy of dicamba particle drift reduction when label requirements are followed). The same sensitive soybean variety will be planted in 4 inch pots to establish seedlings at Auburn University, then these seedlings will be used for field bioassays to detect dicamba vapor. Two 10 acre rectangle or square blocks will be marked in the middle of this field with a minimal distance of 500 ft between each other. Then, at 30 days after planting (late June or early July), 1) Engenia + Roundup Powermax + Intact, 2) Xtendimax + Roundup Powermax + Intact will be sprayed to each box with Teejet TTI 11004 at 15 GPA and 60 PSI. Boom height will be kept at 24 inch above canopy. Application will be made in late morning when there is no temperature inversion. Wind speed will be in the range of 3-10 MPH. A weather station will be positioned in the middle of the field to document wind speed, direction, temperature, air humidity and other weather data. After spraying has concluded, the soybean bioassays pots will be put around two treated blocks in transects similar to the design in 2018 field study. Bioassays will be collected after staying in the field for 48 hours and kept in greenhouse for measuring height, visual injury and biomass after 1 month of growth. Bioassays will be watered 3 times a day while in the field. Dicamba vapor samples may be collected in this experiment with battery powered air samplers and PUF if labor and funding allow.