Jul 8, 2020
Measuring Herbicide Volatility
The volatility of herbicides, or the change from a solid or liquid to a gas, is dependent on several environmental factors and is extremely variable. We have been working on finding a replacement for Glyphosate for non-crop weed control and have tried to determine the stability of the potential herbicide alternatives. There are various methods used to measure herbicide volatility. All herbicides are initially tested in the laboratory to determine volatility and other properties. Volatility is specifically measured by placing a given volume of herbicide in a container, exposing it to various temperatures and humidity’s and then weighing how much is left. This is done under very controlled conditions. Another technique that is often the next step is to conduct bioassay studies in a greenhouse. This usually involves placing a container with the herbicide spray solution in a closed environment with sensitive plants. Injury to the bioassay plants are measured visually or by some other means. Field Studies are often conducted to measure herbicide volatility. This technique is the most applied, but the results are often imprecise and variable depending on environmental conditions. This commonly involves spraying an isolated area in the field and after the spray has settled placing sensitive plants at variable distances and directions away. Injury is observed or measured at variable time periods. We used this technique on June 10 to June 15 this year at the Yuma Valley Agriculture Center to measure volatility of 13 herbicides we are evaluating as alternatives to Glyphosate. Seven X 10 Ft. plots were sprayed, and tomato plants were placed 25Ft. away from each sprayed area on the north, south, east and west corners 1 hours after application A 50 Ft. buffer separated each sprayed plot. Visual injury was measured to the tomato plants at 24 and 48 hours after they were placed in the field. The 13 herbicides were used in this trial included 5 modes of action and are listed below.
![200708-03 200708-03](/images/default-source/agricultural-ipm/veg-ipm-update-images/200708-03.png?sfvrsn=584f5a36_2&MaxWidth=700&MaxHeight=&ScaleUp=true&Quality=High&Method=ResizeFitToAreaArguments&Signature=1458193D36EAD01E7C971C80323A0ACA93D502C6)
The temperature reached above 100 F, the humidity was 10 to 20% and wind was 5 to 10 MPH during the trial. No injury symptoms were observed to any of the tomato plants from any of the herbicide treatments. The trial included low volatility formulations of the plant growth regulators, 2-4-D (Embed) and Dicamba (Enginia) which are often volatile under these hot and dry conditions. Neither of these two, or any of the other included herbicides, moved 25 ft or more in this one trial. We know, however, that in other trials the results have sometimes been different. Volatility is variable and difficult to measure in field trials.
![200708-04 200708-04](/images/default-source/agricultural-ipm/veg-ipm-update-images/200708-04.png?sfvrsn=27b915c8_2&MaxWidth=700&MaxHeight=&ScaleUp=true&Quality=High&Method=ResizeFitToAreaArguments&Signature=C6A95482F2FD2C3EB305C2CD406595E5A35609F5)
To contact Marco Pena go to:
marcop@ag.arizona.edu