Auxin Herbicide Drift vs. Volatility

A headline that reads “New dicamba formulations do not reduce drift: Part III” preceded an article that was posted by Forrest Laws for the Delta Farm Press on Mar. 2, 2017. Naturally, this headline caught my attention.

In the first paragraph of the article following the headline, the author references comments made by farmers that new formulations of dicamba for use on dicamba-tolerant crops will reduce drift. In the second paragraph, the author references comments made by Dr. Kevin Bradley, Extension Weed Scientist at the Univ. of Missouri, who states that the new formulations do not reduce the potential of auxin herbicides to drift when they are applied improperly.

A complete and thorough review of the potential issues surrounding the use of auxin herbicides 2,4-D and dicamba on tolerant crops is presented in a 2012 article published by Purdue University Extension. Especially pay attention to the section “Factors Affecting Off-Site Movement”, which includes segments on drift, which is the physical movement of spray particles by wind away from the target, and volatility, which is the movement of the gaseous form of the herbicide after its deposition on the intended target. These are the two contributing components to off-site movement of these herbicides.

Off-target damage caused by the auxin herbicides results when either the liquid or gaseous form of the herbicide moves away from the intended target area. The following narrative describes drift processes and mitigating factors.

Drift is the physical movement of herbicide sprays away from the targeted object or area after leaving the sprayer at the site of application. Drift usually occurs in windy conditions and/or when improper spraying techniques are used. The goal with herbicide applications is to have spray particles that are small enough to result in adequate coverage with the herbicide being applied, but large enough to reduce its drift potential.

Herbicide drift can occur with any herbicide, but the risk of damage to non-target areas varies among herbicides and among non-target plants that are located in the drift path. With auxin herbicides, the potential damage from drift is especially significant because of the high sensitivity of many plant species that will be growing outside the target area. As Dr. Bradley stated above, the new formulations of the auxin herbicides do not reduce their drift potential when they are improperly applied.

Factors that affect the propensity for drift are nozzle type and spray angle, sprayer boom height, wind speed and direction, spray pressure, and temperature inversion. The criteria for the safe application of auxin herbicides to reduce or prevent off-target drift are contained in each herbicide’s label, and must be followed precisely when applying these herbicides. Click here for a detailed discussion of this information.

That leaves volatility of the auxin herbicides to address. As stated above, volatility is the movement of the gaseous form of the herbicide after its application on the intended target. This is where the new formulations of the auxin herbicides come into play; they are designed to reduce volatility.

So here is the take-home message. Reduction in drift of auxin herbicides away from the target is controlled by or relies on the array of strict application directions specified on each product’s label, whereas the new formulations of these herbicides are intended to reduce volatility.

Click here for a post on this website that contains additional information about auxin herbicides and their application to auxin-resistant crops.

Composed by Larry G. Heatherly, Mar. 2017, larryheatherly@bellsouth.net