Herbicide formulations can dramatically influence herbicide performance, from efficacy to compatibility to shelf life. Many of the properties are determined by adjuvants, stabilizers, or other additives in the formulation. However, the active ingredient can take multiple forms for some postemergence translocated herbicides. This is because chemists can ‘swap out’ certain chemical building blocks on these molecules. Examples of herbicides that have multiple forms include glyphosate, 2,4-D, and dicamba. This article will focus on the relative volatility of three forms of 2,4-D.
Three common forms of 2,4-D are available on the market: amine, ester, and choline. Many examples of amine and ester formulations exist, but the only products for agricultural uses that contain the choline salt are Enlist One, Enlist Duo, Freelexx, and GrazonPD3. Products for other uses that contain the choline salt are Embed and Embed Extra (orchards) and GameOn (turfgrass).
Applicators wishing to reduce injury to nearby sensitive plants should consider using a product that contains 2,4-D choline. In 2010 and 2011, scientists from the University of Georgia1 sprayed 2,4-D LV4 (ester), Weedar 64 (amine), and an experimental formulation of 2,4-D choline and used injury to sensitive cotton plants as an indicator. These plants were in the field before the herbicide was sprayed and then taken to a greenhouse 2 days later. The ester formulation was associated with injured cotton plants up to 150 feet away, the amine formulation 10 feet away, and the choline formulation was associated with injury 5 feet away. They also placed sensitive cotton plants under a plastic tunnel after the field application and then took the plants to the greenhouse after 2 days. Plants exposed to the ester formulation had 76% injury, amine 14% injury, and the choline formulation had 5% injury.
Regarding herbicide efficacy, some greenhouse research2 suggests that 2,4-D amine and 2,4-D choline controlled glyphosate-resistant marestail (horseweed) similarly; however, 2,4-D choline was more effective on glyphosate-sensitive biotypes. Unfortunately, similar data are unavailable in the literature for other weeds, but it is generally accepted that weed control by 2,4-D amine and 2,4-D choline would be similar in most situations.
Regardless of herbicide formulation, using nozzles and pressures that produce relatively larger droplets will reduce herbicide drift. Drift reduction adjuvants can also reduce drift.
References:
1Sosnoskie et al. 2015
2Ford et al. 2014
Sarah Lancaster, Extension Weed Science Specialist
slancaster@ksu.edu