Quantifying glyphosate plus 2,4-D or dicamba removal from the surface of totally impermeable film using analytical and bioassay techniques

Abstract

The loss of methyl bromide led to vegetable growers relying more heavily on herbicides to control weeds. Although herbicides can be effective, limited options in vegetable production challenge growers. Identifying new, effective tools to be applied over plastic mulch prior to planting for improved weed control with minimal crop injury would be beneficial. The objective of these experiments was to evaluate the persistence of preplant applications of glyphosate (1,125 or 2,250 g ae ha-1) plus 2,4-D (1,065 or 2,130 g ae ha-1) or dicamba (560 g ae ha-1) over plastic mulch using analytical techniques and subsequent squash and watermelon response. Glyphosate and 2,4-D were not analytically detected at damaging concentrations on plastic mulch when at least 3.5 cm of rainfall was received after application and before planting. Additionally, bioassay results for squash and watermelon supported analytical results with less than 10% visual injury for either crop, with no growth or yield suppression observed. In contrast, dicamba concentrations on plastic mulch, regardless of rainfall amount or time between application and planting, remained at damaging levels. Squash yields were reduced by dicamba applied 1 to 30 days before planting while watermelon was more resilient. 2,4-D plus glyphosate applied preplant over plastic mulch can provide an additional herbicide option for vegetable growers. Additional research is needed to understand the impact of residual activity of 2,4-D when transplants land directly in holes present in plastic mulch at the time of application. The relationship of dicamba with plastic mulch is complex as the herbicide cannot be easily removed by rainfall. Thus, dicamba should not be included in a weed management system in plasticulture vegetable production.

Chromatic Validation of Herbicides Used in Vegetable Production

“…Both herbicides were below the respective limit of detection by 18 days after application. Using similar sampling, processing, and analytical methods Hand et al [56] reported glyphosate to have a half-life of 2.2 days when applied to the surface of plastic mulch. These findings correlate to the amount of rainfall received, which given the water solubility of both glyphosate and ammonium-glufosinate was the most influential factor in dissipation (Figure 11).…”