Surfactant Effects on Glyphosate Efficacy

Abstract

Field and greenhouse studies were performed to examine the influence of various surfactants with glyphosate on whole plant efficacy. Relationships were examined between glyphosate phytotoxicity and surfactant properties, including ionic form, degree of ethoxylation, and hydrophobe composition. Cationic tertiary amine surfactants enhanced glyphosate performance in both field and greenhouse studies. Nonionic allinol and octoxynol surfactants were not effective in combination with glyphosate. In field studies, glyphosate efficacy increased with increasing surfactant ethylene oxide (EO) content. Soybean and velvetleaf responded similarly to glyphosate-surfactant spray applications, as both demonstrated significant linear and quadratic relationships between increasing surfactant ethoxylation and phytotoxicity, while common lambsquarters showed a significant linear relationship only. Cationic surfactants were evaluated in the greenhouse and a significant quadratic regression of glyphosate phytotoxicity to common lambsquarters on increasing surfactant ethoxylation indicated an optimum surfactant EO content of about 10 moles. Both tertiary and quaternary ethoxylated fatty amines were effective with glyphosate in decreasing common lambsquarters' fresh weight. Fatty amine hydrophobe composition did not correlate with glyphosate phytotoxicity to common lambsquarters.

Adjuvants and glyphosate activity

“…A comprehensive survey by Wyrill and Burnside35 on common milkweed ( Asclepias syriaca L) and hemp dogbane ( Apocynum cannabinum L) found that ethoxylated amines were generally more efficacious than ethoxylated nonionic surfactants. Similar findings were reported on velvetleaf and soybean ( Glycine max (L) Merr), which showed that cationic surfactants performed better than their nonionic counterparts, although there was some dependence on hydrophobe composition and degree of ethoxylation 36. The latter factor has been examined in more detail by Nalewaja et al 37 for primary alcohol ethoxylates on wheat, where both glyphosate activity and absorption improved with increasing HLB and thus EO content.…”

2,4-D Past, Present, and Future: A Review

“…Ethylene oxide (EO) content (-CH 2 CH 2 O-) was inversely related to 2,4-D uptake (Thompson et al 1996), and surfactants with EO of 5 had greater uptake (85%) in broad bean (Vicia faba L.) compared with EO 10 (61%) and EO 14 (50%) (Liu 2004). A lower EO value corresponds to a shorter EO chain and less polar surfactant molecule (Riechers et al 1995). Uptake of 2,4-D increased when including a C13/C15 (i.e., 13-or 15-carbon chain per molecule, where more carbons make the surfactant more hydrophobic) alkanol surfactant compared with a C10 alkanol, and uptake was minimally increased using an octylphenol adjuvant (Liu 2004).…”

“…However, it was not stated in this study whether or not an adjuvant was included in these tank mixes. Field and greenhouse studies have shown that cationic, tallow amine surfactants optimize foliar uptake and activity of glyphosate (Riechers et al 1995); as a result, it may be possible that these cationic surfactants also increase 2,4-D or dicamba uptake when applied in tank mixes, leading to the observed synergistic interactions in dicot weeds. Crop Safening with 2,4-D Tank Mixes.…”

Control of Glyphosate-Resistant and Glyphosate-Sensitive Giant Ragweed in Soybean with Adjuvant, Fomesafen, and Glyphosate Tank Mixtures

“…The Flexstar formulation of fomesafen contains a proprietary adjuvant, but as weeds become larger the label recommends the addition of a crop oil concentrate to help increase control. Fomesafen or a crop oil concentrate tank mixed glyphosate could be beneficial for giant ragweed control, but have also been shown to reduce the efficacy of glyphosate on other weed species (7,9,13,15). Thus, control of GR giant ragweed requires an adjuvant system that will maximize the efficacy of fomesafen while maintaining the activity of glyphosate on other weeds.…”