Influence of Surfactants and Ammonium Sulfate on Glyphosate Phytotoxicity to Quackgrass (Elytrigia repens)

Abstract

Field and greenhouse experiments were conducted to investigate the influence of two cationic alkylamine surfactants, three nonionic surfactants, and ammonium sulfate on the performance of glyphosate (isopropylamine salt) against quackgrass. In the field experiments, the reinfestation of quackgrass in the year after treatment was zero or negligible in all plots that received the recommended rate of glyphosate (1.44 kg ae/ha). At one-fourth of the recommended rate (0.36 kg ae/ha) the glyphosate-adjuvant combinations also severely inhibited the reinfestation of quackgrass. At the low herbicide rate and without ammonium sulfate, lipophilic surfactants were less effective than more hydrophilic surfactants. In the greenhouse experiments, the glyphosate doses giving 50% response (ED50) were determined. Ranking of the surfactants according to the ED50for glyphosate demonstrated a similar result to that observed in the field experiment. Ammonium sulfate added to the glyphosate-surfactant combinations reduced the ED50for glyphosate 5-fold. The field and greenhouse experiments demonstrated that two hydrophilic nonionic surfactants enhance glyphosate efficacy against quackgrass to the same extent as the hydrophilic cationic tallowamine surfactant. These two nonionic surfactants have a relatively low toxicity to non-target organisms and may substitute the more toxic alkylamine surfactants.

Foliar-Applied Glyphosate Substantially Reduced Uptake and Transport of Iron and Manganese in Sunflower (Helianthus annuus L.) Plants

“…The complexing action of glyphosate in roots is probably the main reason for the marked depression in root-to-shoot transport of Mn and Fe by glyphosate ( Figure 2). De Ruiter et al (35) showed that glyphosate reacts with Mn, Fe, and other cations present in the xylem sap of quack grass plants. Recently, Kremer et al (7) showed that glyphosate translocated from treated leaves to roots was then released into the rhizosphere at high amounts (up to 1 µg per plant).…”

Glyphosate Efficacy of Different Salt Formulations and Adjuvant Additives on Various Weeds

“…Glyphosate is usually applied with ammonium sulfate (AMS) in order to reduce water hardness and enhance herbicide activity [54,55]. More specifically, common cations, such as sodium (Na + ), potassium (K + ), magnesium (Mg 2+ ), calcium (Ca + ), iron (Fe 2+ or Fe 3+ ) and zinc (Zn 2+ ), bind strongly to glyphosate negatively charged molecules, and form salts that are not readily absorbed by plants [35,56].…”

“…In the same study, it was shown that low spray volumes also maximized glyphosate efficacy, even in the presence of AMS, through high herbicide concentrations in the spray deposit and overcoming of the antagonistic salts. De Ruiter et al [55] indicated that ammonium sulfate added to glyphosate-surfactant combinations reduced significantly ED 50 values for glyphosate. Moreover, De Ruiter and Meinen [71] found that the absorption of glyphosate by protoplasts, isolated from quackgrass (Elytrigia repens L.), was higher when ammonium sulphate was applied.…”

Plants as sources of cations antagonistic to glyphosate activity

“…AMS can also improve the activity of glyphosate when applied in deionised water. It is important to note that the degree of response was dependent on species 2, 9, 10. This suggests that additional sources of cations, other than in spray application water, are involved in glyphosate antagonism.…”

“…Glyphosate absorbed by the plant may also interact with cations in the cuticle and cell wall 10, 16, 17. This paper investigates the interactions of glyphosate, cations and AMS both on and within the plant.…”