Lower concentrations of acetic acid still disrupt leaf surface structures causing plant death in Amaranthus palmeri
Abstract: Amaranthus palmeri has proved to be an economically damaging weed to many crops. Largely due to the overuse of traditional glyphosate-based herbicides, Amaranthus palmeri has evolved two strains: one resistant to glyphosate-based herbicides, GR A. palmeri, and one susceptible to glyphosate based herbicides, (GS) A. palmeri. It is important to understand if each strain responds to organic herbicide treatments that act on physical structures versus chemical pathways like the glyphosate-based herbicides. For this study, we hypothesized that lower concentrations of acetic acid could be used to control growth by disrupting leaf surface structures in both Glyphosate Resistant (GR) A. palmeri and Glyphosate Susceptible (GS) A. palmeri. To begin, we planted 10 pots of each Amaranthus palmeri strain. One pot served as the control, the others served as treatment pots. We planted black beans in the pots at the same time. The A. palmeri seeds emerged first (within three days of planting), we then treated the A. palmeri leaves daily to either a 5%, or 10% or 20% acetic acid solution. Micrographs were taken immediately before and 24 hrs after each treatment. Treatment with 5% acetic acid showed no significant results, but there were differences in leaf surface structures with 10% and 20% solutions. Differences in the physical structure of the foliar epicuticular wax showed that both strains responded by eroding the epidermal wax layer then deteriorating the cell post-application, and dying within 72 hours of initial treatment. The 10% acetic acid solution was most efficient. This all took place before the beans sprouted. Overall, the experiment showed that if caught early enough both strains of young Amaranthus palmeri may be treated with applications of 10% acetic acid. This should cause no harm to crops or the soil.
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