Comparing alternative non-selective herbicides in Oregon and New Mexico

Authors: Mattox, Clint; BECK, LESLIE - New Mexico State University; STOCK, TIM - Oregon State University; LEINAUER, BERND - New Mexico State University; KOWALEWSKI, ALEX - Oregon State University

Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/16/2024
Publication Date: 11/13/2024
Citation: Mattox, C.M., Beck, L., Stock, T., Leinauer, B., Kowalewski, A. 2024. Comparing alternative non-selective herbicides in Oregon and New Mexico. Weed Technology. 38. Article e91. https://doi.org/10.1017/wet.2024.78.
DOI: https://doi.org/10.1017/wet.2024.78

Interpretive Summary: When it becomes necessary to renovate a lawn, non-selective herbicides are often used to terminate the existing vegetation, with glyphosate as a common choice for this purpose. When legislation or other pressures oblige landscape managers to choose alternatives to glyphosate, there is little research available on the efficacy of products currently sold as non-selective herbicides. This current research set out to test ten non-selective alternative herbicides with the goal of terminating an existing lawn that was contaminated with weeds in Corvallis, Oregon and Las Cruces, New Mexico. Applications were applied four times in Corvallis and five times in Las Cruces every two weeks in the spring. None of the treatments successfully terminated an established lawn in either location. These findings suggest that the application rates, frequencies, or timings tested in this research will not satisfactorily terminate a lawn under similar circumstances. One interesting finding, however, was that grasses and broadleaves exposed to the herbicides expressed different sensitivities, suggesting that future studies focusing on selective control is warranted. Specifically, the data suggests that some alternative herbicide treatments were more impactful in injuring dicot plants than monocots, especially in New Mexico where the dominant monocot was bermudagrass. This may indicate the possibility of spot-spraying dicot-specific weeds within a desirable turfgrass landscape with minimal and temporary discoloration of the turfgrass, especially stoloniferous and rhizomatous grass varieties like bermudagrass. Finally, even though none of the treatments successfully terminated the vegetation after four or five applications, that does not mean that they would be ineffective on less mature plants or with more applications; however, future research is needed to help clarify this question.

Technical Abstract: Alternatives to traditional chemical herbicides are being considered by municipalities for suppressing weeds and vegetation, although only limited efficacy research is available. A field experiment took place in Corvallis, Oregon and Las Cruces, New Mexico to quantify and compare the effects of repeated applications of ten non-selective herbicides needed to terminate a lawn. Four applications were made every two weeks starting on 15 April 2022 in Corvallis and five applications were made every two weeks starting 26 May 2022 in Las Cruces. Data collected included percent green cover over time calculated using an area under percent green cover progress curve (AUPGCPC), percent green cover at the conclusion of the experiment, and the change in monocot and dicot density over the course of the experiment. In Corvallis and Las Cruces, mint oil + sodium lauryl sulfate + potassium sorbate treatment did not decrease AUPGCPC compared to water only. In Las Cruces, neither clove oil nor the combination of cinnamon oil + clove oil decreased AUPGCPC compared to water only. All other treatments resulted in a lower AUPGCPC compared to water only. At the conclusion of the experiment, the water only plots averaged 90% and 99% green cover in Corvallis and Las Cruces respectively. The only treatments with an average percent green cover less than 50% was a combination of ammoniated soap of fatty acids + maleic hydrazide (47% green cover) in Corvallis and pelargonic acid (38%) in Las Cruces, suggesting that more applications would be needed to terminate the lawn under similar circumstances. The change of monocot and dicot densities over the course of the experiment indicated that some of the products tested may be more sensitive to dicots, or in some cases monocots, suggesting a potential for future selective herbicide research in certain locations and climates.