Commercial pest control companies as well as homeowners are currently searching for alternatives to the herbicide glyphosate due to negative press and changing consumer preferences. These non-selective alternatives are almost exclusively contact-action herbicides (no systemic activity) and the most common options (diquat, pelargonic acid, acetic acid, plant oils, etc.) have been shown to be effective on annual weeds when label directions are followed. However, labels on individual products often recommend a wide range of application rates (concentrations of the herbicide) and application volumes depending upon weed size, creating confusion for users in terms of what rate and/or application volume is needed for optimal control while keeping costs low. The objective of this research was to evaluate four glyphosate alternatives (acetic acid, caprylic capric acid, diquat, and pelargonic acid) at both high and low labeled application rates and at three different application volumes including 50, 100, and 200 gallons per acre (1.2, 2.3, and 4.6 gallons per 1,000 ft2) to determine how efficacy differed based on these different treatment variables. Two weed species including yellow nutsedge (Cyperus esculentus) and garden spurge (Euphorbia hirta) were used for the evaluation to observe differences between an annual broadleaf (spurge) and a perennial sedge species (yellow nutsedge). Plants were allowed to grow for approximately 6 weeks, at which time herbicides were applied. Data collected included visual control ratings at 1, 2, and 4 weeks after treatment (WAT) and shoot weights collected at 5 WAT. Results differed by weed species and herbicide and on different evaluation dates. For yellow nutsedge, application volume was the most common significant main effect with similar control being achieved at both high and low label rates when the higher application volumes were used. For garden spurge, application volume was mostly insignificant with the high rate providing more consistent control regardless of application volume. Results indicate that for larger or perennial weed species, higher application volumes are more critical to success, given that adequate and label rates are used, as they were needed to achieve more thorough coverage to contact more shoot biomass. In contrast, for the smaller prostrate growing garden spurge, rate was most important as thorough coverage was achieved at the lowest application volumes. This research begins to help us better understand these alternative herbicides and develop recommendations for the most effective and efficient use of these products in Florida landscapes.
