Comparison of Generic and Proprietary Aquatic Herbicides for Control of Invasive Vegetation : Part 2. Emergent Plants

Aquatic herbicides are one of the most effective and widespread ways to manage nuisance vegetation in the US After the active ingredient is selected, often there are numerous proprietary and generic branded products to select from. To date, limited efforts have been made to compare the efficacy of brand name and generic herbicides head to head; therefore, at tot al of 20 mesocosm trials were conducted to evaluate various 2,4 -D, glyphosate, imazapyr, and triclopyr products against alligatorweed (Alternanthera philoxeroides (Mart.) Griseb.), southern cattail (hereafter referred to as cattail, Typha domingensis Pers.), and creeping water primrose (hereafter referred as primrose, Ludwigia peploides (Kunth) P.H. Raven). All active ingredients were applied to foliage at broadcast rates commonly used in applications to public waters. Proprietary and generic 2,4 -D, glyphosate, imazapyr, and triclopyr were efficacious and provided 39 to 99% control of alligatorweed, cattail and primrose in 19 of the 20 trials. There were no significant differences i n product performance except glyphosate vs. alligatorweed (trial 1, Rodeo vs. Roundup Custom) and glyphosate vs. cattail (trial 1, Rodeo vs. Glyphosate 5.4). These results demonstrate under small -scale conditions, the majority of the generic and proprietary herbicides provided similar control of emergent vegetation, regardless of active ingredient

Comparison of generic and proprietary aquatic herbicides for control of invasive vegetation; part 3 : submersed plants

Herbicide selection is key to efficiently managing nuisance vegetation in our nation’s waterways. After selecting the active ingredient, there still remains multiple proprietary and generic products to choose from. Recent small-scale research has been conducted to compare the efficacy of these herbicides against floating and emergent species. Therefore, a series of mesocosm and growth chamber trials were conducted to evaluate subsurface applications of the following herbicides against submersed plants: diquat versus coontail (Ceratophyllum demersum L.), hydrilla (Hydrilla verticillata L.f. Royle), southern naiad (Najas guadalupensis (Sprengel) Magnus), and Eurasian watermilfoil (Myriophyllum spicatum L.); flumioxazin versus coontail, hydrilla, and Eurasian watermilfoil; and triclopyr against Eurasian watermilfoil. All active ingredients were applied at concentrations commonly used to manage these species in public waters. Visually, all herbicides within a particular active ingredient performed similarly with regard to the onset and severity of injury symptoms throughout the trials. All trials, except diquat versus Eurasian watermilfoil, resulted in no differences in efficacy among the 14 proprietary and generic herbicides tested, and all herbicides provided 43%–100% control, regardless of active ingredient and trial. Under mesocosm and growth chamber conditions, the majority of the generic and proprietary herbicides evaluated against submersed plants provided similar control.

Effect of Herbicide-Treated Irrigation Water on Four Vegetables

Bodies of water that are treated with herbicides for aquatic weed control are often used as a source of irrigation water by landowners near the water body, but there is little information regarding the effects of experimental aquatic herbicides on common garden plants. Therefore, the goal of these experiments was to identify phytotoxicity of four herbicides on vegetables frequently cultivated by home gardeners. Sweet pepper, zucchini, tomato, and bush bean were irrigated with water containing bispyribac-sodium, quinclorac, topramezone, and trifloxysulfuron-sodium to identify the herbicide concentrations that damage these garden vegetables. Experiments were conducted during 2009 and repeated in 2010. Plants were irrigated four times during an 11-d period with the equivalent of 1.27 cm of treated water during each irrigation, then irrigated with well water until they were harvested 41 d after the first herbicide treatment. Values of the concentration of herbicide expected to reduce treated plants by 10% compared with control plants (EC10) were calculated from components of nonlinear regression. Analysis of visual quality and dry weight data revealed that bush bean was the most sensitive of the vegetable plants to bispyribac-sodium, trifloxysulfuron-sodium, and topramezone, whereas the species most sensitive to quinclorac was zucchini. Exposure of bush bean to 7.1, 0.9, and 1.2 parts per billion (ppb) of bispyribac-sodium, trifloxysulfuron-sodium, and topramezone, respectively, would be expected to cause 10% reductions compared with control plants, whereas exposure of zucchini to as little as 11.0 ppb of quinclorac would be expected to cause a 10% reduction in dry weight.

Evaluating the Potential for Differential Susceptibility of Common Reed (Phragmites australis) Haplotypes I and M to Aquatic Herbicides

Common reed (Phragmites australis) is an invasive perennial grass in aquatic and riparian environments across the United States, forming monotypic stands that displace native vegetation that provides food and cover for wildlife. Genetic variation in global populations of common reed has given rise to two invasive haplotypes, I and M, in the United States. Our objectives were to (1) determine if any differences in herbicide efficacy exist with respect to common reed haplotypes I and M and (2) screen for other labeled aquatic herbicides that may have activity on common reed haplotypes I and M, most notably imazamox and diquat. A replicated outdoor mesocosm study was conducted in 1,136-L (300-gal) tanks using haplotypes I and M of common reed. Restriction fragment length polymorphism methodologies were used to verify the identification of I and M haplotypes used in this study. Diquat at 2.2 (1.9) and 4.5 (4.0) kg ai ha−1 (lb ai ac−1), glyphosate at 2.1 (1.8) and 4.2 (3.7) kg ae ha−1 (lb ae ac−1), imazamox at 0.6 (0.5) and 1.1 (0.9) kg ai ha−1 (lb ai ac−1), imazapyr at 0.8 (0.7) and 1.7 (1.5) kg ai ha−1 (lb ai ac−1), and triclopyr at 3.4 (3.0) and 6.7 (5.9) kg ae ha−1 (lb ae ac−1) were applied to the foliage of common reed. After 12 wk, no difference (P = 0.28) in herbicide tolerance was seen between the two haplotypes with respect to biomass. The 4.2-kg ae ha−1 rate of glyphosate and the 0.8- and 1.7 kg ai ha−1 rates of imazapyr reduced common reed by > 90% at 12 wk after treatment (WAT). Imazamox at 0.6 and 1.1 kg ai ha−1, and triclopyr at 3.4 and 6.7 kg ae ha−1 reduced common reed biomass (62–86%) at 12 WAT, though regrowth occurred. Diquat did not significantly reduce biomass by 12 wk. Glyphosate and imazapyr were the only herbicides that resulted in > 90% biomass reduction and corroborate control from previous studies.