Evaluation of herbicides for control of Eurasian watermilfoil and sago pondweed
Date
2010
Authors
Vassios, Joseph D. (Joseph Daniel), author
Nissen, Scott Jay, advisor
Ward, Sarah, committee member
Shaner, Dale L. (Dale Lester), committee member
Journal Title
Journal ISSN
Volume Title
Abstract
The aquatic species Eurasian watermilfoil (Myriophyllum spicatum) and sago pondweed (Stuckenia pectinata) can act in an invasive manner, and when present can negatively impact wildlife habitat. Eurasian watermilfoil is a submersed perennial noxious weed species that is widespread across the United States. Sago pondweed is a submersed perennial species that is a native to all 50 states. Although sago pondweed is a native, it thrives and can become troublesome in irrigation canals. Experiments were conducted to evaluate herbicides to control both species. Imazamox is a newly registered aquatic herbicide that can be used to control Eurasian watermilfoil. Three laboratory experiments were conducted to examine the response of Eurasian watermilfoil to imazamox. 14C –imazamox was used to evaluate imazamox absorption rate, the influence of external imazamox concentration on absorption, imazamox desorption when plants were transferred to clean water, and imazamox absorption. Imazamox absorption by Eurasian watermilfoil was low. The weed absorbed only 0.5% of the herbicide applied 24 HAT, and reached a maximum of 0.97% 72 HAT. External concentration affected imazamox absorption, where plants absorbed 1.05 g per plant at a treatment concentration of 200 μg L-1, while at 800 μg L-1 absorption was 4.06 μg per plant. The percent of applied imazamox absorbed was the same regardless of the external concentration, indicating that absorption was the result of simple diffusion driven by a concentration gradient. Desorption after plants were placed in clean water was rapid, reaching equilibrium by 12 hours with 46% of absorbed imazamox having moved into the surrounding water. The metabolism study indicated that 144 HAT; 69.04% of absorbed 14C-imazamox was found in the bound fraction, 11.52% as soluble metabolites and 21.44% remained as imazamox. In addition to laboratory experiments, three whole lake treatments were applied and imazamox dissipation was monitored. Three greenhouse experiments on sago pondweed were conducted to evaluate herbicide control when applied pre-emergence to a soil surface simulating a dewatered irrigation canal treatment. Herbicides evaluated included imazamox, imazapyr, fluridone, penoxsulam, flumioxazin, pyroxasulfone, dimethenamid, and metolachlor. In addition to herbicide control, the effect of incorporation using simulated rainfall was evaluated. Rainfall incorporation did not have a significant effect, and all treatments resulted in a biomass reduction on 70% or greater when compared to the untreated control. In addition to greenhouse studies, four field studies were conducted. Herbicide residues were quantified in canal sediments and canal water for all sites.
Description
Department Head: Thomas Holtzer.