Angela G. Poovey

Small-Plot, Low-Dose Treatments of Triclopyr for Selective Control of Eurasian Watermilfoil

ABSTRACT Small-plot treatments of triclopyr were conducted on Lake Minnetonka and Lake Minnewashta, MN, during June 1998 to investigate the herbicides potential to selectively control Eurasian watermilfoil (Myriophyllum spicatum L.) at low doses. Applications were made on 1-ha plots with rates based on plot type: references (0 mg acid equivalent (ae)·L−1), protected plots (0.5 mg ae·L−1), semi-protected plots(1.0 mgae·L−1), and unprotected plots (1.5 mgae·L−1). Plot protection was a function of potential mixing in the water column. Herbicide residues were monitored to determine dissipation 1 through 72 h post treatment. Samples were analyzed with both a high performance liquid chromatography technique and an enzyme-linked immunosorbent assay method. Results from these two analytical techniques were compared, and found equivalent (R2 = 0.96). Triclopyr had a relatively short half-life for each treatment (3.5 hr at 0.5 mg ae·L−1, 2.9 hr at 1.0 mg ae·L−1, and 4.2 hr at 1.5 mg ae·L−1). At 8 weeks post treatment, there was a 30 to 45% reduction in Eurasian watermilfoil distribution. Greatest Eurasian watermilfoil control was achieved in plots using higher triclopyr rates. Frequency of native plants decreased by 24% in the untreated reference plot, 20% in the 0.5 mg ae·L−1 plot and 6% in the 1.0 and 1.5 mg ae·L−1 plots. Mean species per point, however, either increased or remained unchanged in seven of the nine treated plots. Decline of native plants may be partially attributed to the onset of fall senescence. Larger contiguous areas, higher triclopyr rates, and sequential applications may be required to enhance Eurasian watermilfoil control in small-plot, partial lake treatments.

AMEG: the new SETAC advisory group on aquatic macrophyte ecotoxicology

Introduction and backgroundPrimary producers play critical structural and functional roles in aquatic ecosystems; therefore, it is imperative that the potential risks of toxicants to aquatic plants are adequately assessed in the risk assessment of chemicals. The standard required macrophyte test species is the floating (non-sediment-rooted) duckweed Lemna spp. This macrophyte species might not be representative of all floating, rooted, emergent, and submerged macrophyte species because of differences in the duration and mode of exposure; sensitivity to the specific toxic mode of action of the chemical; and species-specific traits (e.g., duckweeds very short generation time).Discussion and perspectivesThese topics were addressed during the workshop entitled “Aquatic Macrophyte Risk Assessment for Pesticides” (AMRAP) where a risk assessment scheme for aquatic macrophytes was proposed. Four working groups evolved from this workshop and were charged with the task of developing Tier 1 and higher-tier aquatic macrophyte risk assessment procedures. Subsequently, a SETAC Advisory Group, the Macrophyte Ecotoxicology Group (AMEG) was formed as an umbrella organization for various macrophyte working groups. The purpose of AMEG is to provide scientifically based guidance in all aspects of aquatic macrophyte testing in the laboratory and field, including prospective as well as retrospective risk assessments for chemicals. As AMEG expands, it will begin to address new topics including bioremediation and sustainable management of aquatic macrophytes in the context of ecosystem services.

Concentration–Exposure Time Relationships for Controlling Sago Pondweed (Stuckenia pectinata) with Endothall

The submersed macrophyte, sago pondweed, frequently grows to nuisance levels in water conveyance systems throughout the western United States and can cause problems in lakes, reservoirs, and other water bodies. The liquid dipotassium and dimethylalkylamine salt formulations of endothall were evaluated for controlling sago pondweed using short exposure times (3 to 24 h) under controlled environmental conditions (14 : 10 h light : dark; 21.5 C). Endothall treatments ranged from 1 to 10 mg ai/L (dipotassium salt) and 0.5 to 5 mg ae/L (dimethylalkylamine salt). Sixteen concentration and exposure time (CET) combinations were evaluated in each study. At 4 wk after treatment, all CET combinations significantly reduced shoot biomass (43 to 99%) of sago pondweed compared with the untreated reference. Reduction in shoot biomass was greater in plants that received higher herbicide doses and longer exposure times. In addition, more than half of the endothall CET combinations controlled sago pondweed by at least 90%, with some providing > 98% control. At the endothall CETs evaluated, regrowth of sago pondweed could occur after 4 wk, and some level of retreatment might be required to maintain plant control throughout the growing season. Results indicate that endothall shows promise as an alternative vegetation management tool in flowing-water environments. Nomenclature: Endothall, sago pondweed, Stuckenia pectinata (L.) Boerner PTMPE