Field Evaluation of Triclopyr (Garlon 3A) for Controlling Eurasian Watermilfoilin the Pend Oreille River, Washington

摘要

In an effort to evaluate the selective control of the exotic weed Eurasianwatermilfoil (Myriophyllum spicatum L.) and to assess the recovery of the native submersed plant community, a 6-ha river and 4-ha cove plot were treated with the herbicide triclopyr at application rates of 2.5 and 1.75 mg/f, respectively, in the Pend Oreille River, Washington, in August 1991. Water-exchange half-lives within the plots were measured using rhodamine wT dye (river, tin =20 hr; cove, tj/2 =52 hr), and triclopyr dissipation rates were also calculated (river, ti,2 = 19 hr; cover, ti2 =53 hr). Triclopyr concentrations were below proposed potable water tolerance levels (0.5 mg/f) within the river treatment plot by 3 days after treatment (DAT) (<0.01 to OAl mg/f), and 675 m downstream of that plot by 1 days after treatment (DAT) <0.01 to 0A7 mg/f. Following the cove treatment, triclopyr residues ranged from 0.12 to 0.29 mg/f by 7 DAT, and from <0.01 to 0.06 mg/f as close as 150 m downstream from the plot. Eurasian watermilfoil biomaaa was reduced by 99 percent in the treated plots at 4 weeks posttreatment, remained low 1 year later (river treatment, 28 percent of pretreat levels; cove treatment, 1 percent of pretreat levels), and was still at acceptable levels of control at 2 years posttreatment (river treatment, 47 percent of pretreat levels; cove treatment 24 percent of pretreat levels). The 4-week posttreatment efficacy results verified triclopyr concentration/exposure time relationships for controlling Eurasian watermilfoil developed under laboratory conditions. Nontarget native plant biomass increased 500 to 1,000 percent by I year posttreatment, and remained significantly higher in the cove plot at 2 years after treatment.