Invasive aquatic plants constantly threaten freshwaters and associated environs globally. Water resource managers frequently seek new control tactics to combat invasive macrophytes, especially when the availability of herbicides registered for submersed plant control is limited. The synthetic auxin herbicide, florpyrauxifen-benzyl, recently registered (2018) for aquatic site applications in the United States, has shown success in controlling several invasive aquatic weeds. Studies were conducted to evaluate responses of native and invasive submersed plants to florpyrauxifen-benzyl under growth chamber conditions to provide insight on the selectivity of varying herbicide concentrations in New Zealand. Florpyrauxifen-benzyl concentrations evaluated ranged from 0.01 to 107.86 µg ai L−1, encompassing the maximum use concentration (48 µg L−1) for submersed plant applications. Dose–response metrics indicated the New Zealand native species watermilfoil [Myriophyllum triphyllum Orchard] was highly sensitive to florpyrauxifen-benzyl following a 21-d static exposure, having a dry weight 50% effective concentration (EC50) value of 1.2 µg L−1. The invasive species oxygen-weed [Lagarosiphon major (Ridley) Moss] and Canadian waterweed (Elodea canadensis Michx.) were less sensitive, with dry weight EC50 values of 35.4 and >107.86 µg L−1, respectively. Brazilian waterweed (Egeria densa Planch.) was most tolerant to the tested concentrations, as EC50 values were not achieved. Overall, results indicate florpyrauxifen-benzyl demonstrates potential for controlling L. major, with further large-scale screening required to confirm control among field site applications. As the native species (M. triphyllum) was most sensitive to florpyrauxifen-benzyl compared with the invasive plant evaluated (I/N ratio indicated >31.3 times more sensitive), any targeted concentration used for invasive plant control for field applications would likely injure the native M. triphyllum plants. Future studies should investigate additional native and invasive species for management guidance and consider how exposure times influence plant response using similar florpyrauxifen-benzyl concentrations tested in the present study.

Increasing the air temperature from 20 to 32 C, the water temperature from 21 to 30 C, and the wind velocity from 0 to 8 km/h increased the loss of EPTC (S-ethyl dipropyl carbamothioate) from water applied through a sprinkler by 24 to 138%. Decreasing the water temperature from 21 to 10 C decreased the loss of EPTC by 35 to 50%. Decreasing the water pressure or nozzle size by 33% or doubling the herbicide concentration did not affect the percentage of EPTC lost.

The effects of soil temperature, moisture, and herbicide concentration on the rate of degradation of dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine) were measured in clay loam and sandy loam in the laboratory. In sandy loam, the rate of degradation increased with increasing temperature. In clay loam, the rate of degradation increased from 10 to 30 C and decreased at 40 C. Soil moisture content influenced the rate of degradation in the following order: 22>11>>2.2% (air-dry) for clay loam and 12.0 = 6.0>>0.5% (air-dry) for sandy loam. First-order half-lives ranged from 3.2 at 30 C to 47 weeks at 10 C in clay loam, and 2.3 at 40 C to 31 weeks at 10 C in sandy loam. Applications in 2 yr did not cause buildup of dinitramine in the field. A mathematical model was used in an attempt to correlate laboratory and field data.

Greenhouse studies were conducted to determine yellow nutsedge response to selective placement of a 5-cm layer of norflurazon-treated soil above, below, or above plus below pregerminated nutsedge tubers. Norflurazon at 1.68 kg ai/ha applied postemergence (POST) as a foliar, soil, or foliar plus soil treatment was also evaluated. Soil concentrations of norflurazon at 1.5 mg/kg (w/w) applied below or above plus below nutsedge tubers reduced yellow nutsedge shoot numbers at least 69%, shoot height at least 71%, shoot dry weights at least 77%, and root tuber dry weights at least 89%. Yellow nutsedge growth reduction with norflurazon was greatest when norflurazon was placed in the soil profile below or above plus below the yellow nutsedge tubers. Placement of norflurazon above yellow nutsedge tubers did not reduce shoot number, height, or dry weight until the foliar portion of plants were removed 39 d after treatment. POST application of norflurazon did not reduce initial yellow nutsedge shoot number regardless of application method. Foliar-only POST application of norflurazon was less effective for reducing numbers of emerged yellow nutsedge than application to soil only or soil plus foliage.