26 Jun 2024

Flowering Rush Control in Hydrodynamic Systems: Part 2: Field Demonstrations for Chemical Control of Flowering Rush

Abstract: A series of 10 water-exchange studies were conducted from 2019 to 2021 at two sites, Clover Island and Osprey Point, within the McNary Pool of the Columbia River on the Oregon-Washington border. Six of the studies incorporated a barrier curtain or bubble curtain, whereas the other four studies did not include any device to mitigate water exchange. Once annually, diquat aquatic herbicide was applied concurrently with rhodamine water tracing (RWT) dye at the Osprey Point site (2019–2021) to control flowering rush. An additional plot, Clover Island Reference, served as the nontreated control to the Osprey Point treatment plot. Pre- and posttreatment vegetation surveys were conducted in 2019, 2020, and 2021 to determine flowering rush control, treatment impacts to water quality, and nontarget species response. This study sought to (1) document the use of barrier curtains and bubble curtains as potential methods for reducing water exchange and increasing herbicide concentration exposure times within potential flowering rush treatment areas, (2) evaluate bulk water exchange and selective control of flowering rush under varying reservoir operations, and (3) use the results from these studies to provide guidance for managing submersed flowering rush infestations on the McNary Pool, Columbia River, and similar run-of-the-river impoundments.

18 Jun 2024

Initial Rearing, Release, and Establishment of Biological Control Agent Pseudophilothrips ichini to Control Brazilian Peppertree (Schinus terebinthifolia) in South Texas Ecosystem Restoration Projects

Abstract: Control of the invasive Brazilian peppertree (Schinus terebinthifolia) is a major cost component of US Army Corps of Engineers (USACE) ecosystem restoration (ER) projects in South Texas, specifically the USACE Galveston district (SWG) Resacas at Brownsville, Texas, ER Project. Biological control has been developed as a sustainable tool to lower long-term weed management costs. Although a biological control program for S. terebinthifolia has been in operation in Florida since 2019, no similar program existed in Texas until initiated by the Engineer Research and Development Center (ERDC) in 2020. Since 2021, the biological control agent Pseudophilothrips ichini has been reared at ERDC. This technical report details rearing, release, and establishment efforts from fall 2020 to spring 2023 to provide control of S. terebinthifolia in South Texas USACE ER project locations. Initial observations on impact and potential limitations to biological control in hot climates such as those of South Texas are also discussed.

7 Jun 2023

Investigating Minimum Exposure Time Requirements of Diquat for Flowering Rush (Butomus umbellatus) Control

PURPOSE: The purpose of this study was to investigate the minimum exposure time requirements for submersed treatments of diquat to effectively control flowering rush (Butomus umbellatus L.). Identifying these parameters will provide critical information for the operational management of this species in high water exchange scenarios.

31 May 2023

Small Plot Applications of Florpyrauxifen –Benzyl (Procellacor SC™) for Control of Monoecious Hydrilla in Roanoke Rapids Lake, NC

Abstract: Four demonstration plots were selected at Roanoke Rapids Lake, NC to evaluate water exchange and aqueous herbicide residues in stands of submersed aquatic vegetation (SAV) following treatment with rhodamine wt dye and florpyrauxifen-benzyl to control monecious hydrilla. Florpyrauxifen-benzyl (Procellacor™ SC) was applied in combination with Rhodamine WT (RWT) at two of the plots. Dye measurements and herbicide residue samples were collected at specific time intervals to draw comparisons between herbicide and RWT dye dissipation. The two additional plots served as reference plots to the treatment plots. Pre- and post-treatment vegetation surveys were conducted to evaluate monoecious hydrilla control and non-target species response. RWT dye and herbicide residue data indicated rapid water exchange was occurring with each treatment plot. As a result, florpyrauxifen-benzyl concentration and exposure times (CETs) towards monoecious hydrilla were not sufficient to achieve adequate control by 4 weeks after treatment (WAT). To reduce the impact of hydraulic complexity and improve herbicide efficacy, treatments should coincide with minimal reservoir discharge events to extend herbicide CET relationships. Evaluations of florpyrauxifen-benzyl on late season, mature plants may have impacted herbicide efficacy. Evaluations should be conducted earlier in the growing season, on young, actively growing plants, to discern potential differences in efficacy due to treatment timing and phenology. More information on herbicide concentration and exposure time relationships for monoecious hydrilla should be developed in growth chamber and mesocosm settings to improve species selective management of monoecious hydrilla in hydrodynamic reservoirs.

16 Sep 2022

Flowering Rush Control in Hydrodynamic Systems: Part 1: Water Exchange Processes

Abstract: In 2018, field trials evaluated water-exchange processes using rhodamine WT dye to provide guidance on the effective management of flowering rush (Butomus umbellatus L.) at McNary Dam and Reservoir (Wallula Lake, 15,700 ha). Additional evaluations determined the effectiveness of BubbleTubing (hereafter referred to as bubble curtain) at reducing water exchange within potential flowering rush treatment areas. Dye readings were collected from multiple sampling points at specific time intervals until a dye half-life could be determined. Whole-plot dye half-lives at sites without bubble curtain ranged 0.56–6.7 h. In slower water-exchange sites (≥2.6 h dye half-life), the herbicide diquat should have a sufficient contact time to significantly reduce flowering rush aboveground biomass. Other sites demonstrated very rapid water exchange (<1.5 h dye half-life), likely too rapid to effectively control flowering rush using chemical treatments without the use of a barrier or curtain to slow water exchange. At one site, the use of the bubble curtain increased the dye half-life from 3.8 h with no curtain to 7.6 and 7.1 h with a bubble curtain. The bubble curtain’s ability to slow water exchange will provide improved chemical control and increase the potential for other chemical products to be effectively used.

26 May 2022

Growth Assessments of Starry Stonewort (Nitellopsis obtusa) in Various Substrate Types for Large-scale Cultivation Studies

Purpose: The purpose of this study was to compare multiple substrate types to optimize cultivation conditions for the invasive macroalga Nitellopsis obtusa (Desv. in Loisel.) J. Groves, commonly known as starry stonewort. Large-scale cultivation will allow for tiered approaches to management evaluation research while minimizing the influence of confounding variables.

1 Oct 2021

Phenology of Competitive Interactions and Implications for Management of the Invasive Wetland Plant Alternanthera philoxeroides

Purpose: Phenological differences between invading plants and members of recipient communities may increase the success of invaders because of priority effects. Thus, the application of management when the invader has a phenological advantage (for example, early in the year) can benefit other species by increasing resource availability. This technical note summarizes results from a combination of field observations and a mesocosm experiment to explore whether phenological differences between the invasive wetland plant, alligatorweed (Alternanthera philoxeroides [Mart.] Grseb.), and resident species contribute to alligatorweed success. We documented over two years the early-season growth of alligatorweed and other species at 12 sites in Louisiana, USA. We then conducted a subsequent mesocosm competition experiment between alligatorweed and a common wetland emergent species, spotted lady’s thumb (Persicaria maculosa [L.] Small), over a full year to detect differences in timing of growth and competitive interactions under two fertilizer levels.

23 Sep 2021

Efficacy of Florpyrauxifen-benzyl for Eurasian Watermilfoil Control and Nontarget Illinois Pondweed, Elodea, and Coontail Response

Purpose: This research evaluated low concentrations and short exposure times of the recently registered aquatic herbicide florpyrauxifen-benzyl (4-amino-3-chloro-6-(4-chloro-2-fluoro-3-methoxyphenyl)-5-fluoro-pyridine-2-benzyl ester) on the target plant Eurasian watermilfoil (Myriophyllum spicatum L., hereafter referred to as EWM) as well as selectivity towards the nontarget submersed species Illinois pondweed (Potamogeton illinoensis Morong), elodea (Elodea canadensis Michx.), and coontail (Ceratophyllum demersum L.)

23 Sep 2021

Comparison of Generic and Proprietary Aquatic Herbicides for Control of Invasive Vegetation; Part 3: Submersed Plants

Abstract: 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.

17 Sep 2021

Evaluation of light limitation and depth on germinated seeds of two species of water chestnut cultured under experimental conditions

Abstract: This technical note describes the results of a mesocosm experiment to determine the light and depth limitations of growth chamber germinated seeds of two species of water chestnut (Trapa spp.) naturalized in the northeastern United States.