Physical Control of Nonindigenous Aquatic Plants in Emerald Bay, Lake Tahoe, CA

Abstract

Establishment of nonindigenous (NI) aquatic plants in the nearshore regions of freshwater ecosystems has resulted in environmental degradation, recreation concerns, economic impacts, and substantial management challenges. To reduce these undesirable effects, NI aquatic plants are often targeted for removal or control by management agencies, but the efficacy of implementation is often not documented or sustained. In this study, we developed a management plan to completely remove all NI plants from Emerald Bay, Lake Tahoe, CA, using only physical control techniques. Management plan priorities were based on previous research and lessons learned, including the need for (1) integrated weed management using multiple physical control techniques, (2) a large initial treatment investment, (3) ongoing early detection and rapid response, (4) detailed ecological monitoring, and (5) a long-term commitment to annual maintenance removal. Application of this management plan resulted in complete removal of all NI aquatic plants from Emerald Bay and substantial cost savings each year after the initial large investment. Annual maintenance removal and monitoring will need to continue as long as NI aquatic plants continue to enter Emerald Bay on boats and currents from other areas of Lake Tahoe.

Efficient and rapid control of Eurasian watermilfoil (Myriophyllum spicatum) by combining benthic mats and hand pulling

“…The same process was repeated in 2021 from May 21 to June 1 (435 accumulated degree days >0 C by May 21), at the same locations, although the quadrat may have settled in slightly offset locations between 2020 and 2021. Stem density data collected in 2021 were compared with those of 2020 with paired-sample Wilcoxon signed-rank tests, because the data were not normally distributed (Scherrer 1984).…”

“…In 2018, for example, monitoring resulted in the rapid detection and removal of 60 M. spicatum individuals, even though no specimen had been detected in the previous 4 yr (Hauge Brueck Associates, LLC 2020). The main conclusions of Shaw et al (2016) are (1) a large initial investment is required, (2) costs decrease over time if the initial stage is successful and followed by annual monitoring, (3) physical techniques can reduce the biomass of an invasive plant relatively quickly if adequate effort is made, and (4) focusing control efforts on a small number of sites is more effective than thinly stretching resources over a broad area.…”

“…The plant is manually extracted by divers, taking care to remove not only the stems, but also the shallow root system. The harvested material is then brought to the surface in bags or using a suction device (Bailey and Calhoun 2008; Boylen et al 1996; Eichler et al 1993; Kelting and Laxson 2010; Shaw et al 2016). Large-scale hand-pulling campaigns have been undertaken at Lake George and Upper Saranac Lake in New York State.…”

Invasive Smooth Cordgrass (Spartina alterniflora) Eradication and Native Crab Recovery

“…An integrated regime for invasive plant control is a treatment in which one control method is followed by another. An increasing number of recent studies have shown that an integrated regime has higher control efficacy than a single method (Hammond 2001;Hedge et al 2003;Patten 2002Patten , 2003Roberts and Pullin 2007;Shaw et al 2016;Strong and Ayres 2016;Wang et al 2006). For example, some studies have found that mowing followed by application of glyphosate can inhibit the growth and infestation of invasive species of the genus Spartina (cordgrass), more than when either method is used alone (Hedge et al 2003;Patten 2002Patten , 2003Wang et al 2006).…”

“…The high control efficacy of an integrated regime is believed to occur because such regimes incorporate dual treatments (Hammond 2001;Hedge et al 2003;Shaw et al 2016;Wang et al 2006). However, while many studies have indicated the importance of different types of methods on the control efficacy of an integrated regime, the effects of the intensity of an integrated regime and the interval between the applied methods have been mostly ignored and are still unclear.…”