Knotweed Management Strategy at the Watershed Scale in Vermont

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Knotweed Management Strategy at the Watershed Scale in Vermont

Prepared by:

Raina Brot-Goldberg

Lily Calabrese Amy Davis

Flore Costume

Olivia Lukacic

Ashlin Treadway

Prepared for: Robert Hyams and Vermont River Conservancy

University of Vermont

ENSC 202: Spring 2016

Acknowledgements

We would like to thank Robert Hyams from the Vermont River Conservancy for providing us with this opportunity and for his supervision during the process. Thank you to Kimberly Hagan for her assistance with inventive management practices. And thanks to William Bowden, our professor and commander, for his guidance along the way.

Table of Contents

Executive Summary

Introduction and Background

Methods/Approach

Findings

Mechanical Control

Chemical Control

Biological Control

Recommendations

Site Susceptibility

Classifying Infestation Severity

Field Analysis

Spatial Distribution Analysis

Future Recommendations

Literature citation

Appendix I. Prevention Measures

Appendix II: Japanese Knotweed Infestation Scale and Datasheet

Appendix III: Integrated Management Guidelines for Knotweed Removal

Appendix IV. Creative Ideas

Executive Summary

Invasive species are known to cause vast amounts of ecological and economic damage around the world. Japanese knotweed is no exception. With its ability to spread incredibly quickly and inhabit almost any area, controlling this weed is not an easy task. Knotweed is able to rapidly invade and outcompete native plants, effectively destabilizing the soil structure. This is of most concern in riparian areas because adequate soil structure is imperative for bank stability. In this report, we discuss the best chemical, biological, and mechanical methods for managing and removing knotweed. We discuss different land characteristics that affect the susceptibility of a site being invaded by knotweed in the future. We suggest a grading scale classifying knotweed infestation based on its impacts on ecology and effects to human value on the landscape as well as the feasibility of its removal. We also discuss theoretical methods of how one might determine the scaling of the different damage levels of these impacts and the level of knotweed infestation in an area. For our proposed management plan, we take into consideration the land use (agricultural, urban, or wooded), and the infestation level (none, low, moderate, or high), to determine which management practices would be best in each scenario. Finally, we touch on possible ways to limit the spread of knotweed and suggest inventive management strategies for the future.

Introduction and Background

Like many other aggressive non-native invasive, Japanese knotweed (Fallopia japonica) presence in the United States is cause for environmental concern. The species is commonly found along waterways, threatening the ecological capacity of riparian ecosystems. By forming dense monoculture patches, the knotweed outcompetes and blocks native flora and fauna from growing and dispersing (Maguire et al. 2008). Even though the rhizome structure is extensive, the roots do very little to stabilize soil and prevent against erosion compared to native species (Anderson 2012).The reason for this is that the knotweed root system consists of mainly just one large tap root, which instead of stabilizing the soil like other, more intricate, root systems, ends up breaking apart the soil structure. This in turn has negative effects on the greater riparian ecosystem. Its spread threatens property, landscapes, and the populations of native species (Maguire et al. 2008).

Japanese knotweed is a plant species native to Japan, Korea, China, and Taiwan. It was introduced to North America in the late 1800s from Great Britain (Bailey 2000) as an ornamental species. According to the USDA, knotweed is categorized by both state and federal governments as an invasive plant that causes extensive damage to riparian and roadside habitats and is currently present in nearly all 50 states. Knotweed is especially prolific along river corridors, railroads, roadsides, and hedgerows.

Knotweed can grow in diverse community and soil types. The plant prefers acidic soil conditions (pH 4 to 7.4) (Locandro 1973). Knotweed can reproduce both sexually and vegetatively, spreading through rhizomes, within its native range (Smith et al. 2007). The main spread of invasive species is through vegetative growth (Smith et al. 2006). This plays a crucial role along waterways, where the transport of a small piece of rhizome downstream can create a new infestation. Knotweed eradication is extremely difficult and costly to control. Although this species has been found in Vermont, the problem has not been properly addressed or mapped. Site-level responses to knotweed alone are often not effective and a watershed level strategy is needed.

This report aims to inform and recommend control techniques for Japanese knotweed in Vermont’s riparian areas and waterways in the context of land use, ecological factors, and degree of infestation. Based on recommendations by Vermont River Conservancy (VRC) we have provided suggestions for mapping knotweed using GIS databases which along with a data sheet to characterize the severity of infestations on a site by site basis. Infestation levels influence the type of control technique applied based on the suite of options laid out below. This report contains a system to determine a site’s vulnerability to knotweed infestation and an integrated land management plan to decrease the abundance of knotweed, to prevent future infestations and restore ecosystem services in the presence of knotweed.

The main objectives are:

● Summarize and address the variables which impact a site’s potential to be resilient to invasion

● Create a document to quantify infestation levels

● Create a user-friendly guide that compiles a suite of management practices for knotweed to be applied/ recommended on a site-level basis

Methods/Approach

Data for our findings were collected through online searches and scientific databases (Web of Science, Science Direct etc.) to find best management strategies for knotweed. Kimberly Hagen from the University of Vermont (UVM) Agriculture extension was interviewed. Map data was obtained from the Vermont Center for Geographic Information and from the Vermont extension of iMapInvasives. Analysts from the Lake Champlain Basin Program and Nature Conservancy provided input for grading scale procedures. Robert Hyams from the VRC directed supervision.

Findings

Mechanical Control

Cutting and mowing have been suggestions for important conservation areas, but have not been proven to be effective in eradicating knotweed unless conducted over a several year time period (Mchugh 2006). Successful control has been observed in small isolated patches of knotweed after three consecutive years of uprooting the plant during the end of the summer season (Child and Wade 2000). It is possible for small knotweed patches to be hand dug which uproots stems and rhizomes, (Soll et al. 2006) but that can be inefficient and hazardous to floodplain sites. Digging can be effective because it can diminish root biomass and increase the stem to root ratio which would then allow a more effective follow up of herbicide treatment (Soll et al. 2006). In April (or depending on when the plant appears), hand cutting can be used, but must be done every 2-3 weeks, never letting the plant exceed over six inches in height. Knotweed plants must be cut as close to the ground surface as possible (Mchugh 2006). Cutting can also be done via mowing. Covering has been experimented with through the use geotextiles and plastic sheets; however, plastic is a less desirable option since it has been shown to disintegrate in field trials and could thus pollute the soil (Mchugh 2006). Geotextiles can be either woven or nonwoven and are encouraged in areas that inhibit the use of pesticides (Oregon TNC 2005). The use of geotextiles combined with intensive maintenance has shown some promise for control (Mchugh 2006). However, use of this control must be evaluated for use on flood banks since plant life is smothered (both invasive and native) underneath the covering. Using one mechanical control is not 100% effective at eradication and other control methods should be considered and supplemented into a control rotation when needed.

Chemical Control

Chemical controls are currently implemented through the use of herbicides and through various other methods which are site and context dependent. Glyphosate, commonly known as Roundup, is the most common herbicide applied to knotweed infestations (Hagen and Dunwiddie 2008). Application via stem injections have resulted in short-term dieback for low density and small diameter stems (Hagen and Dunwiddie 2008). A concern to this approach is the possibility that after injection, some glyphosate may “leak-out” of knotweed roots/rhizomes and remain active in coarser sandy and gravelly soils (Oregon TNC 2005). Foliar application of glyphosate is more commonly used as a control method and can reduce knotweed stems by 70-90% over time (Soll et al. 2006). Foliar sprays are more common due to its low cost and overall efficiency in time and effort. The wiping method can be used in moderate stands and is an option for those that do not want any risks associated with chemical drift. Imazapyr, another phloem-mobile herbicide have been proven to be effective on knotweed infestations and was found to be more effective in controlling knotweed than glyphosate (Bashtanova et al. 2009). It also has a lower rate of decomposition thus it is deemed safer to use near waterways than other herbicides (Soll et al. 2006). Herbicides should be used for severe infestations since they do pose environmental risk. Certain laws prohibit the use of herbicides in riparian areas and must be consulted before any application is done. Chemical and mechanical controls are usually partnered together.

Biological Control

Biological control is the use of an organism as a suppressant for a plant or animal pest. The field of biological control research is expanding as agricultural pesticides are causing environmental concerns and pesticide resistance in many pests. Though biological control can be an effective, sustainable approaches to dealing with invasive or native pests, there are several factors to consider before committing to any one biological control agent. An in-depth knowledge of the pest organism’s life cycle, habitat range, and natural predators is required to effectively choose natural enemies that may be of interest. There are several case studies that show unsuccessful outcomes and/or detrimental effects of the introduction of biological control agents due to nontarget effects (Louda 2002). Kimberly Hagen, a grazing specialist through UVM extension, has found success with Vermont farmers at reducing knotweed biomass by flash grazing cows and other ruminants. Flash grazing is the practice of briefly grazing an area to reduce a specific forage resource. The use of cows as biological control agents pose lower risk than classical biological control, and is much more cost effective and attainable in Vermont. Flash grazing reduces the risk of soil compaction, erosion, and overgrazing along riverbanks compared to long term grazing, and can show significant decrease in knotweed spread if done over several seasons.

Recommendations

Site Susceptibility

Japanese knotweed is able to grow in a wide variety of places, including both rural and urban areas. It grows best in full sun, preferring open spaces, but it is also able to tolerate full or partial shade. Japanese knotweed prefers soils with higher moisture content, such that would be found in riparian or wetland environment. Knotweed can also be found in many types of disturbed areas such as along the sides of roads, in old homesteads, and along the edges of forests or woodlands. It is also able to survive in extreme climates (including volcanic plains), in heavily polluted areas, and where the soil contains high levels of heavy metals (Anderson 2012). Japanese knotweed is also able to grow where the soil has a very high salinity (Richards et al. 2008). A case study has found that in more urbanized communities there is a lesser chance of finding knotweed infestations (Barney et al. 2008). The study also found a positive correlation between mean precipitation and length of adjacent highways and knotweed distribution (Barney et al. 2008). These variables could potentially be used in order to assess a site’s ability to be a suitable habitat for Japanese knotweed and help prioritize which sites we should be most concerned about allowing Japanese knotweed to spread into. Predicting which areas are likely to be susceptible to a knotweed invasion in the future is difficult and prevention measures (see Appendix I) should be taken to reduce infestation risks.

Classifying Infestation Severity

Field Analysis

Knotweed is already established in Vermont and based on the inherent risks associated with its spread, efforts to control it should be taken before the infestation progresses further. A grading system will allow users to determine the extent at which knotweed is present, and help evaluate which sites have high levels of risk associated with it. We define risk as any element of knotweed invasion which alters or undermines the composition, stability, and ecological functions of the natural community. The risk is characterized by the structural, environmental, and human health impacts at each site (See Appendix I).

The Michigan Department of Environmental Quality (DEQ) has constructed a user guide which uses a rating system to assign a numerical value to each of the risk sub-categories for Phragmites infestations. We used this as an example for our knotweed grading scale document, which would benefit users in the field. It quantifies the severity of an infestation based on the sum total of the individual scores for infestation size, local abundance, property ownership, land usage, condition of neighboring waterways, and the presence of rare species. This number tells the observer whether or not the site in which they are monitoring should be marked as a high, medium or low infestation level. Higher scores, signifying a high infestation level may be difficult to control and need more intensive management and often should be treated with a higher priority. Lower scores, signifying a low infestation level, may be smaller scale infestations. However it is important to look at the overall context of all sites needed to be treated because prevention and intensive removal of low levels of infestation might be more effective then attempting high-level eradication. The format of this grading system is subjective, and can be designed to suit the needs of the project.

Our proposed grading scale should be seen as an example and jumping off point for a system that needs further refinement. The general lack of research done on knotweed infestations and site susceptibility meant that our grading scale could be debated and changed based on the users values. The form should be taken into the field as a data sheet to understand a particular infestation. The six criteria listed are important at understanding the context of the area. Infestation size/density gives the user an idea of what control methods are appropriate and therefore the larger sites and this higher scores require more in depth approaches. Local abundance looks at surrounding area to understand the larger picture of this site. This allows the user to understand if an infestation is isolated or part of a larger problem. Land ownership should be changed based on user objectives, however for our example we chose to view the problem from a larger management agency position. Therefore high use and high visibility areas are more critical to address then private land area. Surrounding land use is another characteristic that has high value association. Here agriculture and public parkland rank higher then developed or public natural resource land, although all land types are important to be managed. Agriculture poses a higher monetary risk with invasive infestation and public parkland has high use as well as high recreation and aesthetic value. It is also important to look at the site in context of the waterway that it is bordering. Drinking water and high quality water sources need more immediate attention to the effects that Japanese knotweed infestations can have over already impaired waterways. Lastly the site value can give priority for management needs. Sites that contain rare or underrepresented natural communities or species, or have high wildlife habitat should be treated with more urgency.

Spatial Distribution Analysis

Methods of identifying the spatial distribution of invasive weeds can be divided into two general categories: manual and remote sensing. Manual survey techniques include traversing the landscape to locate areas of infestation, making observations, and collecting data to quantify the scale of infestation. This could include taking stem counts or performing grid surveys, in addition to using handheld GPS devices to plot the coordinates of the infested sites. On small scale projects manual surveys can be a very useful tool to gather baseline data or track trends in the distribution and density of an infestation. However, for large scale projects manual surveying may not be the most practical.

Geographic Information Systems (GIS) can be used to analyze the landscape for greater manipulation and visualization of the data. It also gives users the ability to add additional data layers from other sources to create a map that best serves their goals. Methods of analyzing vegetation density come from the use of remote sensing. This information is gained by scanning the earth surface by plane or satellite. Observation systems can be either passive or active. Active systems utilize laser technology to bounce a beam off a surface and measure its return; this technology includes Sonar, Radar, and LiDAR. Passive systems require sunlight to be reflected instead; this includes all optical instruments, such as a camera (gisgeography 2016).