Thymus Praecox Creeping Thyme Albiflorus Veronica X (Alpina V
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1 Final Report Identification, Utilization and Maintenance of Weed Suppressive Ground Covers Along New York Highways for Vegetation Management Leslie A. Weston and Andrew F. Senesac With assistance provided by: Jennifer Allaire, Seok Hyun Eom, Roselee Harmon and Irene Tsontakis-Bradley Cornell University Department of Horticulture and Cornell Cooperative Extension Service of Suffolk County at Long Island Horticulture Research and Extension Center June 2004 Table of Contents Page Number Introduction 2 Field Experiment 1 3 Field Experiment 2 10 Field Experiment 3 16 Greenhouse Stress Experiments 18 Roadside Evaluations 24 Changes in Protocol 28 2 Introduction: The cost of vegetation management along New York State’s roads and highways results in expenditures of millions of dollars annually, for herbicides, mowing and hand labor in particular. New York State has been a leader in development of environmental policy for protection of its water and land resources for years. Recent public concern over the use of pesticides in municipal and state properties has resulted in the development of legislation since the year 2000, limiting municipal application of pesticides, including herbicides, in several locations across the state, including Suffolk and Nassau counties on Long Island, Westchester county and Erie county. Declining resources and an increased interest in management strategies with limited environmental impact have also reinforced the need to examine alternative strategies for vegetation management along New York State’s highway system. Effective alternative strategies could result in significant savings in terms of herbicide application, and further enhance their widespread adoption across the Northeast. To date, greatest vegetation management problems are encountered in highway medians and alongside roadways where guide rails are often encountered. Mowing is not always an option for weed management, especially under guide rails. Organic approaches for weed management including insect, pathogen and chemical application have been assessed in numerous landscape and a few roadside trials conducted by the authors, and have generally not been proven effective, with limited control observed (Bertin and Weston, 2003). In other studies conducted in recent years by the NY State DOT, trials involving landscape fabrics, mulching materials and certain organic products for weed suppression suggested that these alternatives were often expensive and not considerably effective for vegetation management along roadsides (NY State DOT reports). One potential option that has been underutilized in the U.S. and requires further consideration is the evaluation and utilization of weed suppressive, stress tolerant groundcovers which suppress annual and perennial weed infestations by providing a dense cover which competes for space, light, fertility, water and also inhibits weed growth by releasing natural herbicides, or allelochemicals from foliage or living root systems (Weston, 1996; Weston and Duke, 2003). Weed suppressive ground covers have been used effectively for years in orchards, vineyards, nurseries and vegetable fields. Less information exists about their utilization along roadsides in the temperate Northeastern U.S. In a site visit to Pennsylvania State University, we discovered that Pennsylvania DOT still considers use of crown vetch groundcovers for vegetation management along sloped roadsites, but in other states, this groundcover is considered less than optimal due to its ability to move offsite, unkempt appearance and difficulty to control. Fescues were also examined in Pennsylvania for use in roadside mixtures, with good results. In recent site visits to New Jersey, problems exist in development of high quality turf mixtures adapted to roadside conditions, including sandy soil sites, and enhanced vegetation management options are desired which would include selection of better adapted turfgrass mixtures for various state growing sites and optimal herbicide mixtures for effective management of difficult to control vegetation, including invasive species. Although the focus on environmental impact of herbicides in these states was less than in NY, roadside managers have expressed great interest in NY, PA and NJ locales in alternative, weed suppressive groundcovers, including newer cultivars of 3 turfgrasses, for lower maintenance inputs and achievement of better turf quality with reduced mowing requirements. Recent workshops conducted with NY State DOT personnel responsible for roadside vegetation management have also indicated great interest in alternative vegetation management strategies including selection of new groundcovers for roadside plantation (Weston, personal communication, 2004). This project was designed to select, evaluate and identify effective weed suppressive groundcovers, including herbaceous ornamental and grass species, which could be easily established under and adjacent to guiderails along NY highways, withstanding droughty conditions, infertile soils, winter road salts and other environmental challenges which might be encountered along roadsides. Experiments were performed from 2000-2003 in the field, laboratory and greenhouse research sites in 2 NY locations; Ithaca and Riverhead NY. In addition, roadside evaluation of selected groundcovers was performed at selected sites along NY State roadsides in 2003 in variable climatic and environmental conditions ranging from Long Island to upstate New York. Please note that all relevant data collected during the course of these studies will be presented in a large appendix file to the NY State DOT for future use. The quantity of data generated was considerable and due to the size of this dataset, we cannot present all of this in verbal form, but instead have chosen to present a summary document accompanied by a comprehensive data appendix. The following table (Table 1) summarizes where and when major studies were conducted during the course of this project: Field study 1 Field study 2 Field study 3 Stress Roadside groundcovers groundcovers fine fescues Evaluation of Evaluation groundcovers groundcovers Ithaca NY Ithaca NY Ithaca NY Ithaca NY Ithaca NY 2000-2002 2002-2003 2001-2003 2003-2003 2003-2004 Riverhead NY Riverhead NY Riverhead NY Riverhead NY 2000-2002 2002-2003 2001-2002 2003-2004 Summary of Results from Field Studies Conducted in 2000-2003: 1. Field study 1 Field plots containing 21 species in Ithaca NY and 26 species in Riverhead NY were initially transplanted in September 2000, using 3 replications per treatment. Treatments consisted of the following 1) groundcovers that were weeded to establish 2) groundcovers that were weeded throughout the experiment and 3) groundcovers that were not weeded at all. All plots were allowed to initially establish by performing one hand weeding in early spring 2001. In 2001 and 2002 monthly data analysis included weed numbers per plot, weed biomass, time required for weed removal, light penetration of groundcover canopy, visual density of groundcover at the soil surface, and height of groundcover. This data was collected to clearly monitor both groundcover performance once established, and natural weed infestations resulting over time in each groundcover treatment. The following table provides a list of the species examined in studies performed in Ithaca NY and Riverhead NY in 2000-2002. These are the original species 4 proposed in our initial project description, and no variation in this initial selection occurred. Table 2. List of species evaluated in Field study 1 conducted in Ithaca and Riverhead NY from 2000-2002. Genus Common Name Cultivar Alchemilla mollis Lady's Mantle Carex morrowii Sedge Ice dance Fragaria x Flowering Strawberry Lipstick Houstonia serpyllifolia Bluettes Hydrangea anomala Climbing hydrangea peteolaris Hypericum calycinum St. Jonhswort Hypericum moseranum St. Jonhswort Mix Tricolor Imperata cylindica Japanese blood grass Red Baron Lamiastrum galebdolon Yellow Archangel Herman's Pride Liriope spicata Liriope Leymus arenarius Blue Lyme Grass Blue Dune Lysimachia nummilaria Moneywort Aurea Mazus reptans Mazus Nepeta x faassenii Cat mint Walker's Low Phlox subulata Creeping Phlox Emerald Blue Phuopsis stylosa Phuopsis Sedum reflexum Sedum Blue Spruce Solidago sphacelata Dwarf Goldenrod Golden Fleece Thymus praecox Creeping thyme Albiflorus Veronica x (alpina v. alba x spicata) Speedwell Goodness Grows Vinca minor Vinca The species planted in Riverhead, Field Study 1, Fall 2000 were: Achillea tomentosa 'King Edward' Alchemilla mollis Arctostaphylos uva-ursi 'Pt. Reyes' Carex morrowii 'Ice Dance' Chrysogonum virginianum 'Pierre' Fragaria x (F. ananassa x Potentilla palustris) 'Lipstick' Houstonia serpyllifolia Hydrangea anomala 'Peteolaris' Hypericum calycinum Hypericum x moserianum Imperata cylindica 'Red Baron' Lamiastrum galebdolon 'Herman's Pride' Leymus arenarius 'Blue Dune'* Liriope muscari 'Royal Purple' Liriope spicata 'Majestic' Lysimachia nummularia 'Aurea' Mazus reptans Miscanthus sinensis Nepeta x faassenii 'Walker's Low' Phlox subulata 'Emerald Blue' 5 Phuopsis stylosa Sedum reflexum 'Blue Spruce' Solidago sphacelata 'Golden Fleece' Thymus praecox 'Albiflorus' Veronica x (alpina v. alba x spicata) 'Goodness Grows' Vinca minor. (*Note: We have found this species to be an aggressive spreader by rhizome. It is potentially weedy and/or invasive. It should be used with caution and only in sites where it can be contained.) A. Ithaca Results Species which did not overwinter: Five species including