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Funded Project

Funding Program: IPM Enhancement Grants

Project Title: Survey of Pest Populations and Management Practices in Rain Gardens

Project Director (PD): Helen Kraus [1]

Lead State: NC Lead Organization: Department of Horticultural Science, North Carolina State University

Cooperating State(s): Virginia

Undesignated Funding: $30,000

Start Date: Mar-01-2015 End Date: Feb-29-2016

Pests Involved: weeds

Site/Commodity: urban landscapes

Area of Emphasis: rain gardens

Summary: Rain gardens serve aesthetic purposes as well, requiring significant plant and pest management inputs. Yet no comprehensive assessment of rain garden pest management needs or practices has been published. Weed control in rain gardens is particularly complex due to the frequent inundation and saturation events, and low organic matter and clay contents of typical rain garden substrates, resulting in concerns about herbicide movement into surface or sub-surface water. Additionally, it is unclear if residual herbicides would be useful tools in managing weeds in rain gardens. Laabs et al. (2000) reported that in wet, organic soils, the residual half-life for trifluralin, a herbicide commonly used in landscape management, was less than 1 day. Thus, rain garden maintenance professionals are hesitant to use herbicides. Only physical or mechanical methods of weed removal are recommended at this time. A search of the literature revealed no research reports or recommendations for weed control in rain gardens other than organic mulches. In some situations, mulches have been as effective as one to three applications of a non-selective herbicide (glyphosate) for short-term weed control (Roe et al., 1993). Yet, mulches alone are not sufficiently effective for long-term weed control in rain gardens, as evidenced by a recent survey of maintenance professionals in NC (not yet published) and inventory of ten rain gardens near Raleigh, over 32 annual and perennial weed species were identified. This project proposes to document pest and weed populations as well as pest management practices in professionally designed and installed rain gardens in NC and VA. Pest populations will be compared to site construction materials and methods, site conditions, garden plant health, and maintenance practices that may impact pest populations and management decisions. These data will provide the information required to better prioritize research and educational programs for rain garden installation and management, and will ensure that rain garden installations continue to serve as effective components in stormwater bioremediation. Objectives: Long-term outcome(s): Improved pest and weed management practices Phrase or sentence, condition change: A knowledge-based approach to pest and weed management depends on an understanding of the pests and weeds. Medium-term outcome(s): Improved pest management research and educational programs Phrase or sentence, action change: Research and educational programs will target the pest species and management issues of importance Short-term outcome(s): A survey of pest species and current management practices affecting pest control and plant health Phrase or sentence, learning change etc.: IPM based management practices depend upon understanding garden plant health and the pest species and the available management options.

Final Report:

Outputs This research project surveyed weed populations, ornamental plant health, presence of mulch, and substrate pH in seventy-four rain gardens across North Carolina and Virginia. The dates and cities for site surveys are listed below. City and State Date of Survey Weeds Sampled Number of Rain Gardens Sampled Herndon, VA July 2014 Warm season 1 McLean, VA July 2014 Warm season 1 Alexandria, VA July 2014 Warm season 1 Fairfax, VA July 2014 Warm season 2 Chantilly, VA July 2014 Warm season 2 Raleigh, NC June 2015 Warm season 30 Wake Forest, NC June 2015 Warm season 2 Apex, NC June 2015 Warm season 7 Elon, NC July 2015 Warm season 1 Greensboro, NC July 2015 Warm season 2 Charlotte, NC July 2015 Warm season 1 Huntersville, NC July 2015 Warm season 13 Cornelius, NC July 2015 Warm season 3 Cary, NC August 2015 Warm season 7 Wake Forest, NC December 2015 Cool season 2 Apex, NC December 2015 Cool season 6 Elon, NC December 2015 Cool season 1 Greensboro, NC December 2015 Cool season 2 Charlotte, NC December 2015 Cool season 1 Huntersville, NC December 2015 Cool season 13 Cornelius, NC December 2015 Cool season 3 Cary, NC December 2015 Cool season 7 Raleigh, NC January 2016 Cool season 27 Also, an online survey was constructed in order to gain an understanding from site managers about how rain gardens in landscapes are being maintained. However, making contact with the site managers and gaining feedback regarding their maintenance practices has been challenging and is still on going. Currently, no publications have resulted from this research project. However, once all of the data has been collected and analyzed there will be several types of publications created in order to inform the target audience (rain garden designers, installers, and maintainers). Educational materials will be developed to be included in extension training sessions. Also, an extension leaflet will be created to share online with the target audience and a peer-reviewed publication will be written. The Southern IPM Center and USDA NIFA will be acknowledged for their support in all publications produced from this research. Based on the results of this study thus far, most rain gardens are installed and then not maintained appropriately. Weed management is a major issue for rain gardens. Some rain gardens that have been maintained, and remain aesthetically pleasing, may not be using appropriate herbicides, likely due to a lack of education that landscape maintainers receive regarding rain gardens. Rain garden maintenance is not a component of most rain garden educational programing. As a result, rain gardens are maintained like other landscape features. Commonly, plants are not planted appropriately, get too large and shade other species within the rain gardens (personal observation). The data collected from this study will provide a service by informing future researchers of problematic weeds occurring in rain gardens in order to conduct studies to determine control options for the target audience (rain garden designers, installers, and maintainers). Also, the plant survival data and substrate pH data collected from this project will provide a service to the designers and installers by aiding them in proper plant selection to ensure success of the rain garden. An extension publication will be developed and shared with county extension offices. There has not been any additional funding secured using this project’s results or outputs. The data collected from this project is crucial in order to determine the correct weed management options for rain gardens. Funding will be sought from the Horticultural Research Institute in May 2016 to test herbicide applications in rain gardens to treat the weeds that were determined problematic in this research project. This application is not yet complete, thus the name of the project, dollar amount requested, and duration of anticipated funding is undetermined. Objective: Improved pest management research and educational programs. This objective has not been completed due to the need for data analysis. This objective will be completed after the end of this IPM Enhancement grant. No additional funding will be needed in order to complete this objective. *Surveyed weed populations, ornamental plant health, presence of mulch, and substrate pH in seventy-four rain gardens across North Carolina and Virginia. *Developed an online survey to gain an understanding from site managers about how rain gardens in landscapes are being maintained. *Once data analysis is completed several types of publications (extension leaflets, extension training course materials, and scientific peer reviewed article) will be written to inform the target audience (rain garden designers, installers, and maintainers). *Data collected from this study will inform future researchers of problematic weeds occurring in rain gardens in order to conduct further research to determine control options. *The plant survival and substrate pH data collected from this project will provide a service to the designers by aiding them in proper plant selection to ensure success of the rain garden. *Funding will be sought from the Horticultural Research Institute in May 2016 in order to conduct another research project to test herbicide application in rain gardens to treat the weeds that were determined problematic in this research project.

Outcomes Several types of baseline data have been collected throughout the duration of this project. The baseline data collected has provided insight into the most problematic weeds growing within rain gardens in North Carolina and Virginia. By collecting this baseline data, future projects will be able to focus on what weed management strategies are acceptable for use within rain gardens. Also, baseline data has been collected regarding plant health and substrate pH in rain gardens 10 years of age or older. This data will help to inform designers, installers, and maintainers of rain gardens on the selection of plants and potential plant success. Researchers and rain garden designers, installers, and maintainers will know the most problematic weeds in rain gardens. Also, the data collected regarding plant health and substrate pH in rain gardens will provide background knowledge so that proper plants are selected for utilization within the rain garden. This will help to ensure success and proper functionality of the rain gardens after installation. This information will be presented to the target audience through extension education courses and talks at horticulture professional meetings. Plants that tolerate low nutrient levels and pH and grow well in rain gardens have been identified and should be utilized by rain garden designers, installers, and maintainers. This will help to ensure aesthetic success and proper functionality of the rain gardens after installation. There are several condition outcomes that will result from the data collected throughout this research project. Economical conditions will be benefited from making proper plant selection based on the knowledge learned from the plant health and substrate pH collected through these surveys. This will help to reduce costs in maintaining rain gardens due plant replacement. Also, changes in environmental conditions will be impacted based on appropriate plant selection, which impact stormwater remediation once it enters the rain garden. Water quality will be protected with the recommendation of proper herbicides and education on the dangers of improper herbicide usage. *Baseline data have been collected and will provide insight into the most problematic weeds growing within rain gardens in North Carolina and Virginia. *Future projects will be able to utilize these baseline data to focus on weed management strategies acceptable for use within rain gardens. *Also, comparative data has been collected regarding plant health and substrate pH in rain gardens 10 years of age or older. This data will help to inform installers and maintainers of rain gardens on the selection of plants and potential plant success. * Economic returns will be increased with proper plant selections for rain gardens based on the knowledge gained from this research project by reducing costs from the removal of plant replacement. *Environmental conditions will be improved with appropriate plant selection, which impact stormwater runoff remediation within rain gardens and education on appropriate herbicide uses in rain gardens.

Report Appendices 3730865_0000001.pdf [PDF]

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