Agenda - Parks and Recreation Commission - 06/09/2005 - Joint with CC

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Willow Control I,:~ [Lqmsey, Sandbar willow is very prevalent due to more than 15 % of the city being comprised of wetlands, where there are the most favorable soils for their growth. These same areas are largely unbuildable, and have margins adjacent to residential uses, xvhich encourages the siting of trails adjacent to this same ~ ~penspace. Willows only naturally occur in alluvial soils or along streams, but will thrive in areas where this same soil is imported as fill material for 'shouldering' trails. Care must be taken when using this fill that it ~_hms not contain any root stock or seed material from locations where the willows were growing. Mechanical and Chemical Control of Willows '[lhere are several instances where a willow control or eradication program should be used. The most prevalent is along trails that are in e.,dstence with willows in direct proximity. Another is where willow may be in the vicinity of a trail and can be expected to expand towards the trail surface. Yet another is in situations where a trail is planned, but not yet constructed. The folloxving are specific measures to be taken for the control of willoxvs: Willoxvs are already a problem In areas ~vhere xvilloxvs are already impacting the bituminous surface the first step is aggressive mowing of dte shrubs as close to the ground as possible. From the edge of path, a minimum distance of 10 feet ~;hould be considered. The usual equipment for this task is a 'bush-hog' behind a tractor with a three-point attachment. Tile most successful approach is to mow the willow after the f'mst flush of spring gro,arth - then allow a couple of xveeks for revegetation. This provides the most stress upon a very hardy plant. When the shrub is lea£mg significantly and extending its growth vertically, herbicide should be applied. The above fining will occur in about late May, xvhich is also when optimal temperatures can be expected to be present (at or below 70 degrees F). Diligent follow up is required, and repeat applications of glycol phosphate can be expected. In some instances, 2-4,d may be preferred so as to preserve turf grass that may be groxving xvith the willoxvs. After tile mechanical disturbance of the tops of the willows, a curtain or barrier of two or more feet in depth should be inserted immediately alongside the bituminous surface vertically. A 1997 study by the Darer Resource Group showed that two materials were effective in arresting the regrowth of tree roots in to trenched areas, black plastic (9mil)and Biobarrier brand root control system. While both methods were effective, the authors recommended Biobarrier as root growth was terminated V4 inch from the material. Wherein, with the black plastic, roots grew up to, and along the plastic, suggesting that roots were likely to eventually 'find' a xvay through. '1 'he above addresses all of the willoxv growth outside of the trail surface. Roots, if already under the path, can be expected to continue to groxv. If the willows are exposed within the trail surface, herbicide or judicious use of soil sterilant may be in order. The other alternative is the complete reconstruction of the ~rail (refer to 'proposed trail', below).