The ecological effects of roads impact nearly 15% of the land area of the United States, an area equivalent in size to all conservation areas of the country combined (Wilkinson et al., 2008). Planting roadsides with native species can displace nonnative or potentially noxious plant species (Landis et al., 2005). Weed control may be essential for the long-term survival of native species when developing reliable and efficient roadside establishment protocols. Seashore dropseed is a perennial, coastal salt marsh grass that spreads by rhizomes, forming extensive colonies, and has potential as a low-maintenance groundcover in saline areas (Marcum and Murdoch, 1992). In Hawaii, seashore dropseed is typically found in low-lying areas with an abundant source of subsurface water. The potential of seashore dropseed to establish and thrive in high-saline soils is a valuable attribute in coastal restoration (Ashour et al., 1997; Semple et al., 2006).
Seashore dropseed produces very few viable seeds requiring vegetative propagation for large-scale plantings. Vegetative propagation of seashore dropseed using terminal stem cuttings is preferred to harvesting rhizomes that severely disrupt stock bed root systems. Harvesting terminal stem cuttings also promotes vigorous growth in the stock plant and ensures a regular yield of planting material (Baldos, 2009). Improved rooting of seashore dropseed stem cuttings is obtained after a 24-h soak in a rooting hormone (Baldos, 2009).
The potential for excessive erosion from roadside areas is greatest after setting the finished grade and before establishment of permanent vegetative cover (Holt et al., 2005). The erosion hazard can be reduced by hydroseeding or hydromulching (Babcock and Mclaughlin, 2013). Hydromulch caps can be customized with various materials to suit specific vegetation needs. Hydromulch is a water-based slurry of shredded paper, fine straw, and a tackifier, designed to adhere plant material to the ground and provide a protective top layer. In Hawaii, seashore dropseed is slow to establish (>3 months) from cuttings and provide a weed-suppressing canopy. Preemergence herbicides can greatly increase the success of native plant establishment (Tjelmeland et al., 2008). Established native species resist weed invasion (Borman et al., 1991), and use resources efficiently, leaving fewer resources available for weed recruitment (Herron et al., 2001). Baldos et al. (2010) determined that excellent weed control could be obtained during field establishment with seashore dropseed plugs with the use of spray applications of oxadiazon (4.0 lb/acre) (Baldos et al., 2010). The objective of this groundcover establishment study was to evaluate the response of weeds and cut stems of seashore dropseed to two rates and two formulations of oxadiazon, incorporated into a hydromulch cap.
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