Roadsides prone to scotch broom and alder invasion were used to evaluate the timing and rate of IBDU, Escote 150 slow release nitrogen (SRN) application and the effects of fall grass/legume overseeding on improving cover. Fall fertilization with SRN increased cover and biomass of grass along roadsides where good bentgrass or fescue populations existed. A 20 to 40% increase in grass cover was realized with fall fertilization at > 90 kg SRN ha[superscript]-1 and significantly reduced open space where seeds of invading species could germinate. Poor grass growth occurred following spring SRN application and 45 kg N ha[superscript]-1 in the fall as SRN or 16-16-16 was too low to improve cover. Liming and overseeding of grass/legume mixes were not reliable as a one-time method to improve grass/legume cover when precipitation began by early October. Overseeding may be successful if practiced regularly and by mid-September when moisture might be available during some years. No overseeding grass or legume species survived better than another when overseeded in early October. A 5-year test program is recommended. Fall apply SRN to roadsides prone to scotch broom invasion where good bentgrass/fine fescue populations exist. The SRN should consist of a 0.6 cm minus particle IBDU, Escote 150 and urea combination (40:40:20 w/w, respectively) in a 2:1:1 ratio with P2O5 and K20 in a 2-1-1 ratio. Divide each test area into annually mowed, biannually mowed or non-mowed areas. Overseeding with fertilization should occur in early September. The seed mix should consist of 70% improved varieties of slender, creeping red or hard fescue, 20% fine-leaved perennial ryegrass and 10% colonial bentgrass. Dwarf white clover, although a desirable component of the mix, is not suggested unless seed is pre-inoculated and sufficient P, K and lime have been previously applied.
Washington State Transportation Center (TRAC)
Grasses, Ground cover, Fertilizers, Invasive species, Landscape maintenance, Nitrogen, Plants, Roadside, Roadside flora, Trees, Vegetation control.