Renovation of Sparse Stands of Crested Wheatgrass

Abstract

Atrazine at 0.56 kg/ha and simazine at 1.12 kg/ha were evaluated for renovating sparse stands (0.9 to 1.5 m between plants) of resident crested wheatgrass. The study was repeated for 3 years for both weed control and seeding of crested wheatgrass. Both herbicides reduced yield and reproductive potential of downy brome and tumble mustard in the fallow year. Neither herbicide significantly damaged the vegetative or reproductive parts of resident crested wheatgrass plants. Atrazine residues in the soil in the fall of the fallow year and spring of the seeding year were below the toxic level for crested wheatgrass seedling. Simazine residues were above the toxic level. Both herbicides increased seed production of resident crested wheatgrass plants and neither adversely affected seed test weight and germination, or root and shoot growth of seedlings from seed of these plants. Weed competition during the seedling year was reduced by herbicide treatment. Density of crested wheatgrass seedlings and established plants was greatest on treated plots in 2 of 3 years. Based on low triazine residues and increased crude protein, resident crested wheatgrass on treated areas would be excellent forage during the fallow year. High levels of NO3- N, trans-aconitate, and K, but low Mg suggest that grass tetany could be a problem if lush herbage on treated areas was grazed during the spring period.