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First Crop Seed Yield of Selected Cool-Season Grasses as Influenced by Weed Control¹

Perennial grass grown for seed is an important part of the economy of Pacific Northwest agriculture, both as a crop and as an integral part of the rotation practices for control of soil erosion. Annual weeds are often difficult to control and extremely damaging to grass seedlings in the year of stand establishment. A 3-year field study was conducted on a Palouse soil (fine-silty, mixed, mesic pachic Ultic Haploxerolls) to determine the influence of control of witchgrass (Panicum capillare L.) and annual broadleaf weeds in the year of establishment on first seed crop yield of ‘Sherman’ big bluegrass (Poa ampla Merv.), ‘Whitmar’ bluebunch wheatgrass [Agropyron inerme (Scribn. and Smith) Rydb.], ‘Durar’ hard fescue [Festuca ovina var. duriuscula (L.) Koch.], ‘Pennlawn’ red fescue (Festuca rubra L.), and ‘Manchar’ smooth brome (Bromus inermis Leyss.). Bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) was applied to these grasses at 0.56, 1.12, or 1.68 kg/ha at the single leaf stage and MSMA (monosodium methanearsonate) was applied at 3.36, 4.48, 5.60, or 6.72 kg/ha when perennial grasses had five tillers and witchgrass was at the four- to eight-tiller stage of development. Bromoxynil applied at 0.56 kg/ha controlled annual broadleaf weeds and, except for red fescue, there was no effect from increased bromoxynil rates on first crop seed yields. Pennlawn red fescue yield was increased with 1.68 kg/ha bromoxynil. Applications of MSMA generally increased grass seed yields because witchgrass was controlled. Except for smooth brome, control of witchgrass and annual broadleaf weeds aided grass seedling establishment and increased first crop seed yield. Apparently, the larger-seeded grasses such as smooth brome have the ability to establish rapidly and to effectively compete with annual weeds.

Key Words: Bromoxynil • MSMA • Panicum capillare L. • Annual weeds

² Research agronomist and research agronomist (retired), USDA,ARS, Washington State Univ., Pullman, WA 99164.

Received for publication November 13, 1981.