Weed invasion in new stands of alfalfa seeded with perennial forage grasses and an oat companion crop

Weed invasion in alfalfa (Medicago sativa L.) may be reduced by seeding wit h a perennial forage grass, Our objectives were to determine if any of four perennial forage grasses influenced weed invasion when seeded with alfalfa , with and without an oat companion, and if this reduction was consistent a mong harvests and throughout the duration of the stand. Alfalfa was seeded alone and in binary mixtures with smooth bromegrass (Bromus inermis Leysser ), orchardgrass (Dactylis glomerata L.), timothy (Phleum pratense L.), or K entucky bluegrass (Poapratensis L.). All forages were seeded with and witho ut an oat (Avena sativa L.) companion crop in May of 1993 and 1994. Seeding grasses with alfalfa occasionally reduced meed yield in the first 2 yr Of the stand. Weed density was not influenced by the perennial grasses in the seeding year, In the third year, mixtures containing orchardgrass or Kentuc ky bluegrass reduced weed yields by 20 to 130 kg ha(-1) in three of four ha rvests and dandelion (Taraxacum officinale Wigg.) density up to 5.4 plants m(2) (71%). Bromegrass and timothy did not persist with four annual harvest s. Seeding the mixtures with an oat companion reduced weed and perennial gr ass yield in the seeding year and perennial grass yield the following year, As a result, dandelion density in the third year was 2.6 plants m(2) (70%) greater in mixtures established with oat than without oat, Including peren nial forage grasses can be effective at reducing weed invasion by the third year of the stand if grass is maintained as a major component of the forag e.