Submitted to: Pendleton Station Field Day
Publication Type: Experiment Station
Publication Acceptance Date: 4/12/1995
Publication Date: N/A
Interpretive Summary: Incidence of downy brome (a grass weed) in winter wheat fields in the Columbia Plateau has been observed to be greater in fields where crop residue was left on and near the soil surface for soil conservation than in fields where the residue was buried with tillage. A field experiment was conducted to determine if the increase in downy brome emergence was related to the amount of crop residue on the soil surface. Crop residue (up to 100 percent of ground cover) did not influence the amount of downy brome seedlings established. Tillage systems that leave crop residue on the surface also leave weed seeds near the surface where the seeds are more likely to germinate and establish seedlings as compared to tillage systems that deeply buried weed seeds. The probable cause for observed increased incidence of downy brome in conservation tillage systems is the placement of weed seeds and not the placement of crop residue. This finding will impact the development of conservation tillage systems and weed control in cereal crops.
Technical Abstract: Farmers in the Columbia Plateau have noticed a marked increase in the incidence of downy brome (Bromus tectorum L.) in winter wheat fields when they used conservation tillage that left sufficient crop residue on the surface to comply with conservation requirements. A field experiment was conducted to determine if the increased incidence in downy brome was due to crop residue or other factors associated with the tillage practices that leave residue on and near the soil surface. Four replicate plots were seeded with downy brome seed and covered with wheat residue varying from 0 to 100 percent cover. Downy brome emergence was observed during the fall. There was no statistically significant relationship between downy brome emergence and the amount of residue cover. It is probable that the grower observations of increased downy brome in conservation tillage systems were related to the fact that these systems leave more downy brome seeds near the soil surface where they readily emerge.