SOIL-TEMPERATURE AND MOISTURE EFFECTS ON DOWNY BROME VS WINTER CANOLA, WHEAT, AND RYE EMERGENCE

Downy brome (Bromus tectorum L.) causes serious yield reductions in winter cereals in the western USA and Canada. Current control practices often are ineffective. A study was conducted under controlled-environment and field conditions to determine the effect of soil temperature (5-30-degrees-C) and moisture (-0.03 to -1.53 MPa) on the rate and total emergence of downy brome relative to that of winter cultivars of canola (Brassica napus L.) wheat (Triticum aestivum L.), and rye (Secale cereale L.) with the aim of developing improved cultural control measures. A strong temperature-moisture interaction was found for all species. Downy brome emergence was affected more by varying soil temperature and moisture conditions than rye or wheat but less than winter canola. Wheat and rye emergence was > 88 and 82%, respectively, across the entire range of soil temperature and moisture conditions. Canola emergence decreased to < 60% in cool, dry soils. Downy brome emergence remained > 70% for all soil temperature and moisture conditions, a sufficiently high percentage to pose a serious weed problem. Downy brome usually emerged more slowly than the crop species, but the additional time required to reach 50% emergence compared with that of the crop species was no more than 8 d. Results indicated that differences between downy brome and canola, wheat, and rye in their soil temperature and moisture requirements for optimal emergence are likely insufficient to allow development of cultural control practices to reduce the establishment of competitive stands of downy brome in these winter crops.