Downy brome (Bromus tectorum) management should primarily revolve around cultural practices such as crop rotation and effective downy brome management in fallow and pre-plant management. In this context, herbicides should be viewed as additional tools rather than the answer for downy brome management. Cost, rotation restrictions and potential for resistance with the new herbicides are why growers should rely on cultural practices first for downy brome management.
Pre-plant control is an effective strategy for managing downy brome. Traditionally growers have used a stale seed bed technique, whereby fall planting is delayed to allow early flushes of downy brome to emerge and be destroyed prior to seeding winter wheat. First, prepare the seed bed two weeks prior to planting. Delay seeding winter wheat until fall precipitation as soil water stimulates downy brome emergence. Destroy the initial flush with tillage or herbicide just prior to seeding. Roundup (glyphosate) has been the most popular herbicide for pre-plant management of downy brome. Herbicide can be applied after seeding, but must be sprayed prior to crop emergence. Do not spray post-plant glyphosate unless certain that the coleoptile of wheat has not begun its growth and emerged through the surface. Roundup should be applied with ammonium sulfate. Be sure to follow the label for proper application methods and rates.
Over the past several decades, crop rotation has been the principal management strategy for control of downy brome. Only seeding winter wheat once every 3 or 4 years can successfully control downy brome populations. For example, downy brome populations increased from 2 to 60 plants per ft2 after 3 years of continuous winter wheat in research trials. In contrast, winter wheat - fallow or winter wheat - canola rotations maintained downy brome populations below 10 plants ft2 in the same study. As a result, a number of Montana growers have adopted a 3 or 4-year rotation that alternates spring seeded crops and fallow with winter wheat. Select fields for seeding winter wheat where the downy brome has been effectively cleaned up by crop rotation.
Managing downy brome in fallow is another important control practice. In traditional tillage systems, the continual disturbance of the soil during fallow stimulated downy brome seed to germinate. Now that many producers have gone to conservation or no-till operations, the soil is disturbed less. As a result, the downy brome seed sits on the soil surface and is less likely to imbibe water and germinate. The lack of germination allows for increased persistence of the seed in the soil. Downy brome seed persisted only 1 to 2 years in the soil under traditional fallow , but now remains viable for 3 to 4 years in conservation or no-till systems. Fortunately, producers in Montana have successfully adopted 3 or 4-year rotations (primarily for disease management) that include spring annual crops. Success of spring crops varies throughout Montana.
Maverick is labeled for control of downy brome in winter wheat. The recommended label rate of Maverick is 2/3 oz/A with a minimum of 5 gallons of water. Maverick works best when applied post-emergence in the fall. Spring Maverick applications generally reduce downy brome activity 20 to 30%. Maverick has long residual activity in the soil and injures barley. Barley should not be seeded within 22 months of a Maverick application and a field bioassay should be done. This is especially true when the conditions are dry or soil pH is high.
Maverick has the most potential in MT as a rescue treatment for downy brome, in the event that other control practices fail.
Soil applications of Finesse or Amber prior to crop emergence have successfully managed downy brome in some producer fields. Finesse and Amber are often applied in combination with Fargo. MSU research suggests control of downy brome with these products varies between 20 to 80%. Soil applied Amber and Finesse can also be extremely injurious to crops – especially if the herbicide is incorporated (through precipitation or tillage) to the seed and root zone of wheat in the soil. Apply 2,4-D post-emergence to safen wheat from Finesse or Amber injury.
Finesse, Amber and Fargo are only recommended for downy brome control if the producer is satisfied with past experiences and knows the potential risk of crop injury and lack of control.
Sencor is another product available for control of downy brome. Although labeled for winter wheat, fall applied Sencor can cause severe crop injury and reduce stands up to 80%.
Categories: Weed, Downy Brome, Integrated Weed Management
Date: 04/15/2005