Downy
brome: What do you need to know to manage it?
Fabian
Menalled.
MSU Extension Service Cropland Weed
Specialist
2007
has been the year of downy brome (Bromus tectorum). All across
Downy
brome was first introduced into the United Sates from
At
the seedling stage, downy brome is difficult to differentiate from other brome
grasses. However, as a mature plant downy brome is easily recognized by its
flat leaf blades densely covered with soft and long hairs and by its relatively
tall and serrated ligules. As reproductive plants, downy brome reaches 4 to 30
inches tall and has 2 to 6 inches long, dense, slender and usually dropping
inflorescences. At maturity, these inflorescences have characteristics three-eighths
to five-eighths-inch long purplish awns. These awns attach to clothing or
animals, so downy brome seeds spread easily. Seeds can also be dispersed by
contaminated straw and farm machinery. Each plant can produce up to 400 seeds,
with most of those seeds remaining viable for two or three years.
Downy
brome ecological success is mostly due to its ability to use moisture from the
soil's upper layers, allowing seedling to out-compete more desirable plants
early in the growing season. Once establish, downy brome can inflict
significant economic costs, reducing crop yields, becoming crop-seed
contaminants and lowering weight gain of grazing livestock. After maturity,
downy brome is extremely flammable, greatly increasing fire hazard.
Unfortunately, burning does not effectively prevent seed set, and site
disturbances caused by fires have been associated with increased rates of downy
brome establishment and spread.
Worldwide,
downy brome has developed resistance to many herbicide families including
Photosystem II Inhibitors such as atrazine and Ureas and Amides such as
chlorotoluron. In
Developing
integrated strategies for managing downy brome is a key to successfully reduce
its spread and impact. In doing so, agricultural producers and land managers
should combine cultural, biological, mechanical and chemical practices to
achieve a three-fold goal. First, it is necessary to prevent the spread of
downy brome into new habitats and maintain its density in sites already infested
at levels low enough to minimize its harm to the ecosystem. Second, management
practices should be aimed at increasing downy brome natural mortality through
the establishment of highly competitive vegetation. Finally, it is fundamental
to keep downy brome "off balance" by maximizing moisture, nutrients
and light capture by the desired vegetation.
Increasing
our knowledge on the biology and ecology of downy brome can help us develop these
integrated management practices. For example, research conducted at several
universities suggest that conservation tillage regimes, broadcast nitrogen
fertilization, extensive use of shorter and less competitive cereal varieties,
and the lack of crop diversification lead to increaseing downy brome in
agricultural landscapes. Simple changes such as using cultivars with high
tillering ability and leaf area, banding nitrogen, increasing crop seeding rate
and developing a diversified crop rotation that includes broadleaf crops, help
control downy brome. In this context, herbicides should be regarded as just additional
tools rather than the "silver bullet" for downy brome management.
Herbicide
options to manage downy brome are limited due to its inherent tolerance to many
products. Maverick (sulfosulfuron),
Roundup
(glyphosate), Journey (imazapic plus glyphosate), or Plateau (imazapic) can be
used to help managing downy brome infestations in Conservation Reserve Programs
(CRP) land. Roundup can be applied in established CRP, but applications should
be done in early Spring to prevent weed-seed production. Also, care should be
taken to apply glyphosate only to dormant grass to avoid risk of injury of
desirable plant species. For best results, Journey should be applied on CRP
land in late summer or fall before downy brome emerges. Spring applications of
Journey can be done to increase consistency in control. However, these spring
applications should be limited to areas without a large number of desirable
plants. Finally, the selective activity of Plateau allows desirable native
grasses and forbs to re-establish after treatment while controlling several
weed species, including downy brome. For the most effective control, late
summer or fall applications of Plateau herbicide, preemergent to germination,
are highly recommended. Despite the potential of these products, our research
suggests that favorable moisture conditions and well established grassy systems
are essential to increase downy brome control in CRP lands.
Disclosure.
Common chemical and trade names are used in this publication for clarity by the
reader. Inclusion of a common chemical or trade name does not imply endorsement
of that particular product or brand of herbicide and exclusion does not imply
non-approval.
Categories:
Downy Brome, Integrated Weed Management
Date: 11/15/2007