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March 2,
2006 - FOR IMMEDIATE RELEASE
Dandelion is a well-known weed pest in lawns,
pastures and forage crops, but is generally not considered a serious
concern in annual crops. However, results of weed surveys in
Manitoba show that dandelion is becoming more and more troublesome
in fields where annual spring crops are grown. In the five
years between 1997 and 2002, dandelion went from Manitoba’s 22nd
most abundant weed in annual cereal and oilseed crops to 9th
most abundant.
“Driving across Manitoba in the spring, it’s
not difficult to find significant infestations of dandelion in field
crops,” says Dr. Rene Van Acker, plant scientist at the University
of Manitoba. “But, it’s only in recent years weed scientists
have been looking beyond perennial forage crops and turf grass and
asking why dandelion has become such a prominent weed pest in field
crops.”
In 1999, Van Acker applied for a grant from the
Canada-Manitoba Agri-Food Research and Development Initiative (ARDI)
to study dandelion control in canola. Graduate students Nathan
Froese and Kristin Hacault conducted their field research over two
years at sites near Carman and Oakville. One of the research
team’s most significant findings is that true dandelion seedlings do
not appear until early summer (mid- to late-June), meaning that weed
control efforts in the spring are not attacking new growth.
Traditional spring weed control targets only the plant material that
has over-wintered and is regenerating from established rootstock.
The study results show the best time to apply
herbicide for dandelion control is in the fall, for two reasons:
first, herbicide applications applied in the fall will kill the
seedlings as well as the rootstock; and second, dandelions are much
more vulnerable to herbicide applications in the fall. In the
case of dandelions, timing really is everything. Van Acker
found that a single post-harvest application of one litre Roundup
per acre reduced dandelion density and plant size by 88 and 96 per
cent, respectively, the following spring. Pre-plant or in-crop
applications were not nearly as effective.
Field studies also examined the effects of
spring tillage. The results showed that spring tillage in
non-treated control plots led to reduced shoot dry matter the
following year, but did not reduce overall dandelion density.
So, while spring tillage may not kill established dandelion plants,
it does injure them substantially. Van Acker has since
verified these results in spring wheat field trials.
“The main message to producers is that fall
herbicide applications provide the best control of dandelions,” says
Van Acker. “Dandelion infestation is dependent upon seed
movement and seed establishment, so in order to halt the spread of
this weed, weed control must happen after the seedlings emerge.”
ARDI is a research and development granting
program of Agriculture and Agri-Food Canada and Manitoba
Agriculture, Food and Rural Initiatives. It is funded through
the Agricultural Policy Framework, a federal-provincial-territorial
long-term action plan for agriculture. The full research
report, Dandelion Biology and Control in Conventional and
Zero-tillage Roundup Ready Canola, can be found at www.gov.mb.ca/agriculture/research/ardi
under Oilseed Crops.
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