Features Agronomy Weeds
Eliminate the competition with pre-emergence weed control

May 6, 2008

Control weeds early to eliminate the competition for
this year’s canola crop, says Arvel Lawson, crop production program manager
with the Canola Council of Canada. 

“Young
canola plants are not very competitive,” explains Lawson. “Weeds just
out-compete young canola plants for soil moisture and nutrients. The yield loss
can be high.”

Research
shows that weeds that emerge before or with the canola crop cause greater yield
loss than weeds that emerge after the crop is established – approximately the
4- to 6-leaf stage. But a pre-seed burnoff with glyphosate can allow canola to
develop with minimal weed competition, she says. 

Scouting
for weeds before applying a pre-seed burnoff is critical this season since the
cold, dry spring has limited weed emergence in many areas. If few weeds are
visible in the field and the ideal seeding date has arrived, consider using a
post-seed, pre-emergent treatment BEFORE seeded canola comes out of the ground,
says Lawson. First, make sure weeds are actually present.

Remember
glyphosate is a systemic herbicide that needs time to work for maximum control,
Lawson adds. Consider formulation and target weeds when determining the time
required between application and soil disturbance from tillage or seeding. 

”With
temperatures getting close to or dipping below zero at night, we recommend
spraying glyphosate only after temperatures have warmed the following day,” she
says. “After a hard frost, check for new growth before applying herbicide
because weeds must be actively growing to ensure herbicide uptake and maximum
kill.”

If
volunteer canola control is your target, the only option before canola is a
pre-seed application of glyphosate and carfentrazone. This will control all types
of volunteer canola if used at the proper stage. Applying even light rates of
2-4,D or MCPA to control volunteer canola or other hard to control winter
annuals is a bad idea because this is not a registered use prior to canola and
may result in herbicide injury to the crop, says Lawson.