The Canola Council of Canada (CCC) is advising growers to remove weeds early.
“Weeds compete for light, nutrients, and moisture and a canola crop is most susceptible to this weed competition at the seeding stage,” says Arvel Lawson, CCC program manager for crop production.
Lawson points to a recent Agriculture and Agri-Food Canada study that concluded that weeds should be removed before the 3- to 5-leaf crop stage. In this particular study, delaying weed control until the 6- to 7-leaf stage reduced canola yields by 20%.
In recent years, the one pass in-crop herbicide option has become very common in canola since the second in-crop application is rarely economical. If spraying once, the ideal timing is typically the 2- to 4-leaf crop stage. The goal is to spray early emerging weeds before they start to cut into crop yield, but to delay long enough that the crop is approaching the rosette stage when it is more competitive and can keep ahead of later emerging weeds.
However, since cool conditions severely limited early season weed growth this spring, relatively few acres received a pre-seed burnoff, says Lawson. “This has created a scenario where a significant number of weeds are emerging just before or with the canola crop. This can have a considerable negative impact on yield, especially in areas experiencing a moisture deficit. With some additional heat and moisture, this competition will ramp up even more.”
When the option is available, growers may need to consider utilizing two in-crop herbicide passes this year.
“If growers are facing a carpet of weed seedlings and a canola crop that is just poking through or is at the cotyledon or seedling stage, an early herbicide application within label guidelines may be necessary”, says Lawson. “Then before applying the second in-crop, growers should scout to assess weed densities and crop competitiveness. That’s the way to determine whether the second application is truly economical.
“Protecting a canola crop from weed competition early in the season is critical. Though holding off on spraying to hit more weeds in the first application can be an appealing option, it is also a risky one, especially if weed densities are high. Later-emerging weeds may be unattractive and they contribute to the seed bank, but they have much less impact on yield than do weeds that compete early in the season.”
For more information, contact:
Program Manager for Crop Production
Canola Council of Canada