Manage early weeds for season-long benefits

Early control allows canola crops to germinate with unfettered ccess to moisture, sunlight and nutrients

 

It won’t be long until it’s time to seed canola. But when the frost comes out of the ground and early weeds are already coming to life, farmers should consider what to look for in a pre-season burnoff for early weed control.

“At the beginning of the season, a pre-season herbicide application is meant to clean up the field in order to give the crop the ability to get established,” says Sonia Matichuk, Technical Sales Manager with FMC. “Canola growers need to clean up winter annuals like flixweed, stinkweed, cleavers and earlygerminating annuals like kochia, lamb’s quarters and more. They also need to make sure they are taking care of weeds which can continue to grow after the crop has been seeded.”

Early weed control in canola allows the crop to germinate with unfettered access to moisture, sunlight and nutrients. The early critical weed-free period has long been defined as the portion of the life cycle of the crop that must be kept weed free to prevent yield loss. As the crop progresses and becomes well established, growers can then deal with the next flush of weeds which are generally smaller, allowing them to get more efficient, better use from an in-crop herbicide application.

“There have been several historical studies completed on the early competitiveness of canola and weeds, and they have shown it makes all the difference in the early success of the crop when early weeds are controlled,” says Nolan Kowalchuk, Technical Sales Manager with FMC. “We really see the difference in dry years when the weeds are grabbing all the moisture required by the crop to get established. When you control the weeds before the crop is established, this not only allows that early-germinating canola crop to grab the early moisture, but when you eventually do get later moisture, it is available to the canola, not the weeds.”

In general, growers want to control those early flushes of weeds for a weed-free seedbed, but they should have other considerations in mind as they plan their burn-down options. What tank mix will be the most effective resistance management tool? Which will have the longest extended control to get them through the critical weed-free period? What are the additional benefits of early weed control?

New for 2020, Command®Charge from FMC is a pre-seed canola herbicide for burnoff management of broadleaf weeds. Command Charge contains the unique Group 13 chemistry clomazone and the Group 14 carfentrazone actives. It is tank-mixed with Group 9 glyphosate for broad-spectrum weed management of emerged weeds and up to four weeks of extended cleaver control.

MANAGING A CHALLENGING WEED

Cleavers have become an increasing management concern for canola growers. If growers don’t get control of this weed during their burndown, it often gets too big to be tackled by an incrop herbicide. By the time it’s applied, they have grown past the stage where the herbicide is the most effective. A University of Manitoba study showed that cleavers densities of 100 plants per square metre can result in a 20 per cent yield reduction in canola.

Cleavers can become tangled in the growing canola plant, leading to harvest problems. Cleaver seeds are about the same size as canola seeds, so if enough make it to harvest, they can increase dockage and lower grades. Number one canola must have fewer than one per cent of other seeds that are not readily separable, with the limit at 1.5 per cent for number two grade and two per cent for number three.

A study by the University of Saskatchewan foundthat an application of clomazone — one of two active ingredients in command charge — prior to seeding canola, followed by an in-crop herbicide application provided greater than 85-90 per cent cleavers control.

“Herbicide-tolerant systems have some great advantages for growers,” says Kowalchuk. “But if they have one weakness, it’s cleavers. The ‘Command’ aspect of Command Charge, as a Group 13, offers the extended control of emerging cleavers, working with the carfentrazone and glyphosate as Groups 14 and 9 to take on the weeds that have already emerged. Depending on your soil type, that extended control action can last from two to four weeks. The ‘Charge’ aspect tackles a wide variety of broadleaves including lamb’s quarters, roundleaved mallow, kochia and more. That is a lot of protection for an early-emerging canola plant.”

There is a lot of ongoing discussion about glyphosate resistance as glyphosate-resistant kochia is a real issue and reports of resistant wild oats emerge from Australia. Rotating in a different mode of action is a stewardship message that makes sense.

“Growing canola is the only time a Group 13 mode of action can be used on any crop to control cleavers, and there is no known resistance to this group,” says Matichuk. “You want to extend the livelihood of glyphosate as it provides control of a variety of early weeds in canola. You can’t rely on one product for pre-season burn-down, so this provides more options in your tool box. When you add in additional modes of action you are able to control more weeds without the reliance on one chemistry applied repeatedly, risking selection for that chemistry.”

The objective is a high-yielding crop with a positive return on investment at the end of the season. Agriculture and Agri-Food Canada scientists Neil Harker and John O’Donovan have estimated that the yield loss from a single weed emerging a week before the crop is equal to 100 weeds emerging three weeks after the crop. Eliminating weeds before the four-leaf stage of the canola crop’s development is important. After that point, few weeds emerge and even those that do have little to no effect on yield.

“Keeping your field as weed free as possible opens up the opportunity to the best yield possible,” says Kowalchuk. “If you have only small weeds inseason, they are easy to manage with your in-crop herbicide, allowing your crop to take off. You will still have to do an in-crop weed control application, but your pre-seed burn-down will have done a lot of the heavy lifting early on, and with Command Charge you will have the benefit of some extended control as well.”

 

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