​This editorial was produced by Glacier FarmMedia’s sponsored content team on behalf of DuPont. The Western Producer’s editorial department had no involvement in the creation of the content.

How to stop weeds from getting a head start

After a wet harvest, your pre-seed burn-off is more important than ever.

It’s never too early to start planning for spring seeding, and that’s especially true this year after the wet harvest across most of the Prairies. Wet soils will mean more problems getting the crop in, and some additional weed control challenges afterward.

One will be volunteer canola.

“The length of time many canola crops were either left standing or laying in swaths, more than likely increased the amount of canola shelling out, perhaps resulting in a higher-than-normal level of volunteer canola,” says Sonia Matichuk, a technical sales agronomist with DuPont in Vermilion, Alberta. She says it’s important to control volunteer canola early, as it can germinate quickly and choke out pulses or cereals.With 20 million acres of canola seeded across the Prairies last year, that could be a significant problem this season.

The wet fall may also have prevented any control of winter annuals or biennials, so there will also be many acres of those ready for a quick start this spring.
DuPont technical sales agronomist Doug Fehr says cleavers will be among them.

“Growers really need to be aware of issues with cleavers. It is a weed that we usually have seen as a spring weed however we are starting to see it as a winter annual.”
Fehr says early control will be important because some herbicides are proving less affective when cleavers are larger.

“This may mean that growers need to bump up their glyphosate rates as well as adding another mode of action (MOA). For example they may need to increase from 180 grams active (ingredient) per acre to 240 or 360 active grams per acre.”

Pre-Seed Burn-Off

Matichuk says the pre-seed burn-off is a key operation for growers every year.

“However, I see it as even more important this year because with the relatively warm fall, combined with the moisture, germination and development of many winter annuals has been spurred. Of special concern are narrow- leaved hawk’s-beard, dandelion, cleavers, stinkweed, shepherd’s-purse, and in central and northeastern Alberta, also white cockle and scentless chamomile.”

If not controlled early, winter annuals will rob the soil of valuable nutrients and moisture. Doing a pre-seed burn-off and getting rid of the weeds when they are most vulnerable to treatment will allow for better crop establishment, leaving more valuable nutrients and resources for the crop.

“If you don’t do a pre-seed burn-off, those weeds will start to accelerate in their growth, and then you have to deal with bigger weeds in an earlier crop stage. You may just finish seeding and get pushed into an earlier in-crop spray to control those weeds that have gotten a foothold,” says Fehr.

“The grower needs to understand they have really only two windows to achieve weed control in the current season’s crop (assuming it is not Roundup Ready): pre-seed or in-crop.”

Growers need to consider options if they don’t get control of certain weeds in specific crops. For some crops, and for some weeds, there will still be some options in- crop.

“But if you don’t get control of narrow-leaved hawk’s- beard in your peas before seeding for example, you’re hooped,” Fehr says. “You have no choices for peas, chickpeas or lentils in-crop.”

Know Your Enemy

Scouting is an important first step — you need to know what weed species are present, and their stage.

Growers should ask themselves several questions. What have been their past weed problems? Which are the winter annuals which will be coming up early? What is the planned crop for that field? If it is a cereal, there are a number of options to add to glyphosate. If it is a pulse crop, the options are a lot more limited.

Matichuk says early scouting is important, because once the crop is in, you need to look for different options. “I would suggest getting out of your truck. You will not get enough detail with a drive-by. Move the trash and see what’s starting to grow under the trash. I have talked to growers who thought the field looked clean, skipped the pre-seed burn-off and then shortly after seeding they were battling well-established weeds.”

Best Practices

Glyphosate is generally used as a base for all pre-seed burn-offs and over the last 20 years or so additional products have been added — typically a broadleaf compound. Initially this was to increase performance or the number of weeds controlled, but is now also about reducing the risk of resistance.

The second product should have a different mode of action. It will give sharper control on some of the tougher weeds such as dandelion and narrow-leaved hawk’s- beard than even an increased rate of glyphosate alone, and reduce resistance risk.

“In some areas the grower may need to go to three modes of action if you are dealing with some resistant kochia. This is more of an issue in southern Alberta and Saskatchewan,” says Fehr.

Extended weed control is a good option for cereals and offers effective control of volunteer canola and better control of cleavers. When both compounds are systemic, they offer better control of some of the more established perennials or biennials.

“It is difficult to get control of the entire weed with a contact-only product,” Fehr says. “When you have two tank-mix partners like glyphosate and another systemic product, they tend to provide more thorough control of those established weeds.”

He says some products now provide extended weed control for up to 15 days after application, giving improved flexibility in timing and helping to reduce pressure from heavier weed populations such as volunteer canola or flushing weeds such as chickweed, shepherd’s purse or stinkweed.

Fehr adds a note of caution for dealing with a crop that may be stressed, such as barley in wet conditions or with poor soil fertility.

“They want to be more cautious with products that provide extended control. If the crop is under stress, it is less likely to be able to metabolize the herbicide quickly. It is similar to someone with a compromised immune system being more susceptible to the flu.”

Matichuk says that while a pre-seed burn-off can typically be done about 24 hours before seeding, with some winter annuals such as dandelion and narrow-leaved hawk’s-beard, the more time you can give it, the better.

“A couple of days is better. It’s best to give it time to get through the plant and to the root.”

Think Ahead

Fehr says growers should remember that their tank- mix decisions don’t just affect weed control this year. They need to think to the future.

“In glyphosate, we have an extremely valuable tool — we need to maintain that in the marketplace because it is unlikely we will have something else as effective. So we need to use it selectively — and always tank-mix when possible.

“When we have surveyed growers we hear that about 50 per cent of them are tank-mixing for the pre-seed burn-off. We have got to get that to 100 per cent. Whether it is pre-seed or post-harvest, or chem-fallow, my message is that glyphosate should never be used alone so that we can prolong the effectiveness of this important product.”