Soybean School: Warm winter creates spring weed challenges

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An open fall, warm winter temperatures, and a mild spring that has now turned cool and wet all add up to big weed control challenges as the calendar gets ready to turn to May.

From cover crops that refused to die under snow cover, to hardy oats, tough annuals and an abundance of volunteer wheat, growers have their hands full this spring, says BASF agronomist and technical development manager Rob Miller.

On this episode of the RealAgriculture Soybean School, Miller says a species like chickweed is a good indicator of the health and vigour of weeds in the field. “If the chickweed is flowering, that means a lot of the other winter annuals and perennials are still growing,” he notes. “They’re not necessarily growing vegetatively, but they’re definitely putting down some larger roots… We’re seeing some pretty large dandelions. They don’t look that big from the top of the soil surface, but they’re starting to get a really large, thick root on them. And that’s going to be difficult to control.”

Other weeds are also hitting growers’ radar screens. Miller has been fielding questions about both annual bluegrass and rough stock bluegrass. They’re tough to handle because glyphosate it not really effective, and the species tends to grow in clumps which also renders tillage ineffective as it turns the seedbed into a mass of lumps. “It germinates in the fall, as well as in the spring. It tends to be more of an issue on some of those heavier clays, but we’re starting to see it move in across provinces to other areas as well.”

Miller is advising growers to get out and scout. He says lingering cover crops and oats are pretty sensitive to glyphosate, but it’s important to choose the right rates based on what’s in the field. He notes that glyphosate tends to work slowly in cool spring conditions and a rate that controls volunteer wheat may not be enough to take out larger perennial weeds.

“Select the rate that’s required based on the field and then add in that second additional mode of action. That’s very important,” says Miller. He recommends spraying prior to fleabane bolting and dandelion flowering โ€” it’s important to get those weeds before they get too big.

Applying weed control early is beneficial, but patience is also rewarded, says Miller. When it comes to glyphosate, it’s “actually better to spray it on more of a warming trend. You get much faster, more consistent weed control instead of trying to apply some of these products in this type of [cool] weather.” (Story continues after the video)

Miller also addresses growing concerns about Group 14 resistant common ragweed โ€” a great concern for growers who plant identity preserved soybeans. “We also have populations that are resistant to glyphosate, Group 2, as well as the triazines (Group 5)”, he adds. A key strategy is to control these weeds in other crops where more herbicide options are available.

“Have a really good solid foundation in your corn crop, making sure that you control some of those ragweed seeds after the wheat has been harvested,” says Miller. It’s important to prevent the ragweed from going to seed. He also recommends growers use a herbicide layering approach, which includes early and aggressive scouting, having residual down at planting, controlling the weed before it gets too big and having residual down in-crop to provide control later in the season.

The interview wraps up with a pitch for growing good crops. It’s a great form of weed control, says Miller. That includes getting the crop off to a great start and making good agronomic decisions that promotes early growth, even emergence, vigorous crops and a fast-closing canopy that quickly shades out weeds. It all adds up to higher yields and better weed control.

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Soybean School (view all)Season 12 (2023) Episode 23
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