Soybean School: Controlling weeds after a warm winter

A bed of chickweed is a sure sign that weeds are awake, actively growing and planting isn’t far off.

On this episode of RealAgriculture’s Soybean School, host Bernard Tobin heads to the field with BASF Canada agronomist Rob Miller to talk spring weed control and what growers should be looking for as they scout fields.

Miller says that chickweed is already starting to flower and that means weeds like Canada fleabane, dandelion and shepherd’s purse are waking up as well.

After a record Ontario corn crop in 2023, many soon-to-be soybean fields accros the province look like the plots at BASF’s Maryhill, Ont. research farm where heavy corn residue and record winter temperatures are a delightful combination for tough winter annual weeds already growing and lurking in decaying field trash.

Miller says growers will need to be more aggressive as they target these yield robbers. Many growers “didn’t have the opportunity to do any type of fall tillage, whether it was with the high-speed vertical disc, or even some type of chisel plow in these fields,” he notes. “That means we’re going to have to use a lot higher water volumes and use multiple modes of effective action, because coverage is going to be a challenge.” (Story continues after the video.)

Miller stresses the importance of early control of pests like sow-thistle, fleabane and dandelion, noting that there are few control options, especially in IP soybeans and dry beans, after planting begins. He also adds that growers have to manage expectations for early-applied herbicides because they do work slower in cooler April conditions.

In the video, Miller talks pre-emergent weed control strategy and how it can work in tandem with crop canopy to deliver effective control. He says that residual herbicides typically deliver four to six weeks of control and it’s important to time that application as close to planting as possible. “If you can try to time it and wait a little bit longer so that it’s not really exposed and sitting on the soil surface for two to three weeks before that crop comes up and get the canopy closure — that’s really the ideal thing” he says.

Miller says, however, that growers need to be realistic based on the spring weather and fieldwork demands. “It’s better to get that soil-applied residual herbicide down, especially when you’re dealing with some of these resistant weeds, the waterhemp, and even something like a lamb’s-quarters or ragweed. That’s better than not spraying at all.”

Miller also shares control strategies for other weeds he sees as he walks the field, including sow-thistle, Canada fleabane, bluegrass and whitlowgrass.

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