Plenty of things are showing signs of life right about now in Ontario, including the weeds. To determine how to control these yield-robbing plants in the weeks ahead, Bernard Tobin is joined by Rob Miller, agronomist at BASF, in this episode of the Corn School.

Typically, a conversation on spring weed control is determined by what happened the previous fall, and the fall of 2020 saw a lot of fall tillage.

“When we do that fall tillage, we actually rely more on post-emergence herbicides in-crop, depending on your cropping system,” says Rob Miller, agronomist at BASF. “Typically, in a no-till or minimum tillage situation we always like to apply those herbicides before you conduct that tillage, just because it is that second, additional mode of action on controlling some these winter annual and perennial weeds.”

If tillage is done in the fall it results in a rougher seedbed, so the sprayer can’t get across the field because it’s too rough. Until that roughness gets leveled out in the spring, those weeds are getting larger and they get a better chance to establish, says Miller.

Perennials that have already broken dormancy will have a chance to establish a larger root system, and it’ll be tougher to take them out with herbicides in the spring, in crop, or with tillage.

There are different forms and levels of tillage. Aggressive tillage done in the fall, followed by a cultivator with sweeps will uproot the weeds and leave them on top of the soil surface. Vertical tillers, which are a better tool for seedbed preparation, can actually exacerbate weeds and make them grow back, though perhaps with a kinked root.

In the video, Miller uses the example of Canada fleabane in a dry bean field that was unsuccessfully controlled. Story continues below video.

Usually in a tillage system, more annual weeds will come up first, and those seeds will get moved around a bit. This is when a soil-applied residual herbicide, whether pre-emergence or as part of an early emergence program, becomes really important.

“We’re only one warm rain away from everything flushing at once, whether it’s the crop or various weeds, they’re all going to flush at the same time and if you don’t have that soil-applied residual herbicide it’s going to be tough to get across all those fields,” says Miller.

If you’re a strip-tiller, one of the things learned over the years is that there’s better control of weeds in the berm if a pre-emergent herbicide is applied, after the planter has gone through, says Miller.

Lastly, it’s important to remember that tilling is only a effective at controlling some weeds, and is a stronger option when used in conjunction with a herbicide strategy.

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