Relieving Pressure with Residuals
Spring is upon us here in Southern Alberta. My first crocus flowers are out and the daffodils, hyacinths, and tulips are poking through. Sure, they get a little snow on them, and some freezing temperatures, but the trend is in the right direction.
You know what else is up? The weeds. Yup, they are showing up very well in my other flower beds and my new strawberry patch.
Shifting to the field, my article this month is all about strategies for making chemcial controls work better. We will need new techniques for weed control as herbicide resistance continues to chip away at our tools, but for right now, we need to use what we have.
Residuals, in-crop chemistry, crop competition, and rotation all interact to have a greater effect than what is used in any single season. Read on to learn more, and see an excellent example of how an unintentional check strip that showed the power of residuals.
In case you’re new here, let me introduce myself. My name is Scott Gillespie and I’m an Alberta-based author, podcaster, and independent agronomy consultant.
I have nearly two decades of experience in dryland and irrigated specialty crop systems, working across organic, conventional, and regenerative farms. Through my consulting, my podcast (Plants Dig Soil), and my book (Practical Regeneration: Realistic Strategies for Climate-Smart Agriculture) the basis of my advice is simple:
Science-backed practices that promote environmental stewardship and farm profitability.
Same content. Different Ways to consume.
Relieving Pressure with Residuals
Today I want to talk about weed control — but not in the usual sense of products or timing charts. More in terms of how the system actually behaves over time.
This came out of something I saw last year in a pea field. It wasn’t planned. It was one of those unintentional check strips that show up when something doesn’t quite go right. In this case, and like most unintentional check strips, it probably showed more than anything I could have set up on purpose.
The crop was yellow peas, and we had applied a granular pre-emerge product ahead of planting. The chemistry was a mixture of Group 3 and Group 8 — older chemistry, but still useful. Wild oats were the main concern, but lambsquarters and kochia had been creeping in over the years as well.
Early in the season, everything looked pretty clean. I had been digging in areas that used to be thick with wild oats and wasn’t finding much. It looked like things were working. Then along the edge of the field, I noticed a strip that stood out. It didn’t take long to realize it was a check strip — a pass that hadn’t received the pre-emerge chemical.
Because of how the irrigation pivot was set up, a portion of the pivot missed the chemical application, but was still seeded with peas. So what we ended up with was a very clean comparison: One side with the residual, one side without.
The difference was pretty obvious. Where the residual had been applied, early wild oat pressure was zero. Where it hadn’t, they came up thick. It happened that the check strip was through one of the bad patches in the field.
The takeaway for me wasn’t just that the residual “worked.” It was how much pressure it took off everything else. We still went in with an in-crop herbicide, and in that field it did its job. That tells me resistance hasn’t shown up there yet — at least not in a major way.
But that’s not always the case. I’ve seen other fields where similar chemistry doesn’t hold anymore. That’s where I think residuals are often misunderstood. They’re not a replacement for in-crop herbicides. They’re not a one-pass solution.
What they do is reduce early pressure so that the rest of the system has a chance to work. Some residuals stop weeds before they ever emerge. Others let them come up but weaken them — smaller roots, slower growth, and less competitive.
There’s also the seedbank side of this. When a residual causes a seed to germinate and fail, that seed is gone. It’s not coming back. But it doesn’t mean the seedbank is gone. You’re only affecting the seeds that try to germinate while that chemistry is active. The rest are still there, waiting for their opportunity.
A residual handles the first flush. An in-crop application handles what escapes.
Crop competition holds them back in season. Crop rotation helps to hold them back year over year.
I talked about rotation last month. It doesn’t fix problems overnight. It just slowly changes the environment so weeds — and other pests — don’t get comfortable.
Different crops shift timing. Different canopies change competition. Different herbicide windows change exposure.
Winter wheat is a good example of that. In some years, it gets ahead of wild oats enough that you can skip a grass herbicide. Not always, but it happens.
The weeds are still there. But they’re not winning in the same way.
For the full article go to:
https://www.betterfarming.com/flippingbook/better-farming-prairie/2026/march/46/index.html
Closing remarks
Thanks for your attention! If something resonated let me know. I love to hear from people. Also, sharing this episode in your social networks, whether a post or to small group of your friends, colleagues, or clients, is very much appreciated. You can also support me by picking up a copy of my book, Practical Regeneration, or reaching out for agronomy support.
All the information can be found on my website:
www.plantsdigsoil.com
Here’s to growing more, believing less, and always digging a little deeper.
