High-Tech Weed Control: Fighting Herbicide Resistance Without Reversing No-Till Gains

Wednesday, June 18, 2025

By Scott Gillespie

I grew up on my family farm in the 1980s and 1990s. Before the switch to no-till, I can remember a couple of tillage passes to supplement weed control. This was before herbicide-tolerant crops. The chemical controls were good at what they did, but they needed a little help.

Rotary harrowing was used to get the early weeds that emerged with the soybeans. I cannot recall the exact crop stage or weed stage, but I now know the purpose was to get them very early when they could be flicked out of the ground but while the crop was resilient enough to stay in place. I remember it was a fun thing to see because the speed had to be fast to get the rotating tines to do their job. I was never old enough to run the machine myself, but I remember watching from the Oldsmobile as we came to the field to deliver my dad lunch or supper.

Inter-row cultivation – or scuffling as it was called – was used to get the weeds from between the corn rows. It could also be set up to throw a little soil at the crop to smother any small weeds. When I think back to it now, I realize how much precision was needed. The success of inter-row cultivation started with straight rows from planting, which was dependent on the marker – a physical disc that reached out half the width of the machine – to help you line up for each pass. This was before autosteer was invented, so cultivating meant keeping the implement as close to the rows as possible without touching them and damaging the crop.

I did not ever do any tillage passes for weed control. I still did some fall tillage for residue incorporation, but by the time I might have been old enough to be trusted with that operation, all in-crop weed control had been replaced by chemicals. I remember going to the meetings where the new herbicide-tolerant crops were being pitched. At the time, it was expected that no weeds would develop tolerance to glyphosate. By the time I was at university getting my agriculture degree, we knew this was not going to be the case.

The merits of no-till

Even with the setback of finding out weeds could develop resistance, farmers, agronomists, and industry were set on making no-till work. My dad was one of the innovators. He and some friends of his made their own custom-built planter with the goal of a one-pass system. The fields looked messy. Not being able to tell if a field was planted because there was still residue covering the surface was a foreign sight on the landscape. However, the goal of less erosion and more moisture retention was a noble one and worth pursuing.

In the early stages it was found that there were some yield drags and that more fertilizer was needed. This makes sense when you step back and think about it: There is more residue on top, with tied-up carbon and nutrients. Until the earthworms increase, and the system reaches a new level of cycling, you will need to put more into it.

In time, we found that organic matter was increasing. This has led many to believe that tillage destroys organic matter. What is becoming increasingly clear is that when the entire rooting zone is considered (two to three feet), the total organic matter is similar. Tilled soils tend to have more organic matter in the deeper layers, and no-till soils tend to have it concentrated in the surface layer. We typically only measure organic matter in the top six inches, so we were missing the redistribution by not tracking the layers below.

The problems of no-till

Last month, I argued for strategic tillage to address challenges such as compaction, nutrient/pH stratification, and amendment incorporation in no-till systems. In the article that ran in our April magazine, I argued that a quicker cycling of the short-lived particulate organic matter (POM) that leads to a greater accumulation of the mineral-associated organic matter (MAOM) can be a win for the farm. By addressing a problem of production, without contributing to another problem (erosion), we can use the proper tool for the job and gain in the years and decades ahead.

Herbicide-tolerant weeds are another problem of production that need the proper tool applied. Left unchecked, herbicide-tolerant weeds will crash your system. This is another place where tillage can be added as another tool in your toolbox. It is not to go back to tillage fully. It is just looking at other ways we can hit back against the weeds that have found weaknesses in our offences.

More tools in the toolbox

To get some ideas for what we can use, we can look to what organic producers are using. Long crop rotations, green manure cover crop years, and perennial phases are the main ways to keep weeds in check. Tillage is still needed while the crop is establishing or to deal with tough perennial weeds. While some have tried to make roller-crimped cover crops work for organic no-till, there are still some challenges in that. Big biomass is needed. In the Prairies, our shoulder seasons just are not long enough for this to consistently work.

Technological advancements in machinery are helping to make big advances in weed control for organic growers. Recall that the experiences of tillage for weed control that I had growing up were in the pre-GPS-guided era of farming. Now that we can have centimetre-level repeatability of passes on the field, we can get much closer to the rows than in the past. We can also have narrower rows that still allow the equipment to pass through. When this is combined with camera-guided implements, we can get much more precise on removing the weeds and saving the crop.

For crops that are drilled in narrow rows, the rotary harrow could still work for you. It is not a rescue tool. You cannot see the weeds getting out of hand and then go into the field. It works best when the weeds are in the white-thread stage. This means the shoots and roots are developing, but they have not yet got their leaves above ground. Disrupt them as they have used up their seed reserves and you will do a lot of damage. This must be well-timed and planned out. Some years when it’s too wet to be in the field it may not be possible to do this.

This year, as you go across your fields, start to think about what you would do if you were confronted with weeds that you could not kill.

Pay attention to the reports of weeds that are showing up in your area that have confirmed cases of herbicide resistance.

Talk to other farmers and to the generations that have gone before you. You might be surprised with the knowledge that is already out there. Herbicide resistance is a real problem, and we must be ready to tackle it before it gets a foothold.

Tillage can be an appropriate tool that, when used correctly, will not undo decades of progress on no-till. BF