Mechanical weed control is not anything new. Farmers have been using harrows and various tillage tools to control weeds for centuries, and for organic farmers mechanical weed control remains the only option.
What is new is the technology that is available to help make mechanical weeding more efficient and effective, like GPS or camera-guided systems and inter-row cultivators to more accurately target weeds between crop rows, although few systems deal effectively with weeds in the crop row without disrupting the crop itself.
Researchers at the University of Manitoba, in collaboration with the Manitoba Pulse & Soybean growers, have been comparing various levels of herbicides with different mechanical weed control methods to see which are most effective at controlling weeds in edible beans. They’ve looked at: an Einboeck Aerostar tine harrow, a traditional harrow, a rotary hoe, an inter-row cultivator and a camera-guided Garford Robocrop InRow system.
“You can think about mechanical tools and how they work similarly to herbicides,” says the project’s lead researcher, Katherine Stanley. “You have selective tools and non-selective tools. The inter-row cultivator is selective and ideally, the implements, the shanks, don’t come into physical contact with the crop because it stays in-between the crop rows. Whereas something like a rotary harrow or traditional harrow is non-selective, because it runs over the whole crop, so timing is more crucial because you want to maximize weed control while minimizing crop damage.”
Timing is crucial
This research, and prior work Stanley did in Saskatchewan in organic pea and lentil crops, concluded that inter-row cultivation gives producers the option to also control weeds later in the growing season because they are only targeting inter-row spaces for weed control. Harrows are more effective earlier on, when weeds are at the white thread stage.
“The weed stage is important, and it’s hard to give any definitive conclusions because the last couple of years have been so different in terms of the weed species and flushes, but that’s why it’s important for producers to make sure they are in the field and scouting so they can properly time mechanical weeding,” says Stanley.
The most effective weed stages for tools like the harrow or rotary hoe is the white thread stage before, or just as the plants break the soil surface. “Move some soil around with your fingers and you will see lots of white little roots at the surface, and that’s a really effective stage for managing weeds,” says Stanley.
The inter-row cultivator is able to control larger weeds further on in the season because it is more aggressive and its undercutting action slices weed roots and either buries them or leaves them on the surface to dry.
“But you still want to control them at a point where they aren’t compromising the yield of your crop,” adds Stanley.
Integrating systems works best
Work at the University of Saskatchewan led by Dr. Steven Shirtliffe has shown that integrating some of these mechanical methods can give better weed control.
Combining different methods of mechanical weed control in organic lentils showed that a minimum till rotary hoe followed by inter-row cultivation worked the best, on average decreasing weed biomass by around 76 per cent and increasing seed yield by around 55 per cent. Increasing the seeding rate also increased yield by an average of 30 per cent, so combining increased seeding rate with the rotary hoe and inter-row cultivator increased seed yield by around 70 per cent and decreased weed biomass by around 80 per cent. But these methods were relatively ineffective on perennial weeds.
In her study, Stanley has been impressed with all the mechanical weeding tools, but agrees that producers are likely going to need to use them in combination to effectively control most of their weeds.
“I think there’s a lot of utility in the inter-row cultivator but you’re not necessarily having perfect control of the weeds that are within the crop row,” says Stanley. “That’s why I think the harrow or the rotary hoe or something that is non-selective early in the season to control the weeds within the crop row is important.”
For 2019, the trial included beans on wider row spacings and with finger weeders attached to the inter-row cultivators that could go into the actual crop row to try and control weeds there.
Finger weeders are cylinder shaped attachments with eight flexible fingers, driven by a small wheel that goes into the ground.
“What’s unique is that it’s not actually being driven by the pressure on the finger weeders, it’s being driven by the centre of the cylinder,” says Stanley. “The finger weeders go into the crop row at the base of the plant and bend a little bit so they’re flush. They are able to move in the crop row and not uproot the beans, but bury or uproot small weeds.”
Stanley was impressed with the finger weeders. “They did a good job,” she says. “Putting beans in wide rows makes a lot of sense if you have these types of tools.”
Narrow row spacings
In trials on narrow row spacings for edible beans, the camera-guided Robocrop InRow weeder definitely shone. “Because it’s camera guided, you can use it on very narrow rows whereas you can’t really steer that by eye, although on some of the larger cultivators, when you’re on a wider row spacing, your GPS usually provides enough accuracy,” says Stanley.
“Last year we had later weed flushes and weren’t able to control the weeds within the actual crop row, so it became really problematic in a crop like beans where there’s quite a bit of space in-between each bean in the actual row as opposed to a cereal crop that’s more competitive and can outcompete weeds in that zone.”
Generally, says Stanley, producers can use these mechanical tools on wide or narrow row crops, but they need to understand what the challenges will be with each system and make sure they are scouting for weeds and time weeding appropriately.
“With any mechanical weeding tool, you are disturbing the soil and your crop canopy, so it’s important that when you are using these tools that they’re as effective as they can be. Scouting goes a long way in helping with that and especially to assess proper timing of weeding,” she says. GN