MOOSE JAW – Broadleaf weed control in lentils is notoriously difficult, even in conventional cropping systems using herbicides. In organic lentils, mechanical control is the only option.
Before certifying as organic, Cal Cowan from Moose Jaw had used a weed wick, a Roundup-soaked rope pulled above his lentils, to control weeds.
“When we went organic, there was zero control.”
Cowan said Dwayne Woolhouse, an organic farmer near Assiniboia, Sask., had built a belt-driven mechanical weeder on a swather.
“It worked pretty slick, so I talked to him, looked at it and got the OK that I could build one. He was very helpful and gave me some hints on what he had tried, what worked and what hadn’t. So we proceeded to build what we’ve got now.”
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Cowan chose to use a combine instead of a swather, and put hydraulic motors on the weeder rather than using a belt drive because he wanted a bigger one with power.
He felt a pull-type whacker would knock down the weeds before they got chopped. He preferred something out front. A combine has the table out front, provides good vision, has hydraulics available and includes a cab with air conditioning.
Cowan’s weed whacker started out as a 1974 F2 Gleaner. The original gas engine still powers the unit and provides hydraulics for steering, lifting the boom and putting it into transport.
A second engine came from another old Gleaner combine. It was a diesel with 160 horsepower and its only job is to power the hydraulic pump for the weed whacker blades.
“We pulled the hopper off the combine and mounted the diesel motor where the hopper was. There’s no (harvesting) parts in the combine now. Everything was removed for a weight factor,” said Cowan.
“We got a hold of Hy-Power in Regina and they did the specs on everything we were going to need – the amount of oil, horsepower on the engine, type of orbit motors and speed. They did a schematic for us on how to hook it up. That saved a complete nightmare for us, to try and plan something and not have enough oil pressure or the pump wasn’t big enough.”
Cowan bought the biggest hydraulic pump he could get and mounted it directly to the engine crank. A 200 gallon hydraulic oil reservoir is mounted underneath where the chaffer used to be.
“It’s underneath, so it keeps a little cooler there. There’s also a cooler on the side of the combine that keeps (the hydraulic oil) cool. It’s a separate radiator mounted next to the tank.”
One large hose feeds the hydraulic pump, while two smaller hoses return the oil to the reservoir.
Cowan removed the combine header and built a completely new platform that carries 18 steel blades, each 27 inches and powered by an orbit motor.
“We built our own platform, with about 12 feet in the centre, with hinges and two track wheels on the end of each boom to track the contour of the land. It can be lifted up with hydraulic rams for transport,” he said.
“The blades turn at 2,800 rpm, the same as a weed whacker. We’ve got tiny shear pins in them, so if a blade hits anything, it deadens it and drops the blade down. It doesn’t fly out or anything.
“The frame that holds all the blades is made out of U-channel, 3/8 inch thick and a foot wide. If I did it again, I’d probably do it out of tubing. But we overbuilt it to be on the safe side.”
The orbit motors are mounted right to the deck. Rubberized cushioners, where the motor shaft joins the blade shaft, provide a bit of give.
“If you hit something, it’s not a big jolt and it won’t break the shaft on the orbit motor. Then we went with a double bearing system on that shaft, separate from the motor shaft, for stability and strength. There’s a lot of torque on the end of those blades.”
Cowan added puck board covers on the boom to protect the orbit motors from flying debris. He said chopped up weeds tended to pile up, but with the covers, the motors run cooler.
In the cab, Cowan has a flow control unit to start and stop the hydraulic pump. While it can control speed somewhat, he uses it to start and stop the cutting blades.
Where the boom attaches to the combine, Cowan added a tilt control hydraulic. This allows him to adjust the boom to keep the blades level as the boom lifts or drops.
Each blade is a piece of quarter-inch flat metal. Sharpening the blades would make a clean cut on the weeds, which Cowan wants to avoid.
“We don’t want a clean cut. We want to fracture the stalks. In mustard or kochia, it smashes the stalk so it won’t come back again. With a clean cut, the plant will come back,” he said.
“On wild oats, they will still come back. I’ll go over it twice if I’m after wild oats. Just when they start to head out, I’ll hit them. Then about a week later they’ll start heading again, but with not as many heads or kernels. I’ll hit it one more time, then I’m ready to swath, so it won’t set seed.”
Cowan makes his first trip into the field with the weed whacker as soon as it starts to look dirty, usually about 60 days after seeding.
“When the lentils are probably at their full height, I’ll go out. You’d like to go out sooner, but then you’re into more trips. I like to hit it twice and then I’ll swath. I’ll wait a while once it comes up, then hit it and hit it again about 10 days later. Then we’re into swathing,” he said.
“I’ll almost nick the tops of them, but you don’t want to take the tops off the lentils. (The blades are) spinning so fast you can almost see the lentils moving underneath from the air pressure.”
The weed whacker has a height guide in the cab set from one to 14 inches.
“We’ll set it at, say, seven inches for french green lentils. Then we’ve got guides on the outside wheels we can raise and lower to whatever the height the lentils are and a half inch higher. It’s like a header adjustment control.”
Cowan considered going with narrow tires on the combine, but found the original tires worked well.
“It’s a small combine and they’re small tires. With the wider tire, the lentils seem to pop back up after you go through.”
Moisture conditions dictate how fast the operation proceeds. With a 40 foot boom and a field speed of six or seven mph, he can often do more than 30 acres an hour.
“When the weeds are wet in the morning, you can’t go. If you’ve got mustard and it’s fairly heavy, you can’t get going until about 11 in the morning. You’re only doing a mile an hour, but if you wait until it dries out, you can boot it along.”
While the weed whacker was initially built for weed control in lentils, Cowan said he has found all sorts of other uses.
“We use it in lentils, peas and flax. If you’ve got thistle patches, it’s a nice way of mowing it and you don’t leave so much tracking. If you had kochia in cereals, you could go out before the crop got too high. But once it’s headed, you’re done,” he said.
“If your summerfallow is getting away on you, or if you have thistle patches in your durum, you just drop it right down. We’ve got a stripper header that takes the heads and leaves three feet of straw to catch snow. So we put the whipper on that to chop the straw in the spring.”
Cowan has invested about $35,000 in his mechanical weed whacker. If he was going to build another, he said he’d probably use one larger motor for everything, instead of the separate gas and diesel engines.
“I might design the front a little different, but there’s not a whole lot I’d change on it.”
