Weed biotypes have an incredible capacity for developing resistance to chemical products and growers are having a tough time keeping up with the changes.
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Some farmers are now battling weed resistance at harvest by attaching seed mills to the rear of a combine, which gather weed seeds and damage them, preventing germination.
Why it matters: The use of seed mills and chemical controls can help growers prevent problem weeds from developing resistance.
Currently, there are four designs of these seed mills on the market. Three are from Australia: the integrated Harrington Seed Destructor (iHSD), the Seed Terminator and the WeedHOG. The Redekop Seed Control Unit is built in Saskatchewan.
The concept of seed mills isn’t really new. Dr. Breanne Tidemann has been working with harvest seed-weed control systems since 2014, first working with the Harrington Seed Destructor as a tow-behind version that’s now fully integrated. She also worked with prototypes of the Redekop Seed Control Unit.
“Anything that’s in the chaff and goes through the mill, it will control greater than 95 per cent of those weeds,” says Tidemann, a researcher at Agriculture and Agri-Food Canada in Lacombe, Alta.
“The trick is actually getting the seeds into the mill.”
“(Required)” indicates required fields
Much of the efficacy in damaging the seed depends on the weed biology and stature, the accompanying crop and the number of modes of action to which the weeds are resistant.
Weeds that are short to the ground and weeds that have seeds that float through the air such as thistles or dandelion are harder to get through the combine. Generally, seed size doesn’t seem to have a large impact as much as the weed biology and when it’s maturing compared to the crop.
Physical damage a long-term concern
If there’s a point to be clarified with harvest weed seed control systems, it’s that crushing, cutting or physical damage will not prevent weeds from evolving.
“I would never say that weeds can’t respond to any kind of weed control,” says Tidemann. “They will find a way, because it’s a selection pressure — it’s what evolution does.”
Researchers expect weeds to respond to physical damage by shifting their biology to drop seeds earlier so they’re down before harvest, for example, or to select for more prostrate forms making it harder to get into the combine. Some of that work has been done already in Australia where they started seeing resistance in wild radish and annual ryegrass, where they’ve been using weed seed control methods for 10 to 15 years.
“It’s why I would encourage using one before it becomes a last resort,” she adds. “If you have two effective (chemical) modes of action, it’s harder to develop resistance to either of them. With herbicides plus harvest weed-seed control, it’ll be harder for weeds to develop resistance and become problematic.”
It’s also why Tidemann believes harvest weed-seed control systems should be part of an integrated approach, with chemical, physical and cultural means, increasing the chances of success.
Whether there’s a definitive percentage of the seed that has to be damaged to prevent germination has yet to be determined.
Sticker shock
The current integrated systems can run upwards of $100,000 or more, depending on the model.
Tidemann notes it’s the cost per acre that’s important. A grower she knows runs a Seed Terminator on four of his combines and factors his interest, financing, fuel and any repairs needed as part of the operating costs.
“He has it broken down based on his 4,000 (owned) acres and it costs him $6.50 per acre,” says Tidemann.
“It started higher but based on what he’s spent and how many years he’s used it and the repairs, it’s down from $10.00 when he was first using it.”
