A new bioherbicide developed by researchers at the Agriculture Canada Research Centre in Saskatoon may offer farmers and homeowners a “reduced-risk” alternative to chemicals such as 2,4-D for killing broadleaf weeds.
Karen Bailey, a research scientist specializing in biological control of weeds and plant pathology at Ag Canada in Saskatoon, said the “new tool in the tool box” is a fungus called Phoma macrostoma that was first discovered on Canada thistle in 1996.
“We found that when we sprayed it onto plants it didn’t do anything. But when we put the organism in the soil, it would infect the roots and turn the plant white. When plants go white, they die because there’s no chlorophyll,” said Bailey, who received the Canadian Phytopathological Society Award for Outstanding Research for her role in the discovery.
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The award recognizes Canadian research involving new concepts, discovery of new phenomena and principles in plant pathology or novel application of existing principles.
For the last 15 years, Bailey’s research has focused on how fungi can suppress weeds, especially those having significant economic impact. After a few years of testing, in 2001 the researchers realized they had a potential winner on their hands and filed a patent.
Phoma is now being developed as a granular bioherbicide for soil application. It will be a “green” substitute for 2,4-D type herbicides and can deliver the same degree of control as the chemical standard.
Registration of the product for general consumer and agricultural use is underway, and a deal has been inked with the Scotts Miracle-Gro Company, the world’s largest marketer of branded consumer lawn and garden products, to produce and market the product.
Bailey said within two years it will become available for agricultural use, once it clears testing, regulatory and registration hurdles.
The fungus has no effect on monocot grasses, a group that includes all common cereal crops, but has a powerful effect on plants in the compositae family, such as dandelions, thistle and scentless chamomile, as well as clovers and brassica weeds.
“We see an application in agriculture, because in cereal crops, Canada thistle is a very significant problem, especially for organic producers,” she said.
In testing at Agriculture Canada’s research station in Beaverlodge, Alta., the product was found to be effective in controlling hawksbeard, wild mustard and other common problem weeds in the area.
Using Phoma macrostoma to control weeds works well in crop rotations, Bailey added, because the fungus is not competitive and doesn’t survive for long periods in the soil after application.
It is broadcast onto the surface, and then rain and moisture filter it into the soil and the root zone where it can attack the roots of target plants. Once the weeds die, the fungus also dies because it requires a host to survive. The microorganisms within the soil ecology then gradually gobble up what’s left because it is unable to compete with them.
“We’ve done a lot of environmental studies. A month after we put it out, we can see that it is present in the soil. Two months later, we can see that it has actually increased and is at its strongest point. At four months, we start to see the populations decreasing, and at 12 months we can’t detect it at all anymore,” said Bailey.
Lentils and canola planted the following year have shown no adverse effects on fields where the product was used, she added.
“It will work terrific for agriculture in rotational systems.”
Production of a bioherbicide, typically through fermentation, is a little trickier than mixing chemicals derived from petroleum, which means that it will be more expensive. Because it is a living organism, more work is required to determine the best way to mass produce it and allow it to remain in a useful and viable state in storage and during transport.
“I don’t think it will be as cheap as 2,4-D, but it will be cost-effective and in a price range that people will accept,” she said.
Phoma macrostoma does its work in the mycelium stage and although it does produce a kind of spore, apart from the small risk of rain splash, it is unlikely to spread and affect neighbouring crops.
Testing has shown that it is safe for humans, because it cannot tolerate temperatures above 35 C.
“Our body temperature, of course, is 37.5 C, so it could never infect us because it cannot exist at that temperature. There’s no buildup, no residue and no persistence.”
Toxicology testing for its safety regarding honeybees and earthworms has shown no ill effects.
Bailey and her team are pioneering Agriculture Canada efforts to develop other “reduced-risk” alternatives to conventional herbicides. Bioherbicides, like their chemical counterparts, are regulated by the Pest Management Regulatory Agency of Health Canada.
New bioherbicide products for registration in Canada and abroad in the pipeline include Pseudomonas bacteria for controlling green foxtail and wild oats, as well as another fungus, Colletotrichum truncatum, for controlling scentless chamomile in lentils.
