Wild oat management is an ongoing battle for farmers in Western Canada. According to Hugh Beckie, an Agriculture and Agri- Food Canada research scientist whose field of expertise is herbicide- resistant plants, wild oats is the most important weed from an economic viewpoint on the Prairies after green foxtail. “Not only that,” says Beckie, “increasing herbicide resistance in wild oats is a pressing problem.” Steve Shirtliffe, a professor at the University of Saskatchewan concurs. “The resistance issue is a concern,” he says. “It’s abysmal in Manitoba where large numbers of fields have resistant wild oat populations.” Nasir Shaikh, provincial weed specialist with Manitoba Agriculture, Food and Rural Initiatives, also views wild oat management as an ongoing management process that farmers need to be very much aware of.
Managing wild oats is then a key aspect of the business of farming. All the experts agree there are some important tools farmers have in their “tool box” that they need to be using judiciously in order to control wild oats and minimize their risk of developing or further building numbers of resistant populations of wild oats. “Integrated weed management is what farmers need to be thinking about,” says Shaikh. “Bringing to bear all the options, agronomic and chemical, to combat this serious weed problem.”
Getting into the field and getting a pre-seed burn-off completed as close as possible to seeding is key. “Do not be lackadaisical about this pre-seeding treatment,” says Shirtliffe. “If for whatever reason you didn’t get to seed right after this treatment, (spray) again. Seeding into a weed-free seedbed is critical in wild oat management.” Beckie agrees with Shirtliffe and adds, “if resistance is an issue you have to deal with, time the burn-off treatment to when the wild oats are emerging to get more of them.”
“Seeding rate is the big hammer in managing crop competitiveness,” says Shirtliffe.
Shirtliffe referred to Charles Mohler at Cornell University and the work he has done in weed ecology and management. “According to Mohler, a good rule of thumb is a 50 per cent increase in seeding rate will have a substantial effect on weeds without any adverse impact on crop quality.” The real key here is to get the crop growth ahead of the weeds, and have the canopy cover the ground as quickly as possible. “Size really does matter,” says Shirtliffe. “Getting the crop off to the best possible start and having enough plants present to get the ground covered and the canopy filled in as quickly as possible is very important.”
“Fast-growing, aggressive varieties be they cereals or broadleaf crops is important,” says Shaikh. “Growing a forage crop like alfalfa is a very good option. Farmers could see a reduction in wild oats of about 80 per cent without incurring any chemical costs at all (by growing the alfalfa in rotation).”
There is a range of management strategies that together give the crop the advantage at the outset. “Good seedbed preparation and good soil-to-seed contact are important,” says Beckie. “Also, we recommend banding fertilizer versus broadcasting to target it to the crop.
In situations where wild oats is a known problem in particular, farmers should be watching row spacing. “A narrower row spacing, eight inches versus 14 to 15 inches, can have a lot of impact,” says Shirtliffe. “The wider row spacing allows more light to the ground and it takes substantially longer for the crop canopy to close. It’s at that point the crop really takes the advantage over weeds.”
Wild oats emerge over a protracted period through May, and that slows with the onset of summer heat. “By using all the tools at your disposal up until the crop canopy closes over, you’ve really gone a long way to reducing the potential severity of the problem you may face in-crop with wild oats,” says Shirtliffe. “But the reality is you can do everything right, but you will still get some wild oats emerging and causing a problem,” Shirtliffe adds. “In this case, then in-crop herbicide application is an option, if you don’t have a resistance problem, but I encourage farmers to think of this only as a cleanup act.”
Farmers have a range of herbicide options ranging from pre-seeding and post-harvest burn-off applications, to in-crop applications with a range of active ingredients from herbicide Groups 1, 2 and 8. Table 1 outlines the herbicides available in each group. “In an ideal world, we don’t want farmers to have to rely on in-crop options, especially as the wild oat resistance problem is so serious and prevalent,” says Shaikh. “Farmers should view these options as supplementary to agronomy and cultural practices.”
Shaikh also advises farmers to invest in testing for resistance problems on an ongoing basis. “A resistant population doesn’t happen overnight,” he explains. “Most farmers are unaware they actually have a problem until the problem exists in about 30 per cent or more of the field. Given this is a growing problem, testing annually should be considered. Think of it as an investment in your overall management strategy.”
The sum total effect of the above five tools should mean the minimum amount of seeds being returned to the soil every year. Wild oat seeds are not as persistent in the soil as might be believed. For instance, compared to wild mustard or pig-weed seeds, which can survive in the soil for decades, wild oat seeds are relatively short lived at about five years or less.
RECOGNIZING AND MANAGING RESISTANCE
Beckie discusses how you know if you have, or are developing a resistant wild oat problem. “There are some signs you can be looking out for,” he says. “If wild oat is the only weed on the label not being controlled you might have an issue.” Typically, resistance first appears as patches of the uncontrolled weed. “Go back to your field records and look for repeated use of herbicides from any one group,” advises Beckie.
If a farmer notices a patch, and determines it could be resistant, what does he do? “The patches start off pretty small usually,” says Beckie. Shirtliffe adds that the biggest issue is that patches might not get noticed until a fair portion of the field shows the problem. “I think some farmers deny the problem thinking they did something wrong, but that’s not the case,” says Shirtliffe. “Wild oat resistance is not a scarlet letter you have to wear on your chest. It’s the nature of the business of farming today. Farmers need to do all they can to prevent the problem, but then be vigilant and act decisively when they notice a possible problem.”
Managing the patch is important. “The goal is to prevent seed rain,” says Shirtliffe. The patch can be mowed out to prevent seed set. “Whatever you do, don’t combine the patch if you can avoid it,” says Beckie. “Once you combine it a patch will spread very quickly. And use modern technology to your advantage. Map the spot with a GPS — many farmers are using this technology now. Map it for future monitoring and special attention.”
There are labs that will test for resistance, so a farmer can be absolutely sure what he’s dealing with. Beckie mentioned two; Crop Protection Lab in Regina, Sask., and Ag Quest at Minto, Man. There are more and they can easily be located using the Internet.
AndreaHildermanhashermaster’sdegree inweedscienceandisamemberofthe ManitobaInstituteofAgrologists.Shewrites fromWinnipeg,Man.
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