Lethbridge Research Centre Report | January 13, 2000
Lethbridge, Alberta - Western farmers have rapidly adopted herbicide-tolerant canola (HTC) systems in recent years, but the benefits of choosing those systems over conventional canola production are not as black and white as farmers may expect.
A recent two-year study at the Agriculture and Agri-Food Canada sites in Lethbridge and Lacombe, Alberta, in Scott, Saskatchewan, and in Brandon and Morden Manitoba, shows that while HTC systems offer a large weed control advantage in most areas, that doesn't necessarily translate into a huge yield advantage over conventional canola systems.
The study compared three widely-grown HTC systems with a conventional canola system using post-emergence herbicides. Overall weed control ranged from 93 percent weed control in glyphosate (Roundup)-tolerant canola, to 84 percent for imazethapyr/imazamox (Odyssey)-tolerant canola, 73 percent weed control for glufosinate (Liberty)-tolerant canola, and 37 percent for the conventional sethoxydim/ethametsulfuron (Poast/Muster) canola treatment.
Overall yields ranged from 49 bushels per acre for glyphosate-tolerant canola, to 42 bushels for imazethapyr/imazamox-tolerant canola, to 40 bushels for glufosinate-tolerant canola, and 38 bushels for the conventional canola treatment.
"The herbicide-tolerant canola systems were not as much of a yield advantage as producers may have thought," says Blackshaw. A big factor was the presence or absence of weeds that are hard to control under the conventional system.
"If you had a big problem with stork's-bill or cleavers, then the herbicide-tolerant system was a huge advantage, because we really couldn't control those weeds at all in the conventional system." he says. "But in most cases, we found that if you control your most competitive weeds, such as wild mustard or wild oats, the yield with the conventional system is not that much lower."
In 1999, approximately 80 percent of the 5.6 million hectares of canola in Western Canada were seeded to HTC. In general, HTCs simplify herbicide application for farmers, offering a broader spectrum of weed control in a form that is easier to apply effectively.
In the study, the most dramatic advantages of HTCs were at the Lacombe and Lethbridge, Alta. sites, where HTCs out-yielded the conventional system by 13 to 39 percent; stork's bill was a large factor at both sites, as was cleavers at the Lacombe site.
"Stork's-bill is becoming more widespread across the prairies, but it's a major problem in Alberta, particularly in east-central Alberta," says Blackshaw. "Cleavers are also a big problem in central Alberta, and they have become more prominent in Manitoba."
At the other end of the spectrum was the Scott, Sask. site, which showed comparable yields in both HTC and conventional systems. It's also important to note that post-emergence application used in the study may be less effective than other herbicide applications producers use with conventional systems, so the performance results of this system are likely conservative, says Blackshaw.
"In some areas, producers using conventional systems are actually attaining similar yields and sometimes realizing more net income because of lower seed and herbicide costs than with HTC systems," he says. "They can do quite well, particularly if they're controlling weeds on their farm in other ways, through rotations and other management."
The wide disparity between the weed control results compared to the yield results also serves as a caution to producers who may be setting their control targets too high, says Blackshaw. "Better weed control doesn't always translate into a higher yield."
However, a clear advantage of the introduction of HTCs is that farmers now have more weed control options, he says. With proper management, that can help the industry develop improved weed control strategies and more sustainable systems. That includes such things as herbicide rotations, which will help prevent the build-up of herbicide-resistant weed species.
