A Herbicide Guide to Help You Decide

Story written by Geoff Geddes | The Word Warrior

Some decisions are easy: sink or swim; do or die; snake pit or petting zoo. Others, like choosing the right herbicide for the job, can be more involved. To aid growers in this dilemma, researchers set about creating a helpful guide with the project "Developing decision support tools for effective herbicide use in the face of herbicide resistance".

“One of the most commonly recommended practices to aid in the delay of resistance development is the use of tank mixes with multiple effective modes of action (MEMOA),” said Dr. Breanne Tidemann, research scientist, Weed Science, Science and Technology Branch, Agriculture and Agri-Food Canada (AAFC) at the Lacombe Research and Development Centre. “This involves including more than one effective herbicide group in a tank mix for target weeds.”

While this is a simple strategy in theory, the execution can be more complicated for producers. Herbicide marketing refers to many products as “resistance management tools”, and the words “multiple modes of action” are often targeted in advertisements.

However, just because a product contains multiple modes of action, it doesn’t mean that those modes are all effective on a target species.

Clearly, a tool was needed to help navigate these murky waters, and the point was driven home for Tidemann at an Agronomy Update in Red Deer several years ago. As part of a talk on using multiple effective modes of action, she spoke about those myths that often appear in marketing, and even gave a quiz on the topic. Participants were quick to query why there was no decision support system to help in this area, and Tidemann promptly shared her response: “Good question!”

Though she would likely choose another adjective, this was where things got “interesting”.

“Initially, we thought we had an industry partner lined up with an existing database that we could use for the project, but that was not the case. As a result, we had to go back to the drawing board and enter every herbicide, mode of action, weed controlled and tank mix partner.”

For this process, they pulled information from the Pest Management Regulatory Agency (PMRA) database, the government agency responsible for the regulation of pest control products in Canada. Unfortunately, that approach was more complicated than it first appeared.

“At the outset, we tried to focus on just the herbicide labels for what tank mixes should be used. For liability reasons, we can only recommend what is registered. This proved problematic, however, as often one herbicide would have a tank-mix registered, while its tank mix partner or partners did not have it on the label.”

To further cloud the issue, some products can, for example, be mixed with any MCPA option, while others may only be combined with MCPA 600. Certain herbicides are mixable with glyphosate, but not glyphosate salt, or only with specific glyphosates.

Okay, but at least it couldn’t get any more frustrating, right?

Well…

“in the course of our work, we found there is so little consistency in the terminology for herbicide labels. Some labels will be very specific, such as ‘ good for use on redroot pigweed’, while others will just refer to pigweeds in general; one will use the scientific name, whereas another lists the common name. The technician working with me tried to write some computer code so he could run herbicide labels and the program would automatically pull key information from them, yet that is hard to do when all the labels are done differently. The basis for the project seemed like a straightforward concept until we started in on it.”

If it all sounds convoluted, there’s a good reason for that, yet it’s also a testament to the patience and persistence of researchers in support of the end user.

“When the project is done, we will have a browser-based app that producers may access via an online link. They can then enter the crop, the weed they are targeting, the product they are hoping to use and any herbicide resistance they know of in their field regarding that weed. From there, the app will identify the tank mix partners they can use to provide a second effective mode of action on that target weed.”

By employing the app, growers with problem weeds in certain fields should be able to forge a herbicide management plan and more effectively integrate multiple effective modes of action in their system with greater confidence.

“In the process, we hope to delay the further development of herbicide resistance in weeds of interest. It is too late to eliminate the resistance that exists today, but at least we can try and keep our current herbicides effective as long as possible.”

While success in research is always the goal, Tidemann is especially heartened by the implications of this study.

“For me, there is more of a knowledge transfer element here than in a typical project. Ultimately, we are taking something and helping farmers use it more effectively, and that’s kind of cool. As an added bonus, we may come out of this with some recommendations for herbicide labels going forward, so we don’t have two Latin names and four common names all tracking back to the same weed.”

Given the confusion around labels, the team may go even further to address variability.

“There are aspects of herbicide recommendations in the Blue Book and herbicide labels that have also added complications. [Produced collaboratively by three of Alberta’s crop commissions – Alberta Grains, Alberta Canola and Alberta Pulse Growers – the Blue Book or crop protection guide is a comprehensive, up-to-date resource for the selection and application of chemicals to protect crops]. That guide (and the labels) list some tank mixes as ‘supported but not registered’, so what do we do with that? If it’s a common tank mix for farmers, we’d like to facilitate its use, but we don’t want to assume the liability that may arise.”

In a project of this complexity, Tidemann felt the last word should go to her unsung heroes.

“I must give a ton of credit to my research technicians - Christine Cock and Gregory Innes – and to Virginia Farewell, who has been working on some data entry of late. They performed a lot of the footwork and manual entry required in this project. It was often mind-numbing work, and I admire their tenacity.”