WGRF research offers faster herbicide testing

WGRF-funded research offers a rapid test to determine whether your weed escapes are Group-2 herbicide resistant

You sprayed 10 days ago and yet that patch of wild oats is still thriving. So you do what farmers across the Prairies do in this situation: take a sample and send it in to the Crop Protection Lab (CPL) in Regina and wait.

Depending on the problem, some answers come in just a few weeks. But sometimes you wait months to find out what exactly is going on with those weeds, unable to make an informed management decision until you do.

Hugh Beckie, research scientist with Agriculture and Agri-Food Canada (AAFC) explains why.

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“The Crop Protection Lab only has facilities to do soil-less tests, so they can only do certain tests, such as Group 1 FOP and DIM tests — so any Group 2 or Group 1 DEN tests had to be done here,” he says, referring to AAFC in Saskatoon.

Those tests take time because, Beckie says, AAFC uses traditional screening methods (growing suspect seeds in pots in greenhouses and spraying the resulting plants), in order to have standardized data on the depth and breadth of the resistance situation across the West. Add to that the sheer volume of samples sent in for testing — over 400 in the last crop season alone — and you can see where bottlenecks can occur.

But as herbicide resistance spreads and becomes more complex, there will only be more samples, and farmers will need timely answers on all suspected weed populations so they can make timely management decisions.

With funding from Western Grains Research Foundation (WGRF), SaskPulse and Saskatchewan’s Agriculture Development Fund (ADF), Beckie, along with Jeff Schoenau and Anna Szmigielski at the University of Saskatchewan, set out to see if they could develop some testing methods that would help speed things up a bit.

Groups and classes

First, though, let’s start with a quick primer on the nuances of herbicide groups. Farmers already know that herbicide groups are based on modes of action. But within each group, there can be smaller chemical families known as classes — they all kill weeds using the same basic biological approach, they just do it slightly differently.

Group 1 herbicides have three classes: DIM (clethodim, sethoxydim), FOP (fenoxaprop, clodinafop) and DEN (pinoxaden). Group 2 herbicides have five classes.

Rapid assays to detect Group 1 FOP and DIM resistance in wild oats and green foxtail already exist and are being used at the CPL in Regina — those are the results you get back quickly. The task that Beckie, Szmigielski and Schoenau set themselves was to develop new test protocols for Group 1 DEN and the Group 2 classes on key problematic grass and broadleaf weeds (wild oats, green foxtail, cleavers and wild mustard).

“Developing the DEN test was fairly straightforward because we were able to adapt it from FOP and DIM tests,” says Beckie. Researchers experimented to determine which parameters worked best, such as what herbicide concentrations were the best indicators of resistance and of susceptibility (equally important information for farmers), but essentially, the new rapid DEN tests they developed use the same methodology as existing tests for other Group 1 classes.

Weeds in a pouch

The Group 2 tests were a different kettle of fish. The soil-less testing methods used to successfully develop Group 1 rapid bioassays didn’t work for the Group 2 classes, so Szmigielski and Schoenau began to look at a soil-based protocol called the soil pouch assay.

“It’s still soil, but much less than we’d use in the greenhouse work,” says Beckie. “It’s quite a departure from the past in terms of resistance testing.”

In a nutshell, a mere 50 grams of soil, moistened and spiked with a Group 2 active, is put in a small bag. Suspected weed seeds (in this case, cleavers and wild mustard) are planted two mm deep, and the bags hang upright on a frame allowing the seedlings to grow as they would in a field. After a few days, the plants are taken out, the soil is washed away and the roots are examined. Root length inhibition — how long the roots grow in the spiked soil — is an accurate indicator of herbicide resistance or susceptibility.

As with the soil-less tests, the U of S team experimented to find the parameters that would ultimately define the final testing method: herbicide concentration (different for each class within Group 2), number of seeds per bag, optimum number of days for growth, and so on.

At the end of the three-year study, the team had successfully developed a rapid assay for Group 2
resistance in wild mustard and cleavers. “It’s a mixed blessing,” says Beckie. “This test is likely adaptable to other broadleaf weeds, but we didn’t get it to work well on wild oats, so we’ll keep working on that.”

Even so, he says the Group 2 rapid assay is a game changer.

“The Group 1 assay is really an extension of existing tests,” he says. “The real breakthrough was in the Group 2 tests because, worldwide, there isn’t a Group 2 quick assay, and that’s what most resistance cases are worldwide — Group 2. It’s a landmark in research. I’m sure it’s going to be adapted and adopted around the world.”

The new rapid assays are ready to go now, says Beckie. “There will be a more rapid turnaround time from when farmers submit a sample to when they get a result, and that’s the most important benefit,” he says. “The cost should also come down.”

WGRF is a farmer-funded and directed non-profit organization investing in agricultural research that benefits producers in Western Canada. For over 30 years the WGRF board has given producers a voice in agricultural research funding decisions. WGRF manages an Endowment Fund and the wheat and barley variety development checkoff funds, investing over $14 million annually into variety development and field crop research. WGRF brings the research spending power of all farmers in Western Canada together, maximizing the returns they see from crop research.

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