Researchers say herbicide layering tactics and high seeding rates can help growers protect yields with clean fields
Weed and disease management is challenging in pulses, so it’s difficult to know where to draw the line when it comes to how many inputs to apply.
“A lot of the work that we’ve been focusing on is what type of inputs should we be recommending for producers to try and manage these challenges,” said Jessica Weber from the Western Applied Research Corp.
She said lentil production relies heavily on Group 2 herbicides, but weeds such as kochia and wild mustard have developed resistance to that group of chemicals.
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To help relieve pressure from herbicide-resistant weeds and to prevent further resistance development, Weber said growers should use one of the layering options rather than just using a pre-seed burndown.
She said pre-seed residual products work especially well when growing pulses.
“Herbicide layering is when we’re using multiple herbicides in sequence, and using different groups to tackle these herbicide-resistant weeds,” Weber said.
“A lot of these products are soil-residual products and it really helps aid that early weed control.”
Many of herbicide products that are used for layering in Western Canada have been researched by Christian Willenborg at the University of Saskatchewan, and he’s currently examining how to control canola, mustard, and kochia in lentils with herbicide combinations not currently registered.
“What we found is metribuzin, which would be your Sencor, when we applied it in the spring pre-seed in lentils is really effective,” Weber said.
“But when you combine it with different options like Edge or pyroxasulfone, which would be like Zidua, we’re finding that our efficacy really increased.”
She said with just a fall application of pyroxasulfone, there is a reduction in mustard and canola weeds but they are still quite prevalent, but when a spring metribuzin was included there was a significant reduction in the amount of weeds.
“This particular combination is not registered at the moment, but it’s just showing that the efficacy of using multiple products is quite efficient,” she said.
Weber is involved in a separate lentil study that’s been running since 2017 in five locations in Saskatchewan.
Seeding rates of small red lentils started at the current standard of 130 viable seeds per sq. metre, and then rates went up to 190 and 260 seeds per sq. metre.
For weed control there was a check with no herbicides, glyphosate applied alone and then glyphosate with Focus, which is a residual herbicide.
The study also had three disease control treatments including no fungicide, a single fungicide application and a dual application.
“In 14 site years, in 10 of them, the residual herbicide worked better than with glyphosate alone; 71 percent of the time it worked,” Weber said.
“We found about a 66 percent increase in our annual weed control, anything from volunteer canola, kochia, cleavers, green foxtail, things that are on the label.”
She said in the 29 percent of the time in which treatments with the residual were no better than glyphosate by itself, it was largely because the weeds on the plots were outside the residual control spectrum, including Canada thistle.
Researchers looked for the effect of seeding rate changes and the effect of herbicides, in relation to weed biomass as well as weed densities.
“There is actually a very strong interaction between the two. When you have 130 seeds with typical glyphosate application, we had the highest amount of weed density as well as the highest amount of weed biomass,” Weber said.
“When you compared it with the regular seeding rate with Focus, there was a 65 percent reduction. When you go to 190 with the Focus added, there was a further 33 percent reduction.”
By far the best treatment was a seeding rate of 190 per sq. metre, with both glyphosate and Focus applied.
The check with a 130 seeding rate and no herbicide treatments had five weeds per sq. foot, which Weber said is very low compared to most lentil fields on the Prairies.
Using equations that correlate weed density, weed biomass and yield loss, the check had about five percent yield loss while the ideal treatment with herbicide layering and a 190 seeding rate had only a one percent yield loss.
The check had a nine-percent yield loss at 10 weeds per sq. foot, while ideal treatment had only a three-percent yield loss.
“There is a significant interaction between your seeding rates and your fungicides,” Weber said.
“At 260 seeds per metre squared, what we found was that unsprayed was obviously the highest, but even with that dual application you’re still at a fairly high risk for disease.” However, she said at the high yield sites, growers can increase their seeding rate to 190, as long as they focus on their fungicide program.
“The reason I want to highlight 190, is because as soon as you start getting to 260, you really start opening yourself up to disease risk,” Weber said.
“190 is kind of that sweet spot where you are still getting that yield but you’re not opening up yourself to that large disease risk.”
She said a similar trend was seen at the low yield in sites, but at the 260 seed rate there was a yield loss compared to 190 seeds rate because there wasn’t enough moisture to sustain such a dense crop.
To sum up, the study found the optimal input was to increase seeding rates to 190 plants per sq. metre, use a residual herbicides in addition to glyphosate, and use at least one application of a fungicide.
