A two-year study at the University of Saskatchewan has verified that four products registered for cereal crops that aren’t registered for control of round-leaved mallow do in fact provide acceptable levels of control for that weed.
Ken Sapsford, a research assistant at the Crop Development Centre at the U of S, said the study was launched because round-leaved mallow was beginning to become a problem on some of the university’s research land.
“A lot of the breeders started to have it show up in their plots. When they’re doing the breeding work, they have a very open canopy, with a sparse population in some of the new crosses,” said Sapsford.
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“They’re also putting a small amount of irrigation on to keep things growing. That’s an ideal environment for round-leaved mallow.”
While there are a number of products registered to control the weed, researchers wanted to see what other options might work in their plots. With a substantial weed population already present, Sapsford said it was easy to do.
“We decided to look at some of the newer products on the market to see what they’d do for control on round-leaved mallow. We’d generate that information for farmers, as well,” he said.
“It’s not a weed that’s all over the place. Farmers that do have it, it’s usually been spread by manure being spread onto the land. It seems to come out of the barnyard that way. It is on some fields and can be a major problem, but it’s a weed a lot of the major companies haven’t done a lot of work adding to their label because it isn’t a major weed across a lot of acres. So we’re adding a little bit more information and getting it out there to the producers.”
Sapsford said products registered for mallow control include Attain, and products with a mix of dichlorprop and 2,4-D, like Turboprop 600, Dichlorprop-D and Estaprop. Products registered for suppression include Refine Extra and Dyvel DS.
Initially, the trial tested nine products, which dropped in the second year to five products.
“We took the five that were looking the best from the first year. We dropped off four products that would give us a little bit of suppression at certain application times, but they weren’t consistent for control.”
Products dropped after the first year included Dyvel DS, Estaprop, Frontline and Trophy. Sapsford said these products gave little or no control of mallow when applied at the one- to three-leaf stage and only suppression, or 70 to 80 percent control, when applied at the four- to six-leaf stage.
“What we found in the first year, 2002, when we applied it at the one- to three-leaf stage, which we expected to get better control, a number of the products were poorer at that stage. The reason was they controlled the weeds that were there, but the round-leaved mallow flushed shortly after the application. So any products with no residual whatsoever had poorer control in the early application,” he said.
“Products like Dyvel DS, Estaprop, Attain, Trophy, they did not control it as well as products like Spectrum, Refine Extra + 2,4-D, Frontline 2,4-D, because all of those are short-term residual Group 2s.
Refine Extra has a very short-term residual. It’s not something we need to worry about recropping, but it does give a little bit of residual weed control. The half-life of Refine Extra is seven to 14 days.
“With Frontline, it has a product florasulam that has a short-term residual. What we found is when applied early, they gave a residual control so those late flushings of round-leaved mallow were controlled with those products.”
What surprised Sapsford was how good the control was by going in at the four- to six-leaved stage of the mallow.
“Round-leaved mallow produces leaves very quickly. Between application one and two, there was eight days difference. It’s not a big window, but we were trying to see if it had an impact, and it did, because of the flushing nature of those weeds.”
All the products tested were already registered for use on wheat. They just didn’t have mallow on their labels. All tests were done in wheat, using two different application times: one when the round-leaved mallow was in the one- to three-leaf stage and the other in the four- to six-leaf stage.
“All of the products we were using were applied in the recommended stage of the crop, according to the label. We might have been a little early with the 2,4-D mixes because you’re supposed to wait to the four-leaf stage before applying 2,4-D. All that does is create a bit of knuckling and straw twisting (in the wheat), but we were looking more at weed control,” said Sapsford.
Using the best results from 2002, the trial in 2003 looked at Attain, Prestige, Frontline 2,4-D, Spectrum and Refine Extra plus 2,4-D.
“When we put those on, we got excellent response, both at one- to three- and four- to six-leaf stages, with all five products. Refine by itself is listed for suppression, but we’re mixing it with eight ounces equivalent of 2,4-D ester. It’s a fairly potent mix, but wheat will withstand it without any trouble,” he said.
Sapsford cautioned that these results come from just one site, with only two years of data, so it’s not enough to put round-leaved mallow on the label of any of these products. But usually farmers have a number of weeds in a field that they’re going after.
“With the data we have generated here, even though it’s not on the label, farmers can say, ‘I know I’ve got some mallow, but I’m also going after my buckwheat, Russian thistle,’ or whatever else is in their field. They can see from the work we’ve done at the university, they might get control of their mallow as well, if they use one product instead of another.”
Sapsford said there’s been no herbicide resistance show up in round-leaved mallow populations yet, but Group 2s need watching.
“Attain is a Group 4, and every other one is a combination of Group 2 and Group 4 chemistry. They are compounds that work well to avoid resistance.”
