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Expanding chickpea weed control options

Research looked at a new herbicide active ingredient to improve weed control.

March 10, 2024  By Bruce Barker


U of S research investigated new weed control options in chickpea. Photo by Bruce Barker.

With funding from the Saskatchewan Pulse Growers, researchers at the University of Saskatchewan Plant Sciences Department are looking at how to improve weed control in chickpeas. Three recently completed studies looked at a new herbicide active ingredient in chickpeas and examined the crop safety of registered herbicides to gain a better understanding of how to improve weed control.

“Several cases of herbicide resistance pose a threat to pulse crop production, including Group 2-resistant cleavers, wild mustard, and hemp-nettle, and Group 9-resistant kochia,” says Chris Willenborg, professor and Plant Sciences Department head. The U of S research, led by Willenborg, sought to address these herbicide resistance challenges and to expand weed control options in chickpeas. It focused on two main topics. The first was whether the Group 6 active ingredient pyridate was safe to use on chickpeas and if it was effective on kochia. The second looked at chickpea variety tolerance to pre- and post-emergent herbicides.

A new chickpea herbicide
Pyridate is a Group 6 broadleaf herbicide that has been used in horticultural crops for many years. Willenborg says it was previously evaluated as a potential herbicide for chickpeas at both Scott, Sask., and the University of Saskatchewan. At that time, crop tolerance was very good, but Syngenta did not move ahead with registration. A few years ago, Belchim Crop Protection bought the product and was interested in pursuing registration.

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Willenborg investigated chickpea tolerance to pyridate in 2019 and 2020 to revive the potential of this new chickpea herbicide. In 2019 at the U of S Kernen Research Farm, the trial included a hand-weeded untreated check, pyridate (1x rate; 900 g ai/ha), and pyridate (2X rate; 1,800 g ai/ha). Sencor 75DF herbicide was also included as an industry standard. Application was made at the two- to three-node stage.

In 2019, chickpea had good tolerance to both the 1x and 2x rates of pyridate. The visual injury ratings were consistently lower than the maximum acceptable level of crop injury of 10 per cent and also lower than the industry standard Sencor. No significant difference in yield was found between the pyridate treatments and the hand-weeded check.

Willenborg also conducted a weed control study looking at pyridate’s effectiveness on kochia. With the confirmation of Group 2, 4, and 9 herbicide-resistant kochia, an alternative herbicide group for kochia control would be a valuable tool. The trial was carried out at Kernen Research Farm from 2018 to 2020. Treatments included a weedy check, pyridate, Sencor and a tank mix of both applied post-emergent at different rates. All herbicide treatments were applied when kochia height was between 0.4 to 1.6 inches (one to four centimetres) tall, and some treatments also included a sequential application when kochia was two to four inches (five to 10 cm) tall. There were 12 different herbicide treatments in total.

At the final rating date 56 days after treatment, three treatments provided greater than 82 per cent kochia control, although none reached 90 per cent. The first was an early application of pyridate (300 g ai/ha) + Sencor (101 g ai/ha) followed by a late application of pyridate at (600 g ai/ha). The second treatment to achieve commercially acceptable control was with early and late sequential applications of pyridate (300 g ai/ha) + Sencor (101 g ai/ha).

The third treatment was an early application of Sencor (200 g ai/ha) followed by a late application of pyridate (900 g ai/ha).

“In general, chickpea has exhibited excellent tolerance to pyridate. The current herbicide combinations used in this study provided promising activity on kochia; however, testing and finding a more efficacious tank-mix partner would give chickpea growers more herbicide weed control options to rotate to and thus, better kochia herbicide-resistant management,” says Willenborg.

Pyridate has since been registered as Tough 600EC. In chickpeas, it has been registered for pre- and post-emergent control of black nightshade, redroot pigweed, kochia, lamb’s quarters, false cleavers and wild mustard.

Investigating the chickpea health issue
A third study looked into undiagnosed chickpea health issues in southern Saskatchewan that began in 2019. Chickpea variety and herbicide residue interactions were thought to be potential reasons for poorly performing chickpeas. To investigate this theory, Willenborg screened eight imi-tolerant chickpea varieties, both kabuli and desi types, for differences in herbicide tolerance for both pre- and post-emergence herbicides. The trials took place at the U of S Kernen and Goodale sites.

The three herbicide treatments tested were sulfentrazone (Authority) applied pre-emergent, metribuzin (Sencor) post-emergent and Authority pre-emergent + Sencor post-emergent. The treatments also included a hand-weeded, untreated check. Sencor was applied at the two-node stage of chickpeas.

Varieties compared were CDC Leader, CDC Orion, CDC Lancer, CDC Orkney, CDC Pasqua, CDC Consul and CDC Kala.

Data collection included the date of emergence, crop counts, visual ratings of crop phytotoxicity, crop yield and thousand kernel weight.

There were no differences between varieties for crop phytotoxicity or crop yield in response to the different herbicide treatments. However, there were some differences in crop phytotoxicity depending on the herbicide treatment.

At 14 days after treatment, applying Authority alone had similar crop injury as the untreated control – 0 phytotoxicity. Sencor applied post-emergent had an injury rating slightly less than the 10 per cent tolerance level and was significantly higher than the control and Authority application. The Authority + Sencor sequential application had significantly the highest injury at 13 per cent.

Results of the ratings taken at 25 days application varied between sites. At the Kernen site, all herbicide treatments had less than 10 per cent phytotoxicity. At the Goodale site, Sencor alone and the Authority + Sencor treatments were statistically similar with a toxicity rating greater than 10 per cent.

Willenborg says this may be indicative of problematic tolerance to these herbicides on sandier soils with lower organic matter. Authority alone was statistically similar to the control. 

Despite higher toxicity ratings for the Authority + Sencor application, this treatment produced the statistically highest yield. This was likely due to improved weed control both before and after crop emergence. Authority alone and Sencor alone also had statistically higher yields than the control. This is likely because despite hand weeding, some competition from weeds still impacted yield.

Chickpea health issues were not observed in this trial, so whether herbicide tolerance was a contributing factor is inconclusive. 

Overall, the three research trials provide more insight into weed management in chickpeas. The active ingredient pyridate can provide commercially acceptable control, marginally better than 80 per cent, when used in combination with Sencor in a sequential application. And while layering Authority and Sencor sequentially produced higher crop injury, crop yield was 35 per cent higher than when either product was applied alone. 

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