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Understanding cleavers populations in Western Canada

Developing strategies and tactics to improve cleavers management.

February 20, 2024  By Donna Fleury


Seeds from all populations of cleavers were seeded in plots both in early spring, and at the end of July/early August at all three study locations. PhotoS courtesy of Breanne Tidemann, AAFC Lacombe, Alta.

Cleavers is a problem weed for many growers and can be particularly challenging for growers in the Black soil zone areas in central and northern Alberta and Saskatchewan. Cleavers is a serious contaminant of canola, with a similar seed size and shape, causing harvest difficulties and lowering seed quality. To better manage cleavers, researchers are investigating various populations to find out what factors affect their growth under different environmental conditions and in different locations.

 “Cleavers are a very prominent weed on the Prairies, with increasing abundance in many of the provincial weed surveys over the past several years,” says Breanne Tidemann, research scientist with Agriculture Agri-Food Canada (AAFC) in Lacombe, Alta. “There are two species of cleavers that grow on the Prairies: Galium aparine (cleavers) and Galium spurium or false cleavers, which have similar growth patterns and are difficult to distinguish. Cleavers can be quite variable, and we are interested in what factors are causing that variability, such as the timing of emergence, seed production or location and environmental conditions. The goal of the project is to increase our understanding of cleavers biology and cleavers populations in Western Canada and use this knowledge to better inform management strategies.” 

Tidemann initiated a project in 2021 in collaboration with AAFC research scientists Charles Geddes in Lethbridge and Shaun Sharpe in Saskatoon to evaluate cleavers populations from across the prairies to determine what is driving some of the differences between biotypes. Chris Willenborg, research scientist at the University of Saskatchewan (USask), has also provided some insights on the recent work his graduate student Andrea De Roo did on cleavers. 

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“For the project, we collected cleavers seed from across Western Canada and then grew the same seeds in three locations: Lacombe, Lethbridge and Saskatoon,” explains Tidemann. “We wanted to evaluate the differences and determine whether it was the location and environment they were growing in that was driving differences or was it more about the location where the seed originated. By growing the mixed populations in three different locations, we hoped to find out more about the biology and factors affecting the variability. Information such as emergence phenology, whorl/branch number, flowering, seed production, seed weight and over-wintering ability are being measured.”

 In the first year, researchers collected seeds from producer fields in Alberta, Saskatchewan and Manitoba. Due to drier conditions, cleavers were less abundant, and researchers ended up with 25 populations, including 12 from Alberta, eight from Saskatchewan and five from Manitoba. In the first field season, seeds from all populations were seeded in plots both in early spring and at the end of July/early August at all three locations. One very noticeable difference came from that fall seeding.

 “In the fall, Lacombe had fall-emerging cleavers pretty well established, and most survived over the winter,” says Tidemann. “In Lethbridge, the plots had fall-emerging cleavers, but they all died overwinter, and in Saskatoon, no cleavers emerged in the fall. In 2023, the dry conditions didn’t result in significant cleavers populations in producer fields, and lower densities than in 2022 in the plots. However, all locations had fall-emerging cleavers, with Saskatoon and Lacombe seeing hundreds of seedlings emerge in a week after receiving precipitation. This demonstrates that cleavers are very moisture responsive.”

Estimating cleavers seeding emergence in the plots.

Tidemann notes that for growers in a cleavers-dominant area like the Black soil zone, watching for seedling emergence after rainfall will be important. Similar to wild oat seedling flushes, cleavers does the same thing, although it has not been something that has been focused on in terms of cleavers management. Therefore, in a wet year, scouting and controlling cleavers in their lifecycle will be important. Group 2 resistance is increasing, with the 2017 weed survey in Alberta showing 40 per cent of cleavers resistant to Group 2 and in the most recent survey in Saskatchewan, 40 per cent of cleavers were resistant to Group 2.

 “When considering an integrated weed management strategy, cleavers respond differently and don’t seem to be as susceptible as wild oats to tactics for cultural control,” explains Tidemann. “Cleavers are a bit trickier to manage than wild oats because of their biology. With wild oats, increasing seeding rates or growing winter cereals can be a good management strategy. However, cleavers don’t seem to be as responsive. Cleavers can climb up the crop and therefore don’t suffer the same reduction that a wild oat might from increased seeding rates. Winter cereals can be very competitive to wild oat, which generally emerges in the spring. However, because cleavers emerges both in the fall and spring, it is more competitive in winter cereals than wild oat. Cleavers that overwinter can get a jumpstart on the crop and are sometimes too large to be effectively managed with a pre-seed burnoff.”

 One additional component of the project that is still underway is a baseline screening for quinclorac resistance and a very preliminary assessment of the frequency of resistance. In the mid-90s, a population of quinclorac-resistant cleavers was identified in Alberta, and recently, there are increasing applications of quinclorac on cleavers, particularly in glufosinate canola. In the initial screening, some of the cleavers population continued to flourish after spraying with quinclorac. But after additional testing, resistance was not confirmed in those biotypes.

 However, there is some reason those populations are not dying in the field, and it’s not clear if it is related to drier spring conditions or drought stress that is making them less susceptible, or something else that is going on. For now, growers should monitor closely, particularly if it’s a dry season and quinclorac is being used. Make sure to scout the field afterward to see if the cleavers have been controlled. Knowing that resistant biotypes were confirmed at one time, managing cleavers to minimize selection pressure is important to continue to reduce the risk of resistance. 

The project will wrap up in 2024, with data collected on overwintering cleavers populations. After that, the large data analysis and final results of the project will be completed and made available.

 “In a side-project, Sara Martin, with AAFC in Ottawa, is leading mapping of the cleavers genome,” adds Tidemann. “We were able to share the populations we collected from Alberta and Saskatchewan; unfortunately, we didn’t have the Manitoba collection in time. Dr. Martin’s analysis showed that all of the seeds she tested were G. spurium or false cleavers, which agrees with the USask research that Andrea had done. We are hoping this research together with our results will help us understand the differences we are seeing in the populations and help develop strategies and tactics to improve cleavers management.” 

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