Shirtliffe: Can harvest weed seed management be used to control kochia, cleavers and wild buckwheat?
Date: April 2017
Term: 3 years
Status: Completed
Researcher(s): Steve Shirtliffe, Lena Syrovy and Shaun Campbell, University of Saskatchewan
SaskCanola Investment: n/a
Total Project Cost: n/a
Funding Partners: n/a
Project Summary
In recent years herbicide resistant weeds have become increasingly problematic in canola, and weed densities have increased approximately three-fold in comparison to 2003 surveys. In a three-year study, researchers evaluated the potential of harvest weed seed management techniques to manage seed production of cleavers, kochia, and wild buckwheat in canola. The results showed that seed shed of these three weeds can be predicted based on growing degree days, and that harvesting as early as possible, with the use of chaff collection or pulverization techniques, will minimize the number of seeds returned to the weed seed bank. The results also showed that pre-harvest herbicide application did not reduce the number of seeds shed by harvest time nor reduce weed seed viability. Therefore, farmers could save time and money by avoiding pre-harvest herbicide application, and focus instead on timely harvest to prevent problematic weeds from spreading seeds in their fields.
In recent years herbicide resistant weeds have become increasingly problematic in canola. Weed density has increased approximately three-fold in comparison with the survey in 2003 and is now higher than weed densities in the 80’s and 90’s. Weed populations in canola are now higher partially because weeds and weed communities have either evolved to either select for difficult to control species, or those that are completely resistant to the herbicide system. Recently, harvest weed seed management, such as chaff collection, seed destruction and narrow harvest windrow burning, has emerged as a strategy to manage herbicide resistant and hard to kill weeds.
Researchers at the University of Saskatchewan conducted a three-year study to evaluate the potential of harvest weed seed management techniques to manage seed production of cleavers, kochia, and wild buckwheat in canola. Two experiments were conducted in 2014, 2015, and 2016 in central Saskatchewan, with the main objectives to determine the timing of seed shed in cleavers, kochia, and wild buckwheat growing in canola, and to assess the efficacy of pre-harvest herbicides in reducing viable weed seed production in these three weed species.
In the timing of seed shed trials, both naturally occurring weed populations and trials with transplanted weeds were sampled. Catch trays for cleavers and wild buckwheat, or mesh bags for kochia were set up to capture seeds falling off weeds and emptied weekly. At the end of the each experiment at each site, the sampled plants were collected, and remaining seeds were threshed off the plants, weighed and quantified to determine the proportion of total seeds produced that were shed by plants on each sampling date.
The study results showed that seed shed of cleavers, kochia, and wild buckwheat can be predicted based on growing degree days (GDD). Natural populations of cleavers and wild buckwheat required fewer growing degree days than kochia to shed 10 per cent of seeds produced on the plants. Seed shed of cleavers and wild buckwheat began at approximately 1390 GDD, which coincided with the last week of August in 2015, and the third week of August in 2016. Kochia seed shed began at approximately 1585 GDD, which coincided with the last week of September in 2015, and the second week of September in 2016. However, over the course of the experiment kochia shed a much larger number of seeds than cleavers and wild buckwheat, averaging nearly 3500 seeds, compared with 194 and 152 for cleavers and wild buckwheat, respectively. These results highlight that harvesting as early as possible, with the use of chaff collection or pulverization techniques, will minimize the number of seeds returned to the weed seed bank. Early planting and/or growing early maturing varieties may aid producers in collecting more weed seeds at harvest.
In the second pre-harvest herbicide study, the efficacy of diquat and glyphosate in reducing weed seed production and viability compared with untreated control was assessed. Weed seeds were collected from catch trays (cleavers, wild buckwheat) or mesh bags (kochia) prior to (pre-) and 10-14 days following (post-) herbicide treatment. The experiment was conducted in both natural and transplanted weed populations.
The results showed that pre-harvest herbicide application did not reduce the number of seeds shed by harvest time for cleavers, kochia, nor wild buckwheat. Pre-harvest herbicide treatment efficacy did not differ between natural and transplanted sites.
This suggests that pre-harvest herbicide application is not early enough to prevent seed formation, nor reduce weed seed viability for the three weed species tested. To the contrary, there appeared to be some evidence that pre-harvest herbicides encouraged shattering of mature weed seeds compared with direct harvesting. Therefore, farmers could save time and money by avoiding pre-harvest herbicide application, and focus instead on timely harvest to prevent problematic weeds from spreading seeds in their fields.