Balancing economic, action, and seed production thresholds for glyphosate-resistant kochia in canola
Term: 3 years, ending April 2025
Status: Completed
Researchers: Charles Geddes and Prabhath Lokuruge (AAFC); Robert Gulden (University of Manitoba)
SaskCanola Investment: $82,500
Total Project Cost: $165,000
Funding Partners: Western Grains Research Foundation
Project Description
Kochia is a troublesome tumbleweed that is capable of causing substantial crop yield losses. Glyphosate-resistant kochia can be problematic particularly in glyphosate-tolerant crops like canola. New canola cultivars with stacked resistance to glyphosate and glufosinate may offer growers an opportunity to manage kochia plants that survive glyphosate by following up with a rescue application of glufosinate. Understanding when this approach is economically viable could help growers take action quickly and efficiently so that glufosinate may be applied before kochia plants are beyond the window for effective control. A field experiment was conducted to determine the economic and action thresholds for glyphosate-resistant kochia in canola. The nine site-years of research included irrigated locations near Lethbridge, AB, and dryland locations near Lethbridge, AB, Scott, SK, and Carman, MB. The experiment followed a two-way factorial randomized complete block design with four replicates. The factors were canola target density (50 vs. 100 plants per square meter; about 5 vs. 10 plants per square foot) and kochia density (nine seeding rates ranging from 0 to 7290 seeds per square meter). Among site-years, the canola target densities of 50 and 100 plants per square meter resulted in observed plant densities of 53 and 98 plants per square meter, respectively. The 5% action threshold for kochia (kochia density resulting in 5% yield loss) was around 7 kochia plants per square meter. The low economic threshold (yield loss equivalent to $20 per acre) was at 4 kochia plants per square meter, and a high economic threshold (yield loss equivalent to $30 per acre) was at 6 kochia plants per square meter. These thresholds did not change based on whether the canola plants were seeded at a lower or higher target density (50 vs. 100 plants per square meter). However, for some locations, lower canola target densities led to lower kochia thresholds, and in one case, higher densities did. On average, each extra kochia plant per square meter caused about 0.86% yield loss at low densities, but at very high kochia densities, yield loss was about one-third lower when canola was seeded at a higher target density (29.6% vs. 44.1% maximum yield loss at high vs. low canola target densities, respectively). The amount of kochia seeds produced at canola maturity varied widely across sites, from none to nearly 40,000 seeds per square meter. In two out of three locations, higher canola plant densities helped reduce kochia seed production by up to 71%. A 5% kochia seed production threshold occurred at about 13 kochia plants per square meter, with higher target densities showing slightly higher thresholds in some locations. Higher canola plant densities helped it compete better with kochia, reducing yield loss at high kochia densities.
Grower Benefits
Overall, this study suggests that planting canola at higher densities (e.g., 100 target plants per square meter) can improve competition with kochia and reduce yield loss. However, the action and economic thresholds for managing glyphosate-resistant kochia are similar whether canola is seeded at a low or high density. Farmers should take action to control kochia in canola when there are around 4-7 kochia plants per square meter or more.
Objectives
Determine the economic threshold for glyphosate-resistant kochia in canola.
Determine the action threshold for glyphosate-resistant kochia in canola.
Determine whether canola density impacts the economic, action, and seed production thresholds for glyphosate-resistant kochia.
Determine the impact of canola density and kochia density on kochia seed production and return to the soil seedbank.
References
Angadi, S.V., Cutforth, H.W., McConkey, B.G., and Gan, Y. 2003. Yield adjustment by canola grown at different plant populations under semiarid conditions. Crop Science 43:1358-1336.
Geddes, C.M., and Gulden, R.H. 2018. Candidate tools for integrated weed management in soybean at the northern frontier of production. Weed Science 66:662-672.
Mohler, C.L. 2001. Chapter 6: Enhancing the competitive ability of crops. Pages 269-231 in Ecological Management of Agricultural Weeds (eds. M. Liebman, C.L. Mohler & C.P. Staver). Cambridge University Press, Cambridge, UK.
Soltani, N., Geddes, C.M., Tidemann, B.D., Sikkema, P.H. 202Xa. Potential yield loss in canola crops due to weed interference in Canada and the United States. Manuscript in preparation for Weed Technology. Writing stage.