Marestail or horseweed (Erigeron canadensis) is a challenging weed to manage in no-till or minimum-till soybeans systems. This weed is classified as a winter annual, but it germinates well into spring and summer, making it even more difficult to manage. In addition to an extended germination window, marestail can produce up to 200,000 seeds/plant, with approximately 80% of those seeds being able to germinate immediately after maturation. Kansas producers also face the added difficulty of trying to manage glyphosate-resistant marestail.
Acceptable control of fall-emerged marestail with herbicide applications at planting will be unlikely because the marestail are generally too large, but control can be achieved with both fall and early spring herbicide applications. Other control options include tillage and cover crops.
Residual herbicides for marestail control include chlorimuron (Classic, others), flumioxazin (Valor, others), sulfentrazone (Spartan, others), and metribuzin products. Group 4 herbicides such as 2,4-D, dicamba, fluroxypyr (Starane Ultra), or haluxifen (Elevore) are good options to control emerged marestail, especially populations that are resistant to glyphosate or ALS-inhibiting herbicides. Control of marestail in the rosette stage is similar among the Group 4 herbicides, but dicamba controls bolted marestail better than 2,4-D. Saflufenacil (Sharpen) or glufosinate (Liberty, others) applied can also control bolted marestail.
Fall and spring tillage has been shown to be effective in controlling marestail for a spring-planted crop. When tillage is not utilized in the fall, marestail will establish and be present in the spring. If implementing a minimum tillage system is the goal, marestail can be controlled when a fall herbicide application is followed by shallow tillage in the spring or vice versa.
Cover Crops -utilizing cover crops can result in fewer and smaller marestail plants in a field. Recent research in Kansas has shown control of marestail with a cereal rye cover crop paired with spring herbicide applications. The key to effectively suppressing marestail with cover crops is the accumulation of adequate cover crop biomass before marestail emerges, so timely cover crop planting is important for this strategy to succeed.
For additional information, see the “2023 Chemical Weed Control for Field Crops, Pastures, and Noncropland” guide available online. Just type into your internet browser “Chemical Weed Control Guide, KSU”. Or check with your local K-State Research and Extension office for a paper copy.
The use of trade names is for clarity to readers and does not imply endorsement of a particular product, nor does exclusion imply non-approval. Always consult the herbicide label for the most current use requirements.
Stacy Campbell is an Agriculture and Natural Resources agent for Cottonwood Extension District. Email him at scampbel@ksu.edu or call the Hays office, 785-628-9430.
