Marestail, one of the first glyphosate-resistant weeds identified in row crops, is still among the top driver-weeds that can significantly impact your soybean crop each year. With planting kicking off, marestail management should be top of mind.

Marestail is a prolific seed producer; its seeds are light, making them highly mobile and allowing them to rapidly spread by wind to nearby areas. With this weed’s ability to produce 200,000 seeds and grow up to 6’ tall, it’s best to knock it out early and maintain control throughout the growing season.

Start Clean 

Since marestail typically germinates in the fall, a fall or spring burndown application is a key component of achieving the highest level of control early on. If you haven’t already applied your spring burndown, you might still have time. When doing so, it’s important to target any fields with a history of marestail issues.
Along with an effective burndown application, choosing the right pre-emergence herbicide that provides multiple effective sites of action (SOAs) for problem weeds is next on the checklist. Since marestail has become resistant to glyphosate and post-emergence options are very limited, it’s important to select a pre-emergence product that contains SOAs that marestail has not yet developed resistance to. I recommend applying Boundary® 6.5 EC herbicide, containing metribuzin (Group 5) and S-metolachlor (Group 15) for effective marestail management.

Stay Clean – Overlap Residuals 

A common misconception about weed management is that making a single herbicide application is sufficient for keeping fields clean all season. I always recommend overlapping residual herbicides by starting with a pre-emergence application and following up 21 days later with a post-emergence application to prevent weed escapes. Since marestail and several other problem broadleaf weeds have also developed resistance to ALS-inhibitors, I recommend following Boundary with Prefix® herbicide for optimal extended residual control.

Use Full Rates

When making herbicide applications, many choose to only apply partial rates, rather than applying the full rate indicated on the label. Doing so can actually boost the development of resistance to the applied herbicide. I like to make the comparison to an antibiotic treatment for an infection. We’re always advised by our doctors to take the full dosage of the antibiotic even if the infection appears to be gone. This is because if we don’t fully kill the infection, it will come back even stronger and with a resistance to the antibiotic that was used before. The same goes for weeds. Using full herbicide rates will not only be more effective in solving your weed issues, but it will also help prevent weeds from developing new forms of resistance to that herbicide.

The Syngenta Resistance Fighter® program provides education, local recommendations and a comprehensive herbicide portfolio to help growers and retailers effectively manage resistant weeds in their area.

For more information about fighting resistant weeds, visit

Phil Krieg is an Illinois-based agronomy service representative at Syngenta. He educates growers on pests, weeds, disease and other agronomic issues that affect crop production. 

© 2018 Syngenta. Important: Always read and follow label instructions. Some products may not be registered for sale or use in all states or counties. Please check with your local extension service to ensure registration status. Boundary®, Prefix® and Resistance Fighter® are registered trademarks of Syngenta Participations AG

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About the Author: Phil Krieg

Phil Krieg is an Illinois-based agronomy service representative at Syngenta. He educates growers on pests, weeds, disease and other agronomic issues that affect crop production.