Update from the Field: Burn, Baby, Burn!
Posted by Dave Dyson, Agronomist on August 16, 2019
This year’s weed situation has been the worst in my recent memory. I have been called out to many fields where Roundup® and Liberty® are not killing giant ragweed, marestail, waterhemp, or lambsquarter. Some problems can be attributed to a boring insect hollowing out a large weed and not allowing the herbicide to translocate down to the roots (Figure 1).
Figure 1: This picture was taken on July 18, 2019, near Kokomo, Indiana. It shows a European corn borer hollowing out giant ragweed, effectively blocking the herbicide from translocating to the roots.
However, the most common problem is Roundup and Liberty are not working as they did in the past because of a lack of diversity in chemistry, leading to resistance in weed populations. For the remainder of the growing season, the only choice in the toolbox to slow these hardened weeds is a protoporphyrinogen oxidase (PPO) inhibitor such as Cobra® applied at a rate of 10 oz/ac. To be clear, Cobra will not kill weeds. As a PPO, it will burn the weed back and allow the soybeans to outgrow the weed. A PPO may also possibly destroy the weed’s ability to reproduce, though this is not guaranteed.
Cobra is a rescue option, not a planned option, and therefore should be used with caution. Before an application of Cobra, it is essential to be aware that there will be a soybean response and that the top trifoliate will be burnt. To alleviate the burn response that we see following the application of Cobra, we encourage including Phosfix® at a rate of 1-2 pint/acre and OverPass® SF or OverPass SF Plus at a rate of 1-2 gal/acre with the spray solution. The application of Phosfix will help the plant overcome the stress caused by burn, helping the crop grow out of it faster. The addition of OverPass SF or OverPass SF Plus will provide the crop adequate nutrition, allowing the plant to focus its energy on healing rather than nutrient scavenging.
In conclusion, talk to your Ag Advisor about using Cobra at 10 oz/ac to burn back hardened weeds that Liberty and Roundup cannot control. To lessen the burning effect and speed up the recovery time on soybeans, add Phosfix and OverPass SF or OverPass SF Plus to the spray solution. If all else fails, talk to your Ag Advisor about applying Gramoxone® as a harvest aid.
Take Away Bullets:
- Resistant weed problems are present everywhere this year
- Add Cobra at 10 oz/ac to reduce weed pressure
- Apply Phosfix 1-2 pt/ac and OverPass SF or OverPass SF Plus for the remainder of the season
- Contact your local Ag Advisor for more information
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Dave Dyson is a regional agronomist for The Andersons’ Farm Centers which are located throughout Ohio, Michigan, and Indiana. He is an Indiana native and grew up on a dairy farm in Miami County. A graduate of Purdue University with a degree in Crop & Soil Science, Dave has a deep knowledge of various agronomic topics and is committed to helping growers improve their crops. If you have any questions, Dave can be reached at david_dyson@andersonsinc.com.
Phosfix and OverPass are registered trademarks of The Andersons, Inc. Roundup is a registered trademark of Monsanto Technology LLC. Liberty is a registered trademark of BASF. Gramoxone is a registered trademark of Syngenta. Cobra is a registered trademark of Valent U.S.A. LLC.
