Tips for Controlling Glyphosate-Resistant Common Ragweed

Common ragweed (Ambrosia artemisiifolia) (Figure 1) can be a difficult-to-control weed in corn and soybean systems for several reasons:

• It is one of the earliest emerging weeds in corn and soybean.
• It begins germinating in May and continues to emerge through early June.
• Resistance to glyphosate herbicides.

Management strategies to help control glyphosate-resistant common ragweed populations include:

• Start with a burndown. To control early emerging common ragweed, use a tank mix of Roundup PowerMAX^® herbicide in combination with dicamba or 2,4-D and a residual herbicide or tillage. Starting clean is an effective way to maximize season-long weed control.
• Timely postemergent applications. Weeds are more effectively managed when they are less than 4 inches tall. Tank-mix partners should include those that are labeled for common ragweed control.
• Additional POST application. Plan for a two-pass POST application to control late-emerging weeds, especially where weed populations are dense, and consider using a different mode-of-action herbicide.
• Crop rotation/cultural practices. Ragweed species can be more difficult to control in soybean rotations; therefore, in some cases, the most effective strategy may be to rotate to corn to take advantage of more effective herbicides.

Although these best management practices can help with the control of glyphosate-resistant common ragweed, it is best to proactively manage weed populations to prevent resistance. This can be achieved by:

• Using herbicides with residual activity that have multiple modes of action.
• Always applying herbicides at full rates to reduce the opportunity for weed escapes.
• Starting clean and staying clean.
• Controlling weeds when they are 4 inches or less when they are easier to control.
• Using glyphosate responsibly. Glyphosate should always be applied at the correct rate when weeds are small. It is important to utilize tank-mix partners with varying modes of action in combination with PRE and POST programs.
• Scouting fields for weed escapes. If any are found, they should be mechanically or chemically removed.
• Crop rotation. This allows for different weed management options as well as different cultural practices.

Being proactive can help minimize the risk of developing weed resistance on your farm. For more information on weed management by crop and geography, including practices to help improve the control of tough-to-manage glyphosate-resistant weeds, visit www.RoundupReadyPLUS.com.