Soybean development and yield can be affected by weeds right from the start. Developing soybeans are heavily influenced by what’s going on around them and can sense the presence of weeds even before they’re emerged.
Use a two-pass weed control system. First, keep soybean fields weed free until V3 to protect yield and improve in-crop weed control. Then, if needed, use an in-crop application to control weed escapes and late emerging weeds.
What the Research Says
Keep’em weed free until V3 - Allison Hayward, Ph.D.
The benefits of starting soybeans clean and keeping them clean are two fold:
- Prevent early season yield losses from weed competition (the critical weed-free period)
- Make in-season weed control more flexible and complete
Young developing soybeans are heavily influenced by what’s going on around them. Research conducted by Dr. Clarence Swanton with the University of Guelph shows that soybeans sense the presence of weeds even before they are emerged. Newly emerged soybeans respond to weeds by altering their growth, such as decreasing root size and nodulation. This means that right from the very beginning, soybean development and most importantly yield are reduced if any weeds are present. It also must be kept in mind that yield cannot be recovered, so it’s extremely important to prevent weeds from even emerging during the early stages of soybean production.
Keeping soybean fields weed free until V3 does more than protect yield, it improves in-crop weed control. If an in-crop herbicide application is needed (to control any escapes and late geminating weeds) the size and abundance of the weeds will be significantly reduced from a PRE herbicide application. This will improve the effectiveness of the in-crop herbicide. Though yield reduction from weeds emerging after V3 is minimal, removing late germinating weeds benefits harvest efficiency, bean quality and reduces the number of weed seeds returning to the soil.
RealAgriculture.com. 2016. Soybean school: Starting clean more critical than ever. Interview with Clarence Swanton and Peter Johnson.
Gal, J., Afifi, M., Lee, E., Lukens, L., and Swanton, C. 2015. Detection of neighboring weeds alters soybean seedling roots and nodulation. Weed Science. 63: 888-900
1. Personal communication with Dr. Peter Sikkema.