Weedy fields will not only hurt this year’s soybean crop, they will also likely impact crops in that field for many years. The key is to eliminate the threat of weeds early to avoid lost yield and to prevent weeds from maturing and adding to the soil seed bank. Consider these tips to get control of weeds early this growing season:
1. Start clean
Use tillage or a burndown herbicide to make sure fields are weed-free before pulling out the planter. A clean environment will eliminate competition and allow your soybean crop to thrive.
2. Know your weeds
Choose your herbicide based on your worst weeds. Double-check that your chosen mode of action is effective against those troublesome weeds. Be sure to rotate herbicides and use multiple modes of action frequently to prevent weed resistance.
3. Don’t forget the residual
Use a soil-applied pre-emergence herbicide to control weed seeds before they start to grow. Be sure to select a pre-emergence herbicide with residual control to give your soybean crop enough time to grow a canopy and shade out weeds.
4. Weather delays
If the weather prevented you from applying your pre-emergence herbicide before your soybeans emerged, you can still apply a herbicide to keep weeds under control. Identify the growth stage of your soybeans and check to see if it is compatible with your selected herbicide, based on its labeled application window. If not, consult with your local agronomist to discuss alternative herbicides.
(Source – http://unitedsoybean.org/article/tips-for-early-season-weed-control-in-soybeans)