Written by Darrell Deneke, former SDSU Extension IPM Coordinator.
Dandelion has become much more of a problem as farming practices have changed. Less tillage and increased use of glyphosate resistant crops along with reduced use of residual herbicides have allowed some perennial weeds such as dandelion to prevail. The burn down program in row crops is important in keeping dandelion in check. The main goal is to prevent seed production and stopping the emergence of new seedlings. The more mature the dandelion plant is the more difficult it is to control with herbicides.
Established dandelions can be more effectively controlled in the fall than the spring, if conditions are good for fall growth. Work done at SDSU would suggest that adding more glyphosate or 2, 4-D at 1pt/A in the spring and waiting 7 days to plant soybeans can do a good job of controlling dandelion. However, adding a PPO-inhibiting herbicides like Sharpen (saflufenacil), Valor (flumioxazin), or Authority products (sulfentrazone) can increase the speed of desiccation and slightly increase dandelion control. Adding another mode of action to the burn down mix that has foliar plus residual activity helps to reduce the selection of glyphosate resistant weeds. This can also control later emerging dandelions that can become a perennial nuisance in subsequent crops.