Reporting
Sunflowers do well in prairie

Sunflowers do well in prairie fields in years that perennial weeds do not. In a sense, they are both competitors and also complement each other.
Here is a good page on preparing a field for sunflowers: http://mdc.mo.gov/your-property/wildlife-your-property/wildlife-food-plots/sunflowers-wildlife
Keep in mind that pre-plant herbicides affect other prairie species.