Competition

• Sunflower yields compete with weeds for nutrients, moisture, and sunlight. Annual weeds pose a higher risk than perennial weeds in terms of competition. To prevent annual weeds, apply a pre-emergent herbicide to the sunflower soil. Pre-emergent herbicides are herbicides applied before the sunflower begins to sprout.
  
  

Soil Condition

• Soil condition is an important factor when using any herbicide intended to control weeds around sunflowers. The soil cannot be wet or full of clods during the preplant herbicide application. Wet soil or clod soil will prohibit the herbicide from properly mixing in, limiting its effectiveness. Early tillage of the soil with a rotary hoe will kill weeds. Tillage should take place about one week after the sunflower seeds have been planted.
  
  

Warning

• Those looking to control weeds in sunflowers may assume they can use any herbicide on the market. However, federal law prohibits using herbicides on sunflowers unless that herbicide is specifically designed for sunflowers.