Weeds compete with crops for space, nutrients, and sunlight and left unchecked can make it impossible to grow a crop.  Consequently, over 90% of US cropland is treated with herbicides.  The alternative to herbicides is cultivation which increases fuel and labor costs and increases soil erosion. In fact, no-till farming, a practice that is utilized to decrease soil erosion, is only possible with herbicide use.  In spite of the widespread use of herbicides, the quantities of herbicide applied to US cropland has been decreasing since the late 1990s largely due to the use of herbicides that are effective at much lower rates than older chemistries.