Which of the following factors would have the least effect on the movement of a herbicide from the application site?

Selecting the types of weeds growing on the site in the previous season as the factor with the least effect on the movement of a herbicide is accurate. This is because the previous types of weeds primarily influence the herbicide’s efficacy and necessity rather than its movement in soil or through the air after application. Herbicides are designed to target specific weed species, but their actual mobility is determined more by environmental and physical factors rather than the biological history of the application site.

Soil moisture content plays a significant role in herbicide movement as it affects solubility and absorption, while weather conditions such as wind and rain can greatly enhance or hinder the dispersion and efficacy of an application. Similarly, the equipment used during application can impact how the herbicide is distributed on the surface, influencing both coverage and potential for volatilization or drift. Thus, while knowing the weeds present is crucial for application strategy, it does not affect the physical movement of the herbicide itself.