If the hairs prevent the spray droplets from contacting the cuticle, uptake is reduced. If the hairs help intercept and retain more droplets, they can increase herbicide penetration. Air and soil temperatures also affect the rate at which the herbicide diffuses through the cuticle or root surface. Optimum temperatures for plant growth will also be optimum for diffusion. Under high temperatures, the herbicide droplet can dry before the active ingredient has entered the weed.
High humidity can aid herbicide diffusion because the droplet dries more slowly.
Plants under water stress close their breathing pores to conserve internal moisture supplies. This action slows herbicide entry. Once the herbicide is absorbed, it must move to the site of action inside the plant. Food production, or photosynthesis, occurs in the presence of adequate light and moisture. Therefore, herbicide translocations within the plant will be slowed if the weed is shaded or under high water stress.