With broadleaf products especially, I don't like to spray when there is too much dew or high temps, particularly coupled with low humidity in the later case. No matter whether you are using ester, low ester or amine formulations, the stuff still fumes to some extent. That's why you can smell it when driving past a sprayed field. When the temps get high, the stomata cells on the underside of the leaves close, to conserve moisture. These are the cells that the leaves breathe through. How much they close depends on the humidity. If the chemical enters through the stomata cells, intake is rapid and goes straight into the circulation system. Yes, it is also adsorbed through the cutin (waxy) layer protecting the top leaf surface. Surfactant is added to the spray mix to both break down the water droplets and produce a fine film on the leaf and to aid in adsorption. Adsorb is to translocate through a surface, absorb is....well, absorbed BY the surface. And living leaves don't absorb.
Got sidetracked there a little. Sorry. I hold off spraying in either of these conditions. If just a little dew, I will spray. Spraying in the late afternoon, early evening can be the best there is. Winds tend to be calm, humidity is rising, so the stomas are opening and it can have several hours to dry and be adsorbed before the heavy dew sets in.
