What effect do cool and cloudy weather conditions following the application of foliar herbicides have on their effectiveness?

Cool and cloudy weather conditions following the application of foliar herbicides can reduce their effectiveness primarily for a couple of key reasons related to the herbicides' absorption and translocation processes. Herbicides generally require a certain range of temperature and light exposure for optimal activation and absorption by the target plants.

In cooler temperatures, plant metabolism and physiological processes slow down, which can hinder the absorption of herbicides. When the foliage is cool, the stomata of the leaves may be less open, reducing the uptake of the chemical. Additionally, cloudy weather can also limit the amount of light available that is necessary for certain herbicides to function effectively, as light can play a role in enhancing the uptake and activity of these chemicals.

Furthermore, if rain occurs shortly afterapplication, particularly in cool conditions, it may wash off the herbicide before it has a chance to penetrate and be absorbed adequately, further diminishing its effectiveness. Therefore, the combination of lower temperatures and reduced light conditions can lead to a significant decrease in the efficacy of foliar herbicides.