When do herbicide liquid sprays more easily penetrate leaf surfaces?

Herbicide liquid sprays are more likely to penetrate leaf surfaces during periods of increasing relative humidity. This is primarily because higher humidity levels can create a more favorable environment for the absorption of the herbicide into plant tissues. When the humidity is elevated, the leaf cuticle, which is the protective outer layer, becomes more pliable and allows for better penetration of the spray.

Additionally, increased humidity can also help to minimize the evaporation of the herbicide solution, ensuring that a greater amount stays on the leaf's surface long enough to be absorbed. Furthermore, high humidity can enhance the effectiveness of many herbicides, as the moisture can facilitate the chemical's action on the target plant.

In contrast, low temperatures often slowdown physiological processes in plants, wind can cause drift and uneven application which reduces efficacy, and high sunlight exposure can lead to quicker evaporation of the herbicide before it has a chance to penetrate the leaf surface. Therefore, increased relative humidity is optimal for herbicide absorption.