Which condition promotes thicker cuticle formation and reduces herbicide absorption?

High temperatures promote thicker cuticle formation in plants, which serves as a protective barrier against various environmental factors. The cuticle is a waxy layer covering the plant's surface that helps to prevent water loss and, importantly, reduces the absorption of herbicides. When temperatures rise, plants may respond by increasing the production of cuticular waxes, thereby enhancing the thickness and effectiveness of this protective layer. This thicker cuticle can fortify the plant against the penetration of chemicals, including herbicides, limiting their effectiveness.

In contrast, other factors like low soil moisture or increased humidity generally do not contribute to increased cuticle thickness. Low soil moisture can lead to stress in plants but may not directly induce cuticle thickening as a response. Increased humidity often supports more efficient transpiration and can sometimes help reduce stress, potentially resulting in thinner cuticles as the plant does not need to conserve water as aggressively. High soil pH can affect nutrient availability and plant health but does not have a direct relationship with cuticle thickness.