What happens to the efficacy of herbicides as plants reach maturity?

The efficacy of herbicides generally decreases and becomes less practical as plants reach maturity. This is largely due to the physiological changes that occur in mature plants. As plants grow, they can develop thicker cuticles, deeper root systems, and greater overall biomass, all of which can contribute to a reduced uptake of herbicides. Mature plants may also have a more extensive system of protective mechanisms that can break down or detoxify herbicides, making them less susceptible to chemical control.

Additionally, mature plants are often more established and can outcompete herbicides through their growth and photosynthetic capacity. This means that the likelihood of effective control, particularly of perennial weeds, decreases as the plant matures. Consequently, it can become more challenging to manage these plants with herbicides once they have reached full maturity, leading to less practical and fewer successful applications.

The increase or unchanged efficacy scenarios do not account for these biological and chemical processes that affect herbicide performance, while the dependency on the type of herbicide does not fully capture the broader impacts of plant maturity on herbicide effectiveness.