When are herbicides most effective for controlling woody plants?

Herbicides are most effective for controlling woody plants when applied to small plants. This is because younger, smaller plants have a more active growth stage, which allows them to absorb herbicides more effectively. Smaller plants generally have a less extensive root system and lower biomass, making them more susceptible to the action of herbicides. They also tend to have less developed protective mechanisms that can resist the chemicals, resulting in a higher likelihood of effective control.

In contrast, applying herbicides to mature trees can often be less successful due to their larger size, thicker bark, and robust root systems, which can act as barriers to the uptake of the herbicide. Additionally, larger plants may have already developed resistance mechanisms over time.

Applying herbicides to flowering plants may not necessarily target the control of woody plants effectively since the flowering stage doesn't correlate with the vulnerability to herbicides. The timing and the plant's physiological state are critical factors for effective control.

Using herbicides in dry conditions might limit their effectiveness as well, since dry environments can reduce the herbicide's absorption and translocation in plant tissues. For optimal control, conditions that promote herbicide uptake and action are ideal, which is typically found in the context of smaller and actively growing plants.