Forest Pest Control Category 2 Practice Test

The effectiveness of TSI (Timber Stand Improvement) herbicides is influenced by the biological activity of plants, which varies by season. During the spring, many plants, especially undesirable ones, are actively growing and are in a phase known as "spring flush," where they are vigorously photosynthesizing and transporting nutrients. This active growth phase means that the plants can metabolize herbicides more efficiently, leading to greater tolerance and survival despite herbicide application. Therefore, TSI herbicides tend to be least effective during this time due to the plants' ability to resist the chemical effects.

In contrast, winter is a period of dormancy for most woody plants. During this time, plants are not actively growing, which reduces their metabolic activity and makes them more susceptible to herbicide effects. Summer and fall, while showing varying growth rates depending on species, generally offer better conditions for herbicides compared to spring, as many plant species have completed their growth cycle by fall, and competition among plants reduces, making herbicides more impactful in controlling undesirable species.