Certified Professional Horticulturist (CPH) Practice Exam

Which herbicide must be applied before weed seeds germinate?

1. Pre-emergent

2. Post-emergent

3. Soil sterilant

4. Emulsion

The correct answer is: Pre-emergent

The correct choice is pre-emergent herbicides because they are specifically designed to be applied to the soil prior to the germination of weed seeds. Their function is to create a barrier or to inhibit the growth of weeds at an early stage, effectively preventing them from emerging in the first place. Pre-emergent herbicides work by interfering with the biological processes involved in seed germination and early establishment, which means that they need to be applied before weeds actually sprout. In contrast, post-emergent herbicides are formulated to target and kill weeds that have already emerged and established above the soil surface. Soil sterilants go a step further by not only controlling weeds but also eliminating all plant life in treated areas, and emulsions are a type of formulation often used for mixing herbicides rather than defining the timing of application. Understanding the timing and mechanism of these different types of herbicides is crucial for effective weed management in horticultural practice.