Which of the following is a characteristic of non-residual herbicides?

Non-residual herbicides are designed to break down quickly in the environment and do not persist in the soil for extended periods. This characteristic leads to a need for more frequent applications to maintain effective weed control throughout the growing season. These herbicides are typically used when the target weeds are actively growing and are often applied shortly after weeds emerge, as they do not offer long-term effects.

The other choices point to characteristics that are not aligned with non-residual herbicides. For instance, lasting several months in the soil refers to residual herbicides, which maintain their activity over time. Requiring less frequent applications suggests longer-lasting effects, also indicative of residual herbicides. Effectiveness after weed emergence indicates that these herbicides typically target weeds once they are visible, aligning with non-residual herbicides but in conjunction with the requirement for more frequent applications due to their short-term nature.