Lack of rain following soil-application of herbicides may allow weeds to grow and germinate ____ the herbicide moves into the soil solution.

The correct answer highlights the relationship between soil application of herbicides and the subsequent environmental conditions that affect weed germination. When herbicides are applied to the soil, they need sufficient moisture, typically from rainfall, to dissolve and be taken up by the plants. If there is a lack of rain following the application, weeds can germinate before the herbicide has effectively moved into the soil solution.

In this case, the term 'before' accurately encapsulates the timing of the germination process relative to herbicide activation. Without adequate moisture from rainfall, the herbicide may not penetrate the soil effectively, leading to a situation where weeds may sprout prior to the herbicide being activated or becoming effective in controlling them.

This concept underscores the importance of considering environmental factors when applying herbicides; a dry period following application can lead to inconsistencies in weed control, allowing the weeds to establish themselves unhindered while the herbicide remains inactive in the soil.