Has your garden plot ever looked like this? Of course not, I rarely ever see this when I'm mowing...
If you ever find yourself in this situation, you will have a lot more success killing the weeds if you spray them first, and then knock them down with the string trimmer. The more surface area of the plant you can get the herbicide on, the more will be absorbed, and the better chances of killing the plant completely. I often see people knock the weeds down first, and then spray. By then all that's left are the stumps that are buried below cut foliage, and it is difficult to get the herbicide to where it will have the most effect. Soon the weeds will be right back to where they were before. Spraying beforehand will also kill and dry out the weeds, which makes them easier to cut down. If that doesn't work you can always get one of these.
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