Round-Up is a very useful tool when you need to get rid of some unwanted vegetation in areas like sidewalks, driveways, or even fence lines. You just have to be sure to take extreme caution when using it close to vegetation that you don’t want to get rid of. Rain or even your irrigation system can cause round-up to go exactly where you don’t want it to, and in this case, the rain caused some runoff into the actual grass and caused a little damage. Make sure you don’t get too close, and you don’t use too much. If this happens to you, don’t worry too much about it, the grass will eventually fill in over time. Hope this helps, and let us know if you have any questions.