Hi, 

This is Japanese Stilt Grass. You can review our tips for managing it on the link provided. There are additional links at the bottom of the page and, the one for Penn State is helpful as well. 

At this point in the season, you can hand dig up the large clumps, use a targeted post emergent spray on the areas of it, or keep mowing it with your lawn until the fall. Then in the fall as it starts to go to seed, you can make sure to bag your lawn clippings and dispose of them. If you mow those areas lower than the rest of the lawn you can try to limit the offput of having them go to seed again. The following spring, you can apply a granular pre-emergent to help prevent new plants from germinating. 

Let us know if you have specific questions with the information on the link and we can help direct you further. 

Emily 

The photos you are showing us does look like Japanese stilt grass to us. Mowing it and the different ages of the grass, even sun and shade patterns, can change the look of the leaves and growth patterns. 

When and how are you applying the herbicide? Are you following all the label directions? Plants can change and develop resistance to chemicals so that could be happening but we are not aware of it with that chemical yet. 

The roots could depend on soil type and age of the plant as well. 

If you think it is something different we would need to be able to see some other grass identification characteristics like the ligule, oracle, flowers and seed heads, etc. The link we provided is a key to ID grass from Virginia Tech. 

Emily

you're welcome- happy to help further if we can!