A new type of fine grass is showing up in my lawn, mainly where the lawn meets the sidewalk. It's very fine, grows from a central spot and grows much faster than the rest of the grass. What is it? Is it invasive, like I think it is?
This is not an invasive grass. The fine blades suggest that it is one of the fine fescues. Your other grass is probably tall fescue. Most sunny lawns are planted with tall fescue, as it tolerates drought and heat well. Fine fescue is happier in shadier areas. Many lawns are a mix of both, each growing where happiest.
You'll notice that many seed mixes have several species of grass, including tall fescue, fine fescue, and bluegrass. That's ok, since most lawns are not strictly full sun or shade at all times of the day.
We see a dead or brown area around the fine fescue. Fine fescue often 'melts' out during the heat and drought of summer, but the roots are still alive and come roaring back when conditions improve--such as now. Evenings are cooler, days are less severe, and we've had sufficient rainfall.
All the fescues are "cool season" grasses, and are happiest in spring and fall.
I have fine fescue in my rear yard, and it doesn't look anything like this (See first picture.). It does not grow in a radiating fashion like the pictures I sent. The other two photos are of the grass about which I wrote. It's brown now, whereas the fine fescue is still green. And it has an entirely different growth pattern, radiating from the center of the clump. Shall I send you a sample?
Sorry, but we do not accept plant samples and unfortunately the Master Gardener Plant Clinics are over for the season. In looking at your photos again it looks like you are dealing with 2 problematic weeds. The dead, tan, straw-like looking plant looks like nimblewill, http://extension.umd.edu/hgic/nimblewill
and the other looks like Roughstalk bluegrass,(the photo where the lawn meets the sidewalk), that would still be green and maybe even still growing now, http://extension.umd.edu/hgic/roughstalk-bluegrass
Both of these weeds are difficult to control.