That does look like powdery mildew on a plantain leaf (Plantago sp).

I wouldn't worry about it, if it's in your lawn. If these plants are growing in your flower beds, you might want to pull them or remove the leaves and put them in the city compost pickup. Powdery mildew is not contagious. It is a fungus spread by wind or water (splashing rain). However, it is generally host specific. That means that the powdery mildew on your plantain will not jump to another plant in a different plant family.

Powdery mildew outbreaks are often weather dependent. This year, weather has been particularly conducive to powdery mildew. I think that you will find it is gone in the spring and, if we have a dry year, it might not come back.

Here is a good article from the University of Missouri that explains it in more detail.