Question
My lawn is now 7 years old---I put it in myself. The first few years I had a lawn to die for. The past couple of years I've experienced a number of patches (4"-18" diameter) which have died out over the winter (this year was worse than previous years). I scratched these up this spring and many are coming back--some are not. Then, too, over the winter I had voles do a number on several areas. Again I scratched the areas up this spring and some--not all--are coming back. Should I wait longer? My lawn is irrigated, I have a soil sample done every 4-5 years. The lawn is fertilized spring and fall (with a mix I get from the local co-op which is formulated based on my soil sample). Don't know what else to try. Any suggestions? I'm located in NW Wisconsin.  

Answer
Your fertilizer and soil sampling is right on target.

The winter kill could be due to a number of reasons. Sometimes a mature lawn gets "invaded" by weedy grasses which start to grow in the existing lawn and crowds out the regular grass. these spots will then die back in winter if the weedy grass is not winter hardy to your zone. There is not much you can do except to scracth it out, and resow.

Another option could be snow mold caused by fungus. typically this is related to fertilizing too late, or a heavy snow cover which interfer with air exchange.

Before the first winter snow blankets the lawn, apply a fungus control product (make sure it does not have fertilizer mixed in with it as some do). Also, fertilize in early fall rather than late fall. Also cut the lawn a bit lower going into winter. I normally recommend late fall fertilization, but if you have snow mold, it is worth to cut back to see if it improves.

Other steps to avoid snow mold includes avoiding excessive traffic on the lawn when wet in winter, and improving drainage (if possible).

You may want to take a look at these two article, too:

http://www.spring-green.com/snowmold.htm

http://www.uwex.edu/news/story.cfm?id=326&style=print_story