Question
Our new lawn is about two months old.  This is a sod lawn.  I have been watering it every two to three days for about 30 minutes to 45 minutes each time.  I am noticing that mushrooms are appearing and some patches of yellowing.  Is this caused by too much watering?

Answer
It very well could be.  Mushrooms appear when there is plenty of organic matter, AND plenty of moisture.  The yellowing could be a disease caused by too much water.  Give the sod a few light tugs to see if it's fully knitted to the soil.  If so, back off on the watering to about 2X per week.  This could take a little playing around to figure it out, but it sounds like you've got the right idea and you seem to understand the issues.

Don't worry about the mushrooms though, they'll go away on their own when they dry out.

-C.J. Brown
www.TheLawnCoach.com