I'm having trouble with my lawn. Over the past 3-4 years I have an increasingly large portion that turns light green in color from July-September. It's a beautiful dark green in Spring and also darkens back up in Fall as temperatures drop. It started a few years ago along the portion of my lawn that is above the downspout drain lines. The light green area has gotten larger each year since and now is a large portion of the yard. My lawn is bluegrass in the front and tall fescue in the back. It started in the back yard and is now also working it's way into the front. The soil is very sandy, never had it tested. I do run irrigation through the summer as the sandy soil dries very quickly as the summer heat arrives. I primarily use Ferilome Lawn Food plus Iron as my fertilizer. Not sure if any of that info helps, but I thought I'd throw it out there. The picture shows the area of light green grass that is most concentrated. I'm new to the forum so I'll try to figure out how to post a few more pictures in the replies. Thank you to anyone who has any suggestions as to of what this might be or what's causing it and how to fix it!