Last August, I had new sod laid down... pure Kentucky Bluegrass. It was completely awesome, company was great, etc. They told me to never fertilize myself, and instead have a trusted company do it, so I took their recommendation. This year, around April 17th, the company came and sprayed the first session with a hose (liquid based spray). The grass was still pretty dormant, I'm in SE MI and we had late snow and not a lot of rain. Since then, I watered the lawn one time around May 17th. We've gotten a lt of rain lately. About a week ago, so May 23rd-ish I noticed some brown / orange patterns appearing in the grass. It was odd because one was a crescent shape.

I sent pictures to the sod company and their first question was if I had fertilized it myself, said it looks like fertilizer burn.

So the fertilizer company came out and said there's no way it was their fertilizer and said that they think it was hydraulic fluid from my lawn care company. I told them that I cut my grass myself with a push mower. Then they said maybe another fertilizer ocmpany did our lawn by mistake. Thing is, I have security cameras and after reviewing the past 6 weeks, the only thing to have walked on the grass, except for me cutting, was the fertilizer guy, some squirrels, and a couple of rabbits.

Thoughts on what this could be? I mean, is it possible that this is a fertilizer issue? I know it's not bugs or grubs - I dug up a sample and saw nothing.