Looks like fungus unless someone is sprinkling some type of toxic chemical around. Is it just that one area and spreading outward? Looks like bentgrass from the picture.... Not the best identifier though. So much looks so similar.
That, in my opinion is not grub’s causing the problem. Just looking at the pattern leads me to say that. Possible red thread, which can be active year round in some areas. It looks to have a slight pinkish/salmon color, but I don’t see the reddish mycelium because I can’t enlarge the pic enough without it getting fuzzy, so tough to tell.
What have your growing conditions been like? Humid and upper 60’s overnight for a period of time? Fungus likes this. Can you take a sample and have it analyzed? Try taking a real close up pic and posting again. Something might be visible that we can’t see in this one.
red thread / pink patch has my vote. Generally it’s from constant wet conditions, your slow release fert is gone from rain/ overwatering and it’s starving. What are your temperatures, recently very wet? What’s your watering schedule? I like liquid fungicides for diseases that attack plants from the top down. You’ll need a different A.I. from Scott’s disease x.
Walkonwater makes a good point. I wanted to use the Scotts Disease-X for my dollar spot--but it does not list dollarspot as controlled on the label.
Above makes a good point--red thread is a possibility. Common on perennial rye grass. Worse, if it is an old-fashioned cheap perennial rye. Worse if the fertility is low.
Thanks for the replies. Yes, it's always wet here except the summer. Temps have been low 50s during the day low 40s at night. It did start showing up at the end of the summer though. It was being watered 15 minutes per day using the cheap "misting" type rain bird heads.
The entire lawn is about 2000 sq ft, and these spots are all over it. I work for a school district and maintain quite a few yards and sports fields and this is the first time I've seen this. I'll try and get some better close up pics.
Fusarium patch, which I think is now called summer patch has a frog eye pattern. Don’t see that in those pics. Also, there are liquid systemic fungicides available. Once you have a positive ID, then you will now what fungicide to use.
Both dollar spot and red thread usually show up on low fertility lawns. Red thread is more of a cosmetic blemish while dollar spot has the potential to be more destructive
You can cure, or at least minimize, most of those unsightly problems using cultural habits.
Do not mow when you see the mycelium present on the blades, usually early morning until it burns off.
Watch weather for precipitation totals. Do not water if lawn is getting enough rain.
Water deep and infrequently as necessary.
Don’t let the lawn starve for nitrogen.
If you desire to (attempt) to minimize or control the disease, the use of fungicides can be expensive and if you are not watchful you may use the incorrect control agent for your disease.
If that disease is red thread, and whoever said get it tested is correct; the Scott’s Disease-X (active ingredient Azoxystrobin) you used has a high efficacy rating to cure/control red thread. As does:
chlorothalonil, iprodione, propiconazole. I do not know what the Brand Names of those products are sorry. And the good thing is they are all classified with different FRAC codes. That essentially means they attack the pathogen using different modes of action. Which is good as long as they are all effective against that specific disease.