"Now, the affected area does coincide with the area where I left a couple of plastic tarps for a few hours to dry out -- they had been used to suppress weeds in the garden -- but they were just there for a few hours so I don't think that's the problem."

The tarps block air flow and trap moisture making them the perfect breeding ground for disease. That could be one possibility.

Tarps also block light which can make grass lose it's color.

It doesn't take long, a few hours is enough. I've noticed this happen if I forget something on the lawn. A bucket, shrub trimmings, a hose, etc. Not sure what it was but for me it went away after a few days without doing anything.

It doesn't take long for plastic to damage a lawn on a sunny day. If those spots correspond to where you had the plastic drying, I'd suspect the plastic. If the grass died and it's fescue, you'll probably need to overseed those areas, but if it's just yellow, it may well bounce back.

Thanks very very much guys. Yes, I suspect you are right. It is just too much of a coincidence. One detail I omitted: The grass turned yellow several days after I left the tarps there, but I guess maybe it took a few days for the effects to show.

Well, I will be back at the house on Sunday and I'll see then what the situation is. (Now I have to look up what "overseed" means....)

I once found a perfect circle of yellowing grass on my lawn. It was really puzzling to me until I finally realized that I had put the lid of the grill on that exact spot a few days earlier while I was lighting the grill.

Overseeding is seeding an existing lawn. Some grasses (most fescues, for example) don't spread and develop bare spots over time. When that happens, they need to be overeeded for the bare spots to fill in.

If the tarps were only there for a few hours, then I don't think it was lack of light or moisture, but the heat: the grass underneath the plastic tarps may have been cooked if it was a hot day.

Yes, it might have been that as it was a warm day. Not hot, only about 70, but warm by Catskills standards.

I have a question about overseeding, in case that is necessary (I will find out when I get to the house over the weekend):

I see from articles on overseeding that one has to water the overseeded area for two weeks after seeding. Unfortunately we are not going to be there that long, as this is a summer/weekend house, and it does not rain every day.

I saw that there is a product called GrassFast that keeps the water on the seeded area, but it seems to have limited availability and I was wondering if there are substitutes.

I am glad to learn about overseeding, as I had not heard of it and there are areas of my property that need it other than this one!

Thanks again.

From the sounds of things, you might lose some of the grass in those spots, but not all of it. And the surrounding grass may fill in (depending on the kind of grass).

If I were you, I'd wait until this fall to see how bad it is.

One thing you can do is wait until it is too cool for the grass to germinate and put the seed down then. It will sit there over the winter and work into the soil with freeze/thaw cycles and with the snow melt. When it warms up enough, it will germinate with the natural spring moisture. That's probably the best way to get grass to grow from seed when you can't be there to water it.

Check the weather for the next week. A lot of the area is going to have another week of rain that might help.

A simple hose end timer and sprinkler setup is pretty cheap and will water the seed for you. Do a search for sprinklers for small lawns and you can find some examples of what I'm talking about.

GrassFast and products like that which are sheets are expensive and really meant for for slopes where you don't want the seed to run off with the rain or irrigation. There are other products like paper mulches you can buy for much less. There are also specially coated seeds like Scotts new water saver stuff but none of those items will let you go a week without watering.

I never heard of grass fast but I've seen pennington seed mats at home depot.

As everyone else has said, fall is the best time to seed in this region but if you don't mind spending some money on seed and a sprinkler you'll need anyway you might get it to fill in a little bit but you'll probably need to do it again in the fall.

It's not like we're talking about the whole lawn and hundreds of dollars worth of seed here. I'd throw some down and see what happens.

I'm going to be at the house on Sunday. We're staying through Saturday, and then we'll be back on Wednesday before the July 4 holiday, and then staying through Tuesday. So actually we'll only be away for a few days over a two-week period.

Since this is indeed not a large segment of the lawn--we're only talking about maybe $10-20 in seeds I would imagine--perhaps I can give a bit of overseeding a try? Assuming its needed, of course.

yep, as several people suggested, the yellowed area has gradually come to life. Thanks much for all the help. I have another issue I'd like to deal with, but I'll start a new topic for that

Hi, Thank goodness I found this website. I have just about the same problem. Just a few months ago I set sod for the first time in my life by myself just below the 400 sq footage and it turned out great. I did alot of procrastination within that time in getting a lawn mower. So months past and my grass got so long it did not stand straight anymore and also noticed some thinning. Just a couple days ago I finally decided to mow it and noticed it was very yellow/dying grass underneath it all. There is still pretty good amounts of green in it, but my question is it too late to fight off the disease and thatch it has developed if disease is what it is?
THANK YOU

Acme--You probably should have started a new thread for this since it's a different question, but I'll try to answer anyway.

It would help if you'd tell us where you live. You don't have to be too specific if you're concerned with privacy, but your profile only shows United States and it's a large country with lots of different climate conditions and grasses.

If you let it get really long before mowing, you probably took too much off with the first mowing. That would stress the grass, but the grass should recover. At least that's the case if you do it once. If you do that every time, it's a different story. The general rule of thumb is that you don't want to remove more than 1/3 of the blade when you mow. So if you're mowing to 3 inches, try not to let the grass grow more than 4.5 inches tall.

At this point, you probably don't need to do anything except let it recover.