Good afternoon Bruce and thank you for reaching out to ask2.extension.

I believe what you have is rust.  It is something that happens with new grass when it’s dry and watered artificially.

I am attaching an article for you to read on rust.  Go to extension.umn.edu and search what’s wrong with my plant-turf-discolored turf blades.  It will tell you about it and how to fix it.  It really isn’t something to worry about too much.

I hope this helps.

It could be Bruce and that you’ve caught it early. that makes sense if it’s not coming off on your shoes, etc. and since you are watering new grass next to it.  Here are some tips  for dealing with brown spot.

There are a variety of reasons your lawn may develop Brown patch, including high heat and humidity, excessive nitrogen, moisture, poor soil damage, too much thatch, and compacted soil. In some cases, you can’t prevent your lawn from developing Brown thatch—after all, you can’t control the weather.

While most lawns recover without chemical intervention, in some cases you may need to combat Brown patch with chemicals. This is best left to professionals. Different fungicides will start showing results at different times. For some, you may see improvement in as little as 24 hours.

Excessive moisture can lead to Brown patch, so be sure to water your lawn either early in the morning before 10 a.m., or between 4 p.m. and 6 p.m. to ensure that the grass dries out fully before nightfall. If you allow your grass to remain wet all night, it will become more susceptible to disease and pests.

Fertilize carefully: Too much nitrogen can lead to Brown patch. Try to avoid fertilizing your lawn when it’s hot and humid out, and select a fertilizer with a suitable NPK value. NPK refers to the proportions of nitrogen, phosphorus, and potassium in the fertilizer. You can ask your local gardening store about which fertilizer may be best for your lawn.

Improve air circulation in your soil: Aerating and dethatching will reduce humidity, making it less likely that Brown patch will develop. Aerating is done using a core aerator or spike aerator, either pulling many little plugs or “cores” of soil out of the ground, or perforating it with many small holes. Dethatching, done with a dethatching rake, removes a layer of organic material that can smother grass. When you aerate and dethatch, you allow the grassroots to access the water, air, and nutrients they need more easily.

I’m wondering if you try to water only the new grass for some time and see if it clears up on its own.  If not you may have to talk to a lawn company.