To me it looks like chlorosis caused by a combination of overwatering and too high a pH.

Well that would be an easy fix! Our water is alkaline. Maybe I am watering too much now that it's cooled off some...

Should I rip all those leaves off now or clean them up after they fall?

rifis, can you post pics?

If it was me I would leave them, since aren’t they going to be getting their fall colors soon anyway?

In your zone I'd say just leave it alone. There are so few of them and the rest of the plant looks very healthy. It's just reacting to shorter daylight and getting ready for winter.

Actually, if your water is alkaline, it may not be an easy fix at all. Most of the northeast outside of major cities gets its water from wells. The pH of well water is determined by the pH of the soil the water is sitting in. So if your water is alkaline, there is a good chance your soil is also. Rugosas do not like that. They aren't as picky as multifloras, but definitely have a strong preference for acidic soil. It is something to keep in your head going forward. When we moved here from Philadelphia, learning a new zone was nothing compared to adjusting to a much higher pH.

Rifis, how much rain did you get in August? More or less than 10 inches?

Edited: watering a half gallon at a time falls in the category of 'sprinkling', and isn't a good idea. If you are going to water, let the ground dry out, then put down a good supply. That would be three to five gallons for a small rose.

Our water is not from a well... Hadn't thought that the soil might be alkaline because the rain up here is generally acidic and my Picea abies seem happy in the soil, but I will look into that. Thanks!

mad_gallica, we often get very heavy rainstorms that result in 3/4" to 1-1/2" or more. I thought that watering a little bit when it got dry out would tide them over. Is that wrong-headded?

Edit: I also figured that this would result in as little of the alkaline water as possible.

It's always better to water long and deep less often than a dribble every day. A half gallon of water won't even dampen the top inch of soil. When you water like that you force the plant to grow a lot of roots very shallow. You want to water deeply so the plant will send roots downward to where water reserves are. The deep roots will also anchor the plant in the ground better. A shallow rooted plant can heave out during high wind, flooding or freeze and thaw cycles.

To me they look OK for this time of year. I would leave them alone. I love rugosas. They were great in Alaska and they are great here.