Not sure what has been affecting this. It started about one month ago. At that time I cut out an affected area about two feet by two feet. Did okay until a few days ago. In fact new growth appeared where old was cut out. Now it's spread to about a 4 foot by two foot area. It's watered every five days or so, gets partial sun this time of year. Always stays moist. Been hot and... yes muggy at night.
No dog. Just a local dog every few days, but he likes containers to pee on. Besides he couldn't get to that spot this time of the year. Too much to navigate over and through. I've come to live with it. Would have been nice if the area remained full all year. Growing back already.
There don't seem to be many problems associated with lysimachia nummularia. Best guess I see is an overwatering issue, which can lead to secondary problems. Have you had cool summer? I would check the soil moisture level before you water the next few times and removed all dead and possibly diseased plants & roots to prevent it from spreading.
Check out this link, scroll all the way to the bottom and read the parts on drowning.
Reason for watering is lack of rain. Only four inches since May 26. It drains quite well and the area stays moist this time of year with increased shade. That has led me to cut back and eliminate watering the last three weeks. I don't think it's over watering as it's now showing it's ugly head in a large container that gets watered once per week. Cool? Hot by comparison. But I have very poor airflow in the area as it's surrounded by large hills. Kind of like a mini valley amongst woods. That could be a cause as well. Thanks for the suggestions.
I'll say there's been a lack of rain and I have a similar problem with creeping jenny. Actually I also have blue star creeper in the same area showing similar bare spots. In addition there is some ajuga, some of which I've lost due to crown rot fungus which I first noticed last year. As a result of the fungus I did not water the area much until recently and at this point I'm thinking I should water more. I am looking to see if the laurentia will spread back into the bare areas with watering. Well, the creeping jenny too. I finally got a sprinkle on the garden tonight but the moisture situation is getting desprate around here as it must be in Ellijay, which is not too far away.
I'd agree with Back40. I have the same problem as KD with my 'Aurea" Creeping Jenny in Oregon. It's gorgeous in the rainy springtime, but once the dry season starts, I get big brown patches, and by winter, the whole area is brown, in spite of light watering 3x/week.
It's unlikely to be overwatering. Jenny is often recommended as a pondside plant, and I found this on Plant Guide on line:
" This cultivar can withstand damper soils than many other types of ground covers and can tolerate limited foot traffic. Grow in a moist, but well-drained soil, rich in organic matter. Soil should not dry out in summer. Full sun or partial shade, but color is best in full sun."