I planted a small container of rock cress, arabis caucasica 'variegata' in full sun next to a piece of shale, and after a couple of weeks most of the plant withered up. It looks like a fungus problem. I have not seen any comments to this effect from anyone. Can anyone give me some insight on this. I had gathered the plants were extremely hardy and I did not think I would have to worry about something like this.
Is the arabis still in a container? What kind of soil is it growing in (e.g. clay, sand, peatmoss, gravel)? How often have you been watering it? Does it have good drainage or could the roots be waterlogged? Did it flower spectacularly before withering?
Arabis does well here in my climate... lots of rain and cool summers. I wonder if it is suffering from the heat of your summer. I would trim it back and move it away from the heat of the sun for awhile. Maybe arabis dies back in areas where there are hot summers. Many spring bloomers do. It is an evergreen plant here in my mild zone 3.