Leaves Turn Pale, Brown because of Too Much Sun
Although spotted deadnettle can handle some sun if it has to, it is most comfortable in the shade, especially during the afternoon heat of summer days. Full sun at that time may scorch leaves, injuring them and reducing plant vigor. It may be necessary to move the plants to a more shaded spot. This may also happen in the winter when the shade trees lose their leaves and bright winter sun glares on deadnettle foliage. A light covering of evergreen boughs will protect plants from winter sun.
Spotted deadnettle is remarkably free of pest and disease problems.
Ragged Holes in Leaves caused by Slugs
Slugs are essentially snails without shells. They are commonly 1 to 2 inches long--although some species grow up to 8 inches and may be white, gray, yellow, and brown-black. Slugs are attracted to moist, well-mulched gardens and acidic soil, especially shade gardens, where they feed at night on a variety of plants. Slugs rasp large ragged holes in leaves and stems with their file-like tongues, and then they hide under boards or leaf litter during the day.
The best way to control slugs is to trap them early in the season before they get out of hand. Use commercial or homemade traps baited with beer. A pie plate or other shallow container works well. Slugs, attracted to the yeast in the beer, climb in and drown. As soon as slugs appear in the trap, increase the number of traps to catch the whole first generation before they can lay eggs and multiply beyond control. If slugs persist, spread aluminum sulfate on the soil around the patches of spotted deadnettle. For more information see the file on Controlling Slugs
Spotted deadnettle does not commonly suffer from any diseases.