The perennial geranium is generally pest free but can suffer from leaf spot, rust and occasionally mosaic virus. The major complaint I hear from gardeners is the foliage looks ratty in summer once the plant is finished blooming. Some species like the Big-root (Geranium macrorrhizum) and cultivars like Rozanne tend to have better looking foliage throughout the season. You can improve the looks of most perennial geraniums by cutting the discolored foliage back to the new growth that appears at the base of the plant. The young leaves will quickly expand providing fresh greenery for the remainder of the season. Viral diseases typically cause a unique pattern of discoloration in the leaves and eventually kill the plant. If your plant comes back healthy each spring you may want to consider moving it to a location with afternoon shade and remove old foliage when it starts looking bad. If you suspect a virus you should remove the plant and avoid planting another geranium or one of its relatives in this spot for several years.