Oh, those hollyhocks! They are known for developing diseases that end up giving them 'ugly legs'. Keep the dead leaves picked off and throw them in the garbage. Next year, plant them in a spot with full sun and good air circulation. There isn't much you can do, other than to plant other things at the base of the plants to cover them up. I always plant them behind shorter annuals or perennials, because more years than not, they drop their lower leaves.