Wet the underside of the foliage. Several applications at weekly intervals may be required. Resmethrin is effective and available as a spray or aerosol. Diseases Bacterial diseases Common hosts of bacterial diseases are diefenbachia, philodendron, English ivy, pilea, pellionia, aglaonema, dracaena, monstera, and pothos. These plants develop dark green, water-soaked spots that turn tan, dark brown, or black with a yellow border.
Spots can enlarge enough to cover an entire leaf.
Stems and petioles can also be infected. Nematodes are tiny roundworms that live in and feed on plant tissues, especially roots. Infected plants are often stunted, have leaves with brown lesions, and roots with nodules. Good sanitation including soil sterilizations helps to control nematodes. Stunting can also be seen.