<p>The temperate genus <i>Porphyra sensu lato</i> has a long history of marine farming. Members of the genus are amongst the most common and economically valuable, commercially cultivated seaweeds on nets in the open sea. Species have a heteromorphic life cycle, alternating between a macroscopic blade and a microscopic, phase. The latter is an endolithic, shell-borne, filamentous thallus called the conchocelis which is cultivated separately within various bivalve shells in shallow ponds, on land. As a crop, its cultivation is accompanied by ever-increasing incidences of pests and diseases of both the blade and conchocelis phases. Serious damage is reported to be caused by the oomycete fungus <i>Pythium (Py.) porphyrae</i> and the chytrid <i>Olpidiopsis</i> spp., which have decreased the productivity of large-scale open sea farms especially in Korea and the northern coast of China. Interestingly, calcium propionate is effective combating oomycete infections. Early detection and development of resistant <i>Porphyra</i> strains, perhaps with some prophylactic, prebiotic treatments of low molecular weight oligoagars and selected probiotic, immune-stimulating bacteria might limit the damaging effects and economic consequences of this disease. In addition, cultivation nets are washed in acid to prevent carry over of disease-causing agents. As with any marine farming activity, epiphytes and grazers can also be issues faced by the farmers, but nothing as serious as the various rotting diseases. A summary of these studies is presented as a guide for rapid responses and applied management techniques for the amelioration of cultivation diseases, grazers, and harmful epiphytes affecting the two distinct phases of commercial <i>Porphyra</i> cultivation.</p>