Citrus phytophthora diseases: Management challenges and successes

Abstract

Phytophthora spp. are present in nearly all citrus groves in Florida and Brazil and phytophthora-induced diseases, especially foot and root rot, have the potential to cause economically important crop losses. Disease-related losses due to root rot are difficult to estimate because fibrous root damage and yield loss are not always directly proportional. Challenges from phytophthora diseases have been addressed in both countries by enacting phytosanitary requirements for production of pathogen-free nursery trees in enclosed structures, propagated from indexed and certified pathogen-free sources, in conjunction with several other cultural management practices. In Florida groves, a statewide soil sampling program provides growers with soil propagule counts to estimate the damage that Phytophthora spp. are causing to fibrous roots. The results can be used along with rootstock tolerance, soils, topography, irrigation, and drainage to make a decision for the need to treat with fungicides in addition to modification of cultural managements. Huanglongbing (HLB), caused by the psyllidtransmitted bacterium Candidatus Liberibacter asiaticus (Las), was detected in Brazil and Florida in the mid-2000s. Given the increasing incidence of HLB and deterioration of root density due to Las damage, research experiences and current phytophthora data trends suggest the need for more comprehensive management of root health by reducing the impact of abiotic and biotic stresses, including the interaction with Phytophthora spp.