Phytophthora is a water mold (Class Oomycetes, formerly a fungus-like protist) that is found throughout the world. Under favorable conditions (high moisture and temperature) it produces large numbers of motile zoospores that can swim in water for short distances. These zoospores are the infective agents that may be transported in rain or irrigation to the roots. When zoospores contact roots they encyst, germinate and enter the root tip resulting in rot of the entire rootlet.
Foot rot or gummosis occur when zoospores splash onto a wound or bark crack around the base of the trunk. Additionally, there is an association of Phytophthora root rot when roots are damaged by citrus root weevils, particularly Diaprepes abbreviatus. Root stock susceptibility depends on which Phytophthora species are present and the presence of favorable soil, water and environmental conditions.
Other Common Names
Phytophthora foot rot, root rot, brown rot, gummosis, and Phytophthera-Diaprepes (PD) complex
Serrano, D., Serrano, E., Dewdney, M., and Southwick, C. (2010). Citrus Diseases. USDA/APHIS/PPQ Center for Plant Health Science and Technology. [09-14]