In 1991, Phytophthora nicotianae was found on an onion sample submitted to the Agricultural Diagnostic Service Center at the University of Hawaii at Manoa. Although the initial sample originated from the island of Oahu, occurrence of this disease on other islands is very possible, since this pathogen has been found on all islands. In Hawaii, Phytophthora nicotianae causes leaf and stem infections on Chrysalidocarpus palm, Catharanthus , Dendrobium , poinsettia, impatiens, sage, spathiphyllum, and many other plants. This pathogen is especially serious because studies have shown it is not host specific. Disease on one plant can spread to adjacent plants of another species.
Free moisture is necessary for pathogen spread.
Sporangia need to be in water in order to germinate or release zoospores. Splashing water from raindrops or irrigation helps to move spores from infected plants to nearby healthy plants. The motile zoospores can swim in pools of standing water, drainage ditches or irrigation systems to infect plants far away from the original disease site. Non-Chemical Effective disease control begins with prevention and proper water management to minimize excess moisture on the plants. Avoid handling diseased and healthy plants at the same time since spores can be unknowingly transferred by workers during handling.