Controlling

Information Provided by: COLLEGE OF TROPICAL AGRICULTURE AND HUMAN RESOURCE

University of Hawaii

Once trees are infected, death from the disease appears to be inevitable, and several hundred trees have been lost throughout the state since 1970. Because the host range of this Phytophthora appears to be confined to coconut, eradication and exclusion are feasible control options.

All infected trees and nuts should be de­stroyed by incineration or deep burial. Prompt removal of diseased trees will reduce the probability of soil contamination with the path­ogen. Oospores of most Phytophthora species are able to survive in soil without the host plant. Removal of diseased material will also prevent spread of the fungus to healthy trees.

Many diseased trees have been observed in wet windward areas of Kauai, Hawaii, and Oahu. Growers should avoid collecting coconut plant­ing material from these areas. Since mature trees may be infected yet remain symptomless for many months, careful selection of clean nuts and healthy seedlings and trees is necessary. Stock plants or young seedlings should be grown in relatively dry areas to minimize establish­ment of the pathogen on new plants.

Because the epidemiology of this disease in Hawaii is not known, the means by which it spreads is not specifically known. Based on studies of other Phytophthora diseases, wind-driven rain, insects, or other small animals are probably important factors in the spread of the disease. Moisture strongly favors the growth, spore production, and spread of Phytophthora and disease development by this fungus. Oospores of the fungus occur in very large num­bers within diseased husks and trunks. These thick-walled resistant structures allow the fungus to survive for long periods in a dormant state. The fungus is probably seed-borne as oospores in the husk.

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