Decline of Casuarina equisetifolia (ironwood) trees on Guam: Symptomatology and explanatory variables
R. L. SCHLUB (1), A. Moore (1), B. Marx (2), K. Schlub (2), L. Kennaway (3), M. Quintanilla (4), M. Putnam (5), Z. Mersha (6)
(1) University of Guam, Mangilao, Guam; (2) Louisiana State University, Baton Rouge, LA, U.S.A.; (3) USDA-APHIS-PPQ-CPHST, Fort Collins, CO, U.S.A.; (4) Northern Marianas College, Saipan; (5) Oregon State University, Corvallis, OR, U.S.A.; (6) University of Florida, Homestead, FL, U.S.A.
Phytopathology 101:S216

Guam’s Ironwood trees (Casuarina equisetifolia) are dying at rates that far exceed the norm for the region. The problem fits the classic definition of tree decline: symptoms are nonspecific such as the thinning of branches; tree health gradually deteriorates leading to tree death over a course of several years; and decline is attributed to a complex of infectious and non-infectious agents. However, Guam’s trees deviate from the classic model where mature trees are more prone to decline. Internal discoloration of the trunk and juncture of large branches was often traced to root and butt rot. By applying various modelling techniques to a set of 1427 individual trees, it was concluded that the presence of basidiocarps, termites, and improper tree care were significant explanatory variables for the decline. A data set created by GIS mapping was also evaluated; however, a reliable model has not yet immerged. At least 5 basidiocarp genera have been identified, of which Ganoderma and Phellinus are most likely contributing to the tree’s decline. Termites reported on Guam’s ironwood trees include species of Nasutitermes, Microtermes and Coptotermes. Other explanatory factors under study include typhoons Chata’an and Pongsona, a species of wasp belonging to the genus Selitrichodes, nematodes in the genera Helicotylenchus and Aphelenchoides, and the bacterium Ralstonia solanacearum.

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