Growth and Refoliation of Koa Trees Infested by the Koa Moth, Scotorythra paludicola (Lepidoptera: Geometridae)

Abstract

Since the early 1900s, four major infestations of the koa moth, Scotorythra paludicola (Butler), have defoliated koa (Acacia koa Gray) stands on the island ofMaui. After trees on 7564 ha of the Makawao Forest Reserve were damaged in 1977, a study was begun to determine growth and refoliation response of completely defoliated tree s in a stand previously subjected to three different silvicultural treatments. Relative growth rates before defoliation ranged from 5.7 percent to 14.2 percent per year. Trees on thinned-and-fertilized plots showed significantly greater relative growth rates than control trees. The relative growth rates of trees on plots that were thinned only or fertilized only were not significantly different from those of the control trees . After defoliation, relative growth rates ranged from l.l percent to 4.3 percent with differences between treatments not significant. The 71 percent reduction in growth after defoliation was statistically significant. About one-third of the sample trees died within 20 months of defoliation.