Plants that are treated with silicon (Si) show enhanced host resistance, perhaps because the accumulation of silica in host cell walls deters the pathogen from penetrating host tissues. In this study, oil palm seedlings were treated with five Si sources (silicon oxide, potassium silicate, calcium silicate, sodium silicate, and sodium meta-silicate) at four concentrations (0, 800, 1200, and 2000 mg L1) to evaluate the effects of Si treatment on the growth and resistance to G. boninense of oil palm.