Many palm fronds turn yellow and die, from the bottom up. On coconut palm, all the nuts usually drop. The nuts are black where they were attached to the flower stalk. New flower stalks are blackened and do not set any fruit. After several monhs, all the fronds and the bud have been killed. Shortly thereafter the entire palm top falls off, leaving only the bare trunk. No insects are visible.
Planthoppers are difficult to detect and control. Lethal yellowing cannot be cured. Avoid planting susceptible palms. Remove infected palms to avoid spreading the disease.