Lethal Yellowing is a deadly disease which affects palms. It has been seen in dozens of species of palms, but it is most common in Coconut and Christmas palms. Lethal Yellowing is a phytoplasma which is thought to behave like a primitive virus and is transmitted by the leafhopper bug Myndus Crudus. The leafhopper feeds on an infected palm and ingests the phytoplasm. Once it has fed on an infected palm, the leafhopper can infect other palms that it feeds on.
Lethal Yellowing can only be spread by the insect whos body metabolizes the organism and makes it transferable. Scientists have taken active lethal yellowing phytoplasm and injected it into healthy palms and the disease never appeared.
Growers have tried cross breeding different coconut palms to try to come up with a species that does not get the lethal yellowing disease but no palms have offered any reliable resistance to the disease. You can identify Lethal Yellowing by visible symptoms on the palms. The earliest symptom is a browning, then later a blackening in the inflorescence. The inflorescence is the name for the cluster of flowers that eventually grow into coconuts. Once the inflorescence starts discoloring, the palm is almost surely affected with lethal yellowing.