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Excerpts from Jim Conrad's
Naturalist Newsletter
from the May 1, 2011 Newsletter issued from Mayan Beach Garden Inn 20 kms north of Mahahual; Caribbean coastal beach and mangroves, ~N18.89°, ~W87.64°, Quintana Roo state, MÉXICO
LETHAL YELLOWING DISEASE IN SIAN KA'AN
On the Web an author with the United Nations Environment Program writes that during the ten years between 1998 and 2008, 95% of Sian Ka'an's Coconut Palms were destroyed by Lethal Yellowing Disease, often known as LYD. The main reason for such a disastrous decline is that over the years people had replaced native ecotypes of relatively slow-growing Coconut Palms producing odd-shaped and often smaller coconuts, with a fast-growing kind producing very large, spherical coconuts. So, at the root of the problem is displacement of diverse, native Coconut ecotypes with a monoculture.
You can see a typical Coconut Palm dying of Lethal Yellowing Disease in Sian Ka'an below:
A close-up of a typical infected frond is shown below:
LYD is caused by a special kind of bacteria known as a phytoplasma. Phytoplasmas were unknown to science before 1976. They live only in plant phloem -- phloem being the part of a plant's vascular system transporting photosynthesized glucose and other organic nutrients to all parts of the plant. The phytoplasma disease organism is transported from plant to plant by common, piercing-and-sucking insects known as planthoppers.
In Sian Ka'an it's often the case that palms weakened by LYD are attacked by a large beetle, the Palmetto Weevil, Rhynchophorus cruentatus, whose grubs tunnel through palm-trunk centers, killing the palms faster than if only the disease were involved. As we drove around, Marcia showed me how to distinguish between palms dead and dying from LYD, and those killed by weevils attacking trees weakened by LYD. Those dying strictly from LYD first lose their lower fronds. Palms killed by weevil grubs die from the inside-out, all fronds collapsing together, as pathetically shown below:
At least 36 palm species have been documented suffering from LYD, and the Chit Palm, the other abundant palm, a fan palm, so characteristic of this area, is one of those vulnerable to the disease. However it seems to be more resistant than Coconut Palms.
Needless to say, anyone planting Coconut Palms should avoid using the fast-growing variety producing large, round coconuts. Instead, native ecotypes that may be slower growing and producing small, irregular-shaped coconuts should be chosen.