DISTRIBUTION: Florida, Mexico, many Caribbean countries, West Africa ( Togo, Nigeria, Ghana), East Africa ( Tanzania, Kenya), Belize, Honduras. LY has been known in Texas.
DESCRIPTION: The causative agent of LY is a phytoplamsa (Fig 1 – stained soybean phloem cells with phytoplasma particles). Phytoplasmas are microscopic single celled organisms lacking a nucleus or membrane bound organelles. They do not have a cell wall but are bound by a plasma membrane. They are found in the phloem (food-conducting tissue) of their plant hosts and in the gut of certain insects.
HOSTS: LY affects 34 species of palm trees including coconut and date palms.
DAMAGE: The first symptom (Fig 2) is a browning then later a blackening in the inflorescence (cluster of flowers that become fruit). After this comes heavy fruit drop (Fig 3a) and a premature browning or yellowing of the fronds (Fig 3b). The fruit may appear water soaked. The fronds will turn brown or yellow from the oldest growth first and then eventually the newest fronds in the center will turn brown. The spear leaf collapses and the entire crown falls from the tree leaving a ‘telephone pole’ stalk (Fig 4).
INSPECTION TIPS: To the untrained eye, LY may be confused with such diseases as fungal bud rot, nutrient deficiencies, insects, nematode and lighting damage.
The definitive stage for LY is the blackened inflorescences on palm trees. The inflorescences of healthy trees are a golden yellow. Most of the fallen fruits will have a black area immediately under the calyx (group of leaf-like structures that once enclosed the flower found on the stem end of the fruit).
LIFE CYCLE: The incubation period of LY is six months to two years although it only takes 3-6 months after symptoms appear for a tree to die. LY reproduces in the phloem tissue of palms. The tissue becomes packed with phytoplasma causing a physical obstruction to the flow of nutrients that eventually kills the tree. LY also spends time in the gut of an insect vector. The only established vector for spread of LY in FL is a leafhopper, Myndus crudus (Fig 5). Adult Myndus crudus feed on palms, exchanging fluids in the process, and thus spread the disease from palm to palm
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