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Disease Management

To discourage the spread of lethal yellowing in the tropics, commercial movement of living palms from locations affected by lethal yellowing to disease-free areas is generally not permitted. However, quarantine requirements vary according to the specific geographical areas involved. Technical guidelines for the safe movement of coconut germplasm have been developed under the auspices of the FAO International Board for Plant Genetic Resources.

Chemical control of lethal yellowing is accomplished with the antibiotic oxytetracycline HCl (Terramycin), which is administered to palms as a liquid injection into the trunk. As a therapeutic measure, systemic treatment on a 4-month treatment schedule should begin as early as possible after the onset of symptoms. Palms with >25% discolored leaves should be removed, since they are unlikely to respond to Terramycin treatment. The antibiotic can also be used preventively to protect palms when lethal yellowing is known to occur in the area. The dosage recommended depends on the size of the treated palm. The approximate cost of Terramycin ranges from $1.50 to $4.00 per palm per treatment, depending on the number of palms treated. Control of planthopper populations with insecticides is currently insufficient to justify repeated applications in landscapes or palm plantations.

Use of host resistance represents the most practical long-term tool for managing lethal yellowing. Many palm species are not susceptible to lethal yellowing and provide important alternative choices for ornamental landscape plantings. To date, lethal yellowing has not been reported on most palm species native to Florida and the Caribbean Basin. These include Sabal palmetto (cabbage palm), Roystonea regia (royal palm), Acoelorrhaphe wrightii (Paurotis or Everglades palm), and Thrinax species (thatch palms). On the other hand, Cocos nucifera (coconut), Pritchardia spp., Adonidia merrillii (Christmas palm), and Phoenix dactylifera (date palm) have sustained consistent losses and are not recommended for widespread landscape use in areas where lethal yellowing occurs.

Coconut cultivars, such as the ‘Malayan Dwarf’ or hybrid ‘MayPan’ (‘Malayan Dwarf’ x ‘Panama Tall’), have exhibited acceptable levels of resistance in most areas. However, recent reports of lethal yellowing losses in ‘Malayan Dwarf’ and ‘MayPan’ of 70% and 83%, respectively, at localized sites in southeastern Florida and 95 to 99% in Jamaica cast doubt on the long-term resistance of these cultivars.

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