Red Ring
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Figure 1. Cocos nucifera with premature death of older leaves. Photo by M. L. Elliott.
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Figure 2. Cross-section through Cocos nucifera trunk exhibiting typical ring discoloration pattern near the outside edge of the trunk. Photo by R. M. Giblin-Davis, University of Florida.
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Scientific name of pathogen
Bursaphelenchus cocophilus: Kingdom Animalia, Phylum Nematoda
Hosts
Palm hosts (natural and successfully inoculated) for the nematode that causes red ring: Acrocomia aculeata, Acrocomia intumescens, Astrocaryum standleyanum, Attalea cohune, Bactris gasipaes, Bactris gasipaes, Cocos nucifera, Elaeis guineensis, Euterpe pacifica, Jessenia polycarpa, Mauritia caribea, Mauritia flexuosa, Mauritia mexicana, Maximiliana maripa, Oenocarpus distichus, Phoenix canariensis, Phoenix dactylifera, Roystonea oleracea, Roystonea regia, Sabal palmetto.
Distribution
The disease does not occur in the continental U.S., but does occur from Mexico southward into the northern countries of South America and in the Lesser Antilles.
Symptoms/signs
For Cocos nucifera, early symptoms include premature nut fall, death of the inflorescences and premature discoloration and death of older leaves. Leaf yellowing begins at the leafletleaflet:
divisions of pinnate leaves
tips, progressing towards the rachisrachis:
the axis of a leaf beyond the petiole or an extension of the petiole into the leaf blade
. Eventually, the leaf becomes necroticnecrotic:
see necrosis
, and it may break at the leaf baseleaf base:
the basal portion of a leaf petiole that is attached to the stem
to hang around the trunk (Fig. 1). The leaf symptoms progress upwards through the canopycanopy:
the cluster of leaves borne at the tip of the stem
to younger leaves. A cross-section through the trunk reveals a distinct brick-red to brownish-red ring that is 1 to 2 inches wide and is located 1 to 2 inches from the edge of the trunk (Fig. 2). The disease is normally observed in palms that are at least 2 to 3 years old.
Similar leaf symptoms are observed in Elaeis guineensis, but the ring is either a brown, cream or rose color.
In older palms (20 years or more), a little leaf symptom is observed. The palms begin producing very short leaves, and leaf size continues to decrease until only a leafless rachisrachis:
the axis of a leaf beyond the petiole or an extension of the petiole into the leaf blade
is produced. No "ring" symptom is observed in trunk cross-sections of such palms.
May be confused with
If the palm is a Cocos nucifera and less than 20 years old, canopycanopy:
the cluster of leaves borne at the tip of the stem
symptoms of red ring could be confused with lethal yellowing.
Additional comments
The nematode is vectored by palm weevils (Rhynchophorus palmarum, Dynamis borassi and Metamasius hemipterus).
