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Red Ring Nematode
Synonym: Rhadinaphelenchus cocophilus
Rhadinaphelenchus was designated a junior synonym of Bursaphelenchus by Baujard (Revue Nematol 12:323-324, 1989) as it has all the same characters including a subterminal bursa; but differs only in having a greater length to width ratio ('a' ratio), being very long and slender.
|Male: Paired spicules
with prominent disc expansions at distal end.
Caudal papillae occur throughout the Aphelenchina.
|Similar to Aphelenchoides,
but very slender and has sclerotized lip region.
Drawing from Cobb and Maggenti
Nematode is 1.0-1.2mm long.
Female: Genus is characterized by vulval flap.
West Indies, South and Central America.
No California pest rating.
Naturally infects coconut and oil palms, can be artificially inoculated into cabbage palm and a few others.
For an extensive list of host plant species and their susceptibility, copy the name
select Nemabase and paste the name in the Genus and species box
Nematode has a 10 day life cycle, and can migrate and survive in soil, especially moist areas, but tree to tree spread seems minimal.
Nematodes can be transmitted by putting infected tissue in soil near healthy trees, but nematode survives free in soil only 3-4 days.
Insect vector is Palm (Coconut) Weevil, Rhynchophorus palmarum.
Nematodes are carried on body surface and also enter body through spiracles and mouth.
Transmission to leaf axils occurs as beetle feeds.
|Nematodes also aggregate around ovipositor and are injected into soft tissue as beetle deposits eggs. Beetle larvae hatch and tunnel into tissues, pupate, emerge, become infected and spread nematodes. There is some evidence to suggest that nematodes may persist in beetle larvae through molts, but this is unclear.|
|Coconuts are especially susceptible for 2 years before and after start of fruit bearing. Older and younger trees are more resistant.|
|Older leaves become chlorotic and die; younger leaves turn
yellow; green nuts and unopen flowers are shed. Tree may show
"little-leaf" symptoms (see Fig.).
Trees may die 4 months after first symptoms appear.
Symptoms include band of discolored, reddish-brown tissue about 5 cm from edge of leaf stems; discoloration extends into leaf petioles. Red ring (3-4 cm wide) may appear up to 8'(2.4 m) above soil line. Nematodes are numerous in and around the discolored tissues; adults are usually located at inner edge of red ring.
Up to 5000 nematodes can be found per gram of tissue; greatest numbers occur 6-12" (15-30 cm) below upper limit of ring.
Roots are similarly discolored, with soft, spongy cortex.
There is apparently a phytotoxin in the red ring. Damage causes reduction in water uptake by tree.
Discoloration occurs before appearance of leaf symptoms (and can be detected by stem borings); allows roguing to prevent spread.
|Roguing of diseased palms: stem boring to determine presence
of red ring followed by cutting and burning infested tissues removes sources of
Bait traps for vector control: ground coconut shells and Sevin (Cocosev) in Trinidad or use of Lannate bait traps.
In Mexico, Palm Weevil control has reduced incidence of nematode infestation from 10% to 1%.
Recent developments with baited traps include use of a pheromone (Rhynkolure) to attract the palm weevil to banana treated with insecticide (Cid del Prado, pers. communication). The combination of removal of infested plants and the use of pheromone traps is very effective.
For a list of plant species or cultivars (if any) reported to be immune or to have some level of resistance to this nematode species, copy the name
select Nemabase Resistance Search and paste the name in the Genus and species box
Baujard, P. 1989. Remarques sur les genres des sous-familles Bursaphelenchinae Paramonov, 1964 et Rhadinaphelenchinae Paramonov, 1964 (Nematoda: Aphelenchoididae.Revue de Nematologie12:323-324