Photographer: Society of Nematologists Slide Collection via UF/IFAS webpage Source: www.entomology.ifas.ufl.edu Copyright:UF/IFAS
Bursaphelenchus cocophilus nematodes infect palm trees and cause the red ring disease that is fatal to palm, coconut and other fruit trees. Chlorosis (leaf discoloration) first appears at the tips of the oldest leaves and spreads towards their bases .The brown lower leaves may break across the petiole of the lower part of the rachis, or they may become partly dislodged at the base and hang down. Nuts are shed prematurely, either simultaneously with the development of leaf symptoms, or slightly before. About 4-6 weeks after symptoms first appear the crown often topples over from the internal damage caused by the palm weevil larvae; but, the trunk remains standing in the field for several months until it decays. However, the outward yellow appearance of the nematode infection is sometimes indistinguishable from those of trees growing under conditions of poor drainage or during intense drought
The name Red Ring Disease comes from the internal lesions these nematodes cause and they appear as an orange to brick-red colored ring, 2-4 cm wide, and at a distance of 3-5 cm from the periphery. In longitudinal section, the reddened tissue may appear as two united bands joined in the bole forming a U-shape or full circle.
To view an adult Bursaphelenchus cocophilus click here
Bursaphelenchus cocophilus causes serious damage to coconut palms in the Neotropic region and also in Brazil where it is vectored by the weevil Rhincophorus palmarum. The nematode can be introduced with infected weevils or infected coconut palm material. There is a serious economic threat if the red ring disease comes to the United States; especially since it could then be vectored by native Rhincophorus cruentatus. If the nematode is able to utilize the native weevils it would expand the range of threat from just California and Texas, where the South American Palm Weevil is present, to all states where palm trees grow or are imported. This nematode poses a great risk to the ornamental palm industry of the U.S.
For more information on the South American Palm Weevil click here.
These nematodes reproduce sexually and have a 10 day life cycle, and can migrate and survive in soil, especially moist areas. This nematode can be transmitted by putting infected tissue in soil near healthy trees, but nematode survives free in soil only 3-4 days. Bursaphelenchus cocophilus adults are carried on body surface and also enter body through spiracles and mouth of the South American Palm Weevil (Rhynchophorus palmarum). 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.
The South American Palm Weevil was first identified in California in 2011. In June of 2012, the Texas AgriLife Extension and the federal agency APHIS detected the weevil in Alamo, Texas. It was thought to be brought in on an imported palm tree or an ornamental plant. The vector is present in the United States but there is no presence of Bursaphelenchus cocophilus yet.
Native Origin: Central and South America
U.S. Habitat: Highest incidence of red ring disease caused by Bursaphelenchus cocophilus occurs in low, poorly drained areas because this nematode is susceptible to desiccation; drought conditions keep the disease in check. Also, Bursaphelenchus cocophilus adults survive best in wet, swampy areas, in clay rather than sandy soil.
U.S. Present: South American Palm Weevils found in CA and TX are not yet infected with the nematode
In the Caribbean, Traps or guard baskets are designed to protect plantations from frequent outbreaks of Bursaphelenchus cocophilus. They do so by attracting and killing palm weevils which may enter the plantations from nearby diseased trees. Guard baskets are cylindrical, 1 m high and 0.3 m in diameter and are filled with chunks of fresh tissue from diseased coconut trees to attract the weevil.
There are no simple means of controlling this nematode and limited and expensive effective measures are available for control of it in living palms. Control is based on prevention rather than cure either by the destruction of infested palm material by cutting and burning, or by the injection of nematocides and burning, or by trapping and killing of the weevil vectors before they spread the nematodes.
Esser, R. and J. Meredith. 1987. Red ring nematode. Nemotology Circular of Florida Department of Agriculture No. 141. Gainesville, FL.
Gerber, K. and R. M. Giblin-Davis. 1990. Association of the red ring nematode, Rhadinaphelenchus cocophilus, and other nematode species with Rhynchophorus palmarum (Coleoptera: Curculionidae). J. Nematol. 22:143-149.
Griffith, R. 1987. Red ring disease of coconut palm. Plant Disease 71:193-196.
Hagley, E. A. 1963. The role of the palm weevil, Rhynchophorus palmarum, as a vector of red ring disease of coconuts. I. Results of preliminary investigations. Journal of Economic entomology, 56(3):375-380.