Not known to transmit any human or animal pathogens.

Not known to vector any pathogens or other associated organisms.

Rhynchophorus palmarum (South American palm weevil). Other Rhynchophorinae beetles, including Dynamis borassi and Metamasius hemipterus, are also reported to potentially vector the red ring nematode.

Samples should be sent to Dr. Tesfamariam Mengistu: 
Dr. Tesfamariam Mengistu
Mycology and Nematology Genetic Diversity and Biology Laboratory
USDA ARS Northeast Area
Bldg. 010A, Rm. 111, 118, BARC-West
10300 Baltimore Avenue
Beltsville, MD 20705, USA
Phone: 240-234-0284
Email: tesfamariam.mengistu@usda.gov

Two distinct types of symptoms are caused by B. cocophilus: red ring and little leaf. The specific symptoms for each disease are discussed separately below.

General symptoms

Infestations by B. cocophilus occur most commonly in trees that are 2.5 to 10 years old, with greatest incidence in those that are 4 to 7 years old. The first external symptoms are visible 1 to 2 months after inoculation. Symptomatic leaves become short, deformed, and turn yellowish-bronze before turning deep reddish-brown. The change in color typically starts at the leaf tip spreading towards the base, and leaves eventually wilt and die. Older leaves will show symptoms before younger leaves. As symptoms progress, the oldest leaves usually break at the petiole, close to the trunk, and can remain hanging down for a long period of time. In Cocos nucifera (coconut palm), premature fruit drop typically occurs at the same time or slightly before leaf symptoms develop. Four to six weeks after symptom development, the palm crown will often topple over; however, this is associated with severe internal damage caused by the larvae of the weevil vector. Therefore, this symptom may occur in the absence of the nematode.

Red ring symptoms

The nematode causes reddish lesions to form within the stem. These lesions gradually enlarge and often form a red ring when the cut stem is viewed in cross section, for which the disease was named. The ring can be ~1 to 2 in. wide, depending on tree size. The red ring typically occurs 14 to 21 days after inoculation with B. cocophilus and the color may vary from bright red to light pink, or cream to dark brown in Elaeis guineensis (African oil palm). The red ring can usually be seen when the infected palm is cut crosswise from 1 to 7 ft above the soil line, but it can appear anywhere along the trunk and may not be continuous throughout the infected palm. The ring may also be found in the cortex of the host roots and in the base of the palm fronds. When diseased, the soft, white cortex of the roots becomes orange to faint red in color and dry and flaky in texture.

Little leaf symptoms

Some African oil palms and older coconut palms will produce small, deformed leaves which remain green with no initial necrosis. Little leaf disease is a chronic condition that can lead to red ring disease development. These trees usually stop producing fruit. Nematodes can be found in high numbers in young leaves, when the leaves are elongating. These leaflets eventually become partially necrosed and remain partially folded along the rachis.

A Likelihood of Establishment Map is now available. This survey should only be considered in the states with appropriate conditions and suitable hosts for this pathogen. The map was produced by the SAFARIS Team. SAFARIS is a modeling framework that enables PPQ to quickly respond to emergencies, efficiently survey for pests, and assess potential pest impacts by collecting critical geospatial data and developing predictive models. SAFARIS is developed and maintained by the NC State University, Center for Integrated Pest Management (CIPM) with support from PPQ PPRA.

Surveys can occur year-round in areas with susceptible hosts.

Visually inspect palms throughout the survey site for external symptoms of red ring and little leaf diseases.

Survey for B. cocophilus in palm trees over 2 years old, especially in areas where Rhynchophorus palmarum (South American palm weevil) or other vectors are suspected or known to be present.

Host collection options: To obtain samples of nematodes from living trees: 

1. A stainless steel tube, sharpened at one end, is driven at an angle of 45° at the point selected for sampling. The tube needs to penetrate a minimum of 5 cm into the tree trunk. Multiple samples should be taken from an individual palm at 0.3 to 2.1 m (1 to 7 ft) above the soil line. 
2. An alternative method: Two holes, (15 cm) deep, can be drilled per tree, 6 in. (15 cm) from both ends using a 2.125 in. (5.4 cm) self-feeding wood bit using an electrical or 18-Volt-battery-powered drill. The wood shavings from the two trees are mixed together and a minimum 200 g of wood shavings are collected as one lab sample. Bore holes made with the tube should be sealed with silicone caulk because it is easy to control, inert, and creates a good seal to prevent the entry of weevils. Holes can also be filled with wooden dowels.
3. A method including nematode extraction: Cut transverse portions (discs) of infected coconut stems for nematode extraction. Chop stem fragments of red ring-diseased palms into small pieces. Both colored and discolored red ring-diseased tissues can be mixed. Place about 30 g of tissue per sample in a modified nematode extraction tray with a plastic net and paper tissue. Allow nematodes to migrate from plant tissue into the water overnight. Sieve each nematode suspension through 20 ?m pore size sieves, and individually handpick to Eppendorf tubes with DESS (dimethyl sulfoxide, disodium EDTA, and saturated NaCl) preserving solution for DNA extraction and molecular analysis.

Vector collection: Please follow the approved methods for Rhynchophorus palmarum to collect weevils. The PPQ identifier or state taxonomist can separate rinsate water from weevils to create suspect nematode samples.

The only other nematode known to cause severe damage in Cocos nucifera (coconut palm) is Radopholus similis (burrowing nematode). In coconut palms, R. similis causes non-specific general decline symptoms including stunting, yellowing, reduction in number and size of leaves and leaflets, delay in flowering, button shedding, and reduced yield. Infestation by R. similis produces small, elongate, orange-colored lesions on tender creamy-white roots.

External symptoms caused by B. cocophilus, particularly during the early stages of infestation, are similar to symptoms caused by various other pathogens or abiotic factors (e.g., nutrient deficiency or mechanical damage), and are thus rarely diagnostic.