Two distinct types of symptoms are caused by B. cocophilus : "red ring" and "little leaf disease".
The nematode causes reddish lesions to form in the stem. These lesions gradually enlarge and often form the primary and most characteristic internal symptom of the disease for which the disease was named, a "red ring" when the cut stem is viewed in cross section. The ring may vary in color from bright red to light pink, or cream to dark brown in Elaeis guineensis (African oil palm). The ring can be 3 to 5 cm wide (1.18 to 1.97 in) from the periphery, but the width may vary depending on tree size. The red ring can usually be seen when the infected palm is cut crosswise from 0.3 to 2.1 meters (1 to 7 ft.) above the soil line. The ring may not be continuous throughout the trunk length. The ring may also be found in the cortex of the host roots and in the petioles. When diseased, the soft, white cortex of the roots becomes orange to faint red in color and dry and flaky in texture.
With red ring disease, established leaves become short, deformed, and turn yellowish-bronze before turning deep reddish-brown in color. The change in color typically starts at the leaf tip spreading towards the base. Older leaves will show symptoms before younger leaves. Leaves will eventually wilt and die. The oldest leaves usually break at the petiole, close to the trunk and can remain hanging down for a long period of time. In coconut palm (Cocos nucifera), fruit typically drop prematurely (before mature). This usually happens around the same time that leaf symptoms develop or slightly before. Four to six weeks after symptom development, the palm crown will often topple over; this is associated with severe internal damage caused by the larvae of the weevil vector.
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.