Thielaviopsis paradoxa is the pathogen most commonly associated with Thielaviopsis trunk rot. A second pathogen associated with this disease is Thielaviopsis punctulata. Both pathogens belong to Kingdom Fungi, Phylum Ascomycota.
All palm species are considered potential hosts of Thielaviopsis paradoxa. The only known hosts of Thielaviopis punctulata are Cocos nucifera and Phoenix dactylifera.
Thielaviopsis paradoxa has a worldwide distribution. Thielaviopis punctulata appears to be limited to Kuwait, Mexico, South Africa and the USA (California only).
Thielaviopsis paradoxa degrades (rots) non-lignified or minimally lignified plant tissue. Thielaviopsis trunk rot is most often observed on mature palms with considerable trunk height. In the landscape, the trunk rot most often occurs in the upper half of the trunk or just below the apical meristem (bud) where there is less lignified trunk tissue. In palms with shorter trunks, which have less lignified tissue overall, the disease may occur anywhere on the trunk.
Unfortunately, there often are no visible indications that a palm has Thielaviopsis trunk rot until either the trunk collapses on itself (Figs. 1-3) or the canopy suddenly falls off the trunk. The canopy may appear relatively normal and healthy, as does the trunk externally. When the trunk collapse or canopy drop is observed, it means the fungus has rotted the trunk tissue to such an extent that the trunk can no longer structurally support itself. Examination of a cross-section through the diseased portion of the trunk will illustrate that the rot is located only on one side of the trunk (Fig. 4).
Visible symptoms that may be observed include wilting and necrosis of leaves (Fig. 5), beginning with the lowest leaves in the canopy. Darkened, very soft areas on the trunk may also be observed (Fig. 6), either associated with leaf wilt and necrosis or as an independent symptom. Push in with your fingers (or the blunt end of a small tool) on the suspected soft spot and then compare to other areas of the trunk (opposite side from soft area and further down on the trunk). If a trunk rot is present, you can easily push into the trunk an inch or more. In some cases, "stem bleeding" will occur, an oozing of plant liquid down the trunk that originates from the infection point (Fig. 7). Observation of these trunk symptoms is most likely on palms with smooth trunks, such as Cocos nucifera.
Fungal diseases: Ganoderma butt rot causes an internal rot of highly lignified tissue in the bottom 3 to 5 feet of the trunk. Ganoderma butt rot normally rots the trunk from the inside to the outside, whereas Thielaviopsis trunk rot destroys the trunk tissue from the outside to the inside.
Disorders: Lightning, bird damage, nail holes, and so on may cause physical damage to the trunk and cause the trunk to "bleed". However, the initiation point of the sap oozing due to these disorders will not be soft and rotted. Lightning may cause the quick collapse of the canopy or dislodge the canopy completely. Severe drought stress will cause wilt symptoms.