No specific name can be assigned to a particular bud rot until after the pathogen is determined.
Gliocladium vermoeseni (=Nalanthamala vermoeseni): Kingdom Fungi, Imperfect Fungi (no known sexual state)
Phytophthora palmivora, Phytophthora katsurae: Kingdom Stramenopila, Phylum Oomycota
Thielaviopsis paradoxa: Kingdom Fungi, Phylum Ascomycota
All palms are considered susceptible to at least one of the bud rot pathogens.
Phytophthora palmivora has a worldwide distribution and is probably the most common bud rot pathogen in the continental United States and Caribbean region, but Phytophthora katsurae is just as common in Hawaii.
Gliocladium vermoeseni is an opportunistic pathogen with a worldwide distribution that is more likely to be observed in cooler climates (e.g., coastal California) or cooler seasons of the year (e.g., winter months in Florida).
Thielaviopsis paradoxa, which has a worldwide distribution, is reported in the literature as a cause of bud rot, but it is not clear how often this pathogen causes this disease.
The first symptom of a bud rot is the discoloration and possibly a wilting of the spear leaf (youngest, unopened leaf) (Fig. 1). The next youngest leaves may also appear discolored (chlorotic or necrotic) and wilted. Eventually, the spear leaf (and sometimes the next youngest leaves) becomes desiccated, necrotic and collapses (Figs. 2-4). A close examination of the leaves prior to complete desiccation and collapse, especially the spear leaf, often reveals blighted areas on the unopened leaf blade (Fig. 5). As the disease progresses into the bud (heart or apical meristem), this tissue rots and the spear leaf can be easily pulled from the bud. This rot is normally associated with a very foul odor. The rest of the leaves in the canopy will appear healthy; it is only the spear leaf, the surrounding youngest leaves and bud that are affected.
No new leaves emerge from the bud because the apical meristem is either rotted or no longer functioning as meristematic tissue. However, the leaves that were already present prior to bud infection will remain green, appear healthy and remain attached to the trunk (Figs. 3 and 6). Eventually, these leaves will go from green to various shades of yellow and brown, but this is due to natural senescence or secondary leaf diseases and is not due to the bud rot disease.
If the diseased palm is still in a container or small enough in the field or landscape that the top of the canopy is still at eye level or below, the wilting and discoloration of the youngest leaves will be the first symptoms observed. However, if the palm is so tall that the canopy is above eye level, then the first symptom observed is usually a missing spear leaf, the lack of new leaves emerging, or an open-topped crown (Fig. 6). The diseased palm did go through the discoloration, wilting and death of the youngest leaves, but that symptom was missed because the palm was too tall for easy viewing of these leaves.
In Hawaii, where bud rot of Cocos nucifera is caused by Phytophthora katsurae, another early symptom of bud rot is premature loss of fruits. The nuts develop distinctive large, brown lesions with green circles within these lesions (Fig. 7).
If the bud rot is caused by Gliocladium vermoeseni, then a mass of pink-orange or pink salmon colored spores is usually evident on the affected tissue (Fig. 8).
In some cases, disease development may cease prior to death of the bud. In these situations, the palm may recover, but the first few new leaves that emerge usually appear abnormal - smaller in size, distorted shape, etc.
One of the symptoms of lethal yellowing or Texas Phoenix palm decline in Phoenix spp., Sabal palmetto, and Syagrus romanzoffiana is death of the spear leaf. However, prior to death of the spear leaf, you would observe early fruit drop, necrosis of the inflorescenses, and necrosis of about 25% of the lowest leaves in the canopy. You would not observe these symptoms in these species if the palms are affected by bud rot.
Cold damage to the bud (apical meristem) often results in a bud rot due to opportunistic pathogens (various fungi and bacteria) invading the damaged bud tissue. This bud rot is often not readily apparent for many weeks or even months after the cold damage occurred. There is a wide range of cold tolerance within the palm family. Also, palm species that might be tolerant of cold weather as mature specimens with elongated woody trunks and a full canopy may not be tolerant of the same weather event if the same palm species is a seedling, a juvenile, has a very short trunk or has had an excessive number of leaves removed.