Texas Phoenix Palm Decline
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Figure 2. This Phoenix sylvestris has one necrotic older leaf and three other older leaves with initial leaf symptoms - brief yellowing period followed by complete necrosis. Photo by M. L. Elliott.
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Figure 1. This Phoenix dactylifera dropped almost all of its fruit in just 2 to 3 days. Photo by M. L. Elliott.
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Figure 4. Phoenix sylvestris with significantly more dead leaves than would be normal. Note the reddish-brown coloration of the leaves.Photo by B. Dick, City of Lakeland, Florida.
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Figure 3. The Phoenix canariensis in the center and on the right have more dead leaves than would be normal, and are in contrast to the healthy palm on the left. Photo by M. L. Elliott.
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Figure 6. The spear leaf has died and is hanging down below the canopy of this Phoenix sylvestris. Photo by M. L. Elliott.
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Figure 5. The second Phoenix dactylifera from the right has more dead leaves than the remaining healthy palms. Photo by B. Dick, City of Lakeland, Florida.
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Figure 8. Sabal palmetto with two-thirds of the lower leaves necrotic and a dead spear leaf. Note that the next youngest leaves are still green. Photo by N. A. Harrison, University of Florida.
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Figure 7. This photograph illustrates both a dying spear leaf and fruit stalks that have lost all of their fruit. Photo by M. L. Elliott.
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Other common names
date palm lethal decline, Texas Phoenix decline
Scientific name of pathogen
‘Candidatus Phytoplasma palmae’ subgroup 16SrIV, strain D: Kingdom Bacteria, Division Firmicutes
Hosts
Phoenix canariensis, Phoenix dactylifera, Phoenix reclinata, Phoenix roebelenii, Phoenix sylvestris, Pseudopheoenix sargentii, Sabal mexicana, Sabal palmetto, Syagrus romanzoffiana, Thrinax radiata
Distribution
Mexico (Yucatan), USA (Florida and Texas). In Florida, the pathogen has been detected in Broward, DeSoto, Hardee, Highlands, Hillsborough, Indian River, Manatee, Orange, Palm Beach, Pasco, Pinellas, Polk, Sarasota, and Sumter counties. In Texas, the disease has been confirmed in Bexar, Cameron, Hidalgo, Kleberg, Nueces, Tarrant, and Willacy counties.
Symptoms/signs
Field diagnosis is based on a series of symptoms. No single symptom is diagnostic of Texas Phoenix palm decline. Rather, it is the appearance and chronological progression of symptoms that accurately identifies the disease.
The first obvious symptom of Texas Phoenix palm decline on mature palms is premature drop of most or all fruits and inflorescence necrosisnecrosis:
dead tissue, usually desiccated and brown to gray in color
. The fruit drop occurs within a few days; it is not spread out over a prolonged period of time (Fig. 1). However, these two symptoms will only be observed if the palm is mature enough to produce fruit, if it is the season for flowering and fruiting, and if the flowers or fruits have not been trimmed from the palm.
The next symptom is discoloration of the foliage, beginning with the oldest leaves. The discoloration begins at leaf tips. While portions of the leaf turn yellow, they do not remain yellow for very long. Instead, the leaves quickly turn varying shades of reddish-brown to dark brown or gray (Fig. 2). Unless the palm is being monitored closely, the onset of leaf discoloration is usually first recognized as a greater number of dead older leaves than is normal for natural senescence (Figs. 3-5). However, if the dying or dead leaves are being regularly removed, even this symptom of foliage discoloration may not be obvious
Death of the spear leafspear leaf:
the younges emerging leaf that has not yet opened
is the next symptom observed. This appears to occur quite early in the disease process for Phoenix spp. (less than 1/3 of the leaves are discolored or necroticnecrotic:
see necrosis
(Fig. 6 and 7), but later in the process for Sabal palmetto (2/3 of the leaves are discolored or necroticnecrotic:
see necrosis
) (Fig. 8).
Once the spear leafspear leaf:
the younges emerging leaf that has not yet opened
has died, no new leaves will develop, and the remaining leaves will continue to become discolored or necroticnecrotic:
see necrosis
from the oldest to the youngest leaves. In some instances, by the time the spear leafspear leaf:
the younges emerging leaf that has not yet opened
dies, palm roots at or near the soil surface are soft in texture and easily broken. Such palms can be easily rocked back and forth in the ground because the root system is decaying.
May be confused with
Phytoplasma diseases: Lethal yellowing causes the same symptoms as Texas Phoenix palm decline in Phoenix species. It would not be possible to determine which pathogen was affecting the palm without the proper molecular diagnostic test.
Fungal diseases: Ganoderma butt rot will cause lower leaves in the canopycanopy:
the cluster of leaves borne at the tip of the stem
to die prematurely or cause an overall wilt of the canopycanopy:
the cluster of leaves borne at the tip of the stem
, but it will not cause premature death of the spear leafspear leaf:
the younges emerging leaf that has not yet opened
. Budbud:
a common term for meristem; the specialized growing region of a plant containing undifferentiated cells from which new cells and organs are developed
rot causes premature death of the spear leafspear leaf:
the younges emerging leaf that has not yet opened
, but will not cause premature death of the lowest leaves.
Disorders: Potassium deficiency will cause discoloration and premature death of the lowest leaves, but does not cause premature death of the spear leafspear leaf:
the younges emerging leaf that has not yet opened
or fruit drop.
Additional comments
Death of the spear leafspear leaf:
the younges emerging leaf that has not yet opened
may not always be obvious. Both Phoenix species and Sabal palmetto have numerous young leaves surrounding the spear leafspear leaf:
the younges emerging leaf that has not yet opened
. Unless you see the spear leafspear leaf:
the younges emerging leaf that has not yet opened
is dead or find it hanging from the canopycanopy:
the cluster of leaves borne at the tip of the stem
or on the ground, you will probably need to physically examine the canopycanopy:
the cluster of leaves borne at the tip of the stem
closely to determine whether a healthy spear leafspear leaf:
the younges emerging leaf that has not yet opened
is present. Also, the young spear leafspear leaf:
the younges emerging leaf that has not yet opened
of a healthy Phoenix species is enclosed in a thin, brown sheath (which tears like paper). Be careful not to confuse the normally occurring brown sheath for a dead spear leafspear leaf:
the younges emerging leaf that has not yet opened
.
