Palm Trees : Nurture, Trimming and Maintenance

The below text is taken from book "Your Florida Landscape" by Robert J. Black and Kathleen C. Ruppert. This book deals with everything that you need to know about types of palms in Florida, Palm plant care and how to take care of them, Palm tree trimming, Palm tree nutritional guide, Palm tree pruning, Palm tree fertilizers, how to cut and kill the root of a palm tree and many more.

PALM NUTRITION GUIDE

Palms are among the most important ornamental plants in Florida landscapes and will suffer quickly and conspicuously from improper mineral nutrition.  Compared to other ornamentals, palms may exhibit certain of their nutritional disorders in unique ways.

Some nutritional problems in palms are difficult to diagnose accurately because symptoms of several different mineral deficiencies may overlap.  In this guide, nutritional disorders common to pals growing both in the landscape and in containers are discussed and illustrated.  Fertilization recommendation are also provided.

Nutritional Disorders in the Landscape

Nitrogen

Nitrogen deficiency is fairly common in Florida palms, although deficiencies of elements such as potassium, magnesium and manganese are much more prevalent and serious. Symptoms of nitrogen deficiency include an overall light green color and decreased vigor of the palm (Plate 3). Correct by applying any nitrogen fertilizer to the soil.

Potassium

Potassium deficiency is perhaps the most widespread and serious of all disorders in Florida palms.  Symptoms occur first on the oldest leaves and appear on progressively newer leaves as the deficiency become more severe.  Symptoms vary among palm species but typically begin as translucent yellow or orange spots on the leaflets (Plate 4).  These may or may not be accompanied by necrotic spots, which are areas of dead tissue.  Leaflets will typically have areas of necrosis along the margins (Plate 5).  As the symptoms progress, the leaflet or entire leaves will become withered or frizzled in appearance (Plate 6).  The midrib usually remains alive on potassium deficient leave, although it may be orange in color instead of green in some species.  In date palms (Phoenix spp), symptoms are slightly different in that older leaves show an orange-brown discoloration near the tip (Plate 7).  Also, the leaflet tips, rather than the margins, become necrotic as the deficiency progresses.  The color of the chlorotic (i.e, yellowing) region in Phoenix leaves is a dull orange or even tan (Plate 7) in comparison to the bright yellow of a magnesium deficiency (Plate 8).

Potassium is moved from older to new leaves as required by the palm.  In severe deficiencies, the canopy will be greatly reduced in size due to the removal of potassium from all of the leaves. Once all potassium has been removed from older leaves, the palm will go into a state of decline.  With reduced trunk diameter (penal-pointing) and the emergence of small, frizzed or chlorotic new leaves. Without prompt treatment the palm will usually die.  Potassium deficiency affects all species of palms but is most severe in royal, queen, coconut, areas and spindle palms.  Treatment required soil applications of sulfur – or resin-coated potassium sulfate at rates of 2 to 5 lbs per tree four times per year plus half as much magnesium sulfate to prevent a potassium-magnesium imbalance and resulting magnesium deficiency.  Symptomatic leaves on potassium deficiency.  Symptomatic leaves on potassium deficient palms will never recover and must be replaced by new, healthy leaves.  In severely deficient palms, this means replacement of the entire canopy which may take 2 years or longer.  Foliar sprays with potassium fertilizers are ineffective in correcting the problems since the amount of potassium supplied by a foliar spray is insignificant compared by a foliar spray is insignificant compared to the amount needed to correct the problems.

Magnesium

Magnesium deficiency is also quite common in Florida palms, but especially in Phoenix species.  As with a potassium deficiency, symptoms occur first on the oldest leaves and progress up through the canopy.  Typical symptoms are a broad light-yellow band along the margin of the older leaves with the center of the leaf remaining distinctively green (Plate 8).  In severe cases, leaflet tips may become necrotic, but a magnesium deficiency is rarely, if ever, fatal to palms.

Magnesium deficiency is best treated preventatively since treatment of deficient palm takes considerable time.  As with a potassium deficiency, symptomatic leaves will never recover and must be replaced by new healthy leaves.  Applications of magnesium sulfate at rates of 1 to 3 lbs per tree four times per years plus coated potassium sulfate at the same rate should correct the problem and prevent the occurrence of a potassium-magnesium imbalance.

Manganese

Manganese deficiency or ‘frizzle top’ is a common problem in palms growing in the alkaline soils that cover much of south Florida.  Symptoms occur only on new leave which emerge chlorotic, weak, reduced in size and with extensive necrotic streaking in the leaves (Plate 9). As the deficiency progresses, succeeding leaves will emerge completely withered frizzled or scorched in appearance and greatly reduced in size (Plate 10 and 11).  Later only necrotic petiole stubs will emerge, and death of the bud quickly follows.

Manganese deficiency is primarily caused by the element’s insolubility at high pHs.  In some palms such as coconut, which are not normally affected by the problems, cold soil temperatures during the winter and spring months reduce root activity and thus the uptake of micronutrients (especially manganese). Coconut palms that are severely deficiency in manganese during the winter and spring will usually grow out of the problem without special treatment once soil temperatures warm up in late spring.  Other palms such as queen, royal, Paurotis and pygmy date palms are highly susceptible to manganese deficiency and must be treated with soil or foliar applications of manganese with soil or foliar application of manganese sulfate or they will likely die.

Iron

Iron deficiency is relatively uncommon in landscape palm and is not usually caused by a lack of iron in the soil or even by high soil pH as is the case with many other plants.  Iron deficiency usually appear in palms.  Iron deficiency usually appear in palms that are growing in poorly aerated soil or that have been planted too deeply.  Waterlogged soils and deep planting effectively suffocate the roots.  Symptoms appear first on the new leaves and in most palms consist of uniformly chlorotic new leaves (Plant 12).  As the deficiency progresses, new leaves will show extensive necrosis and reduced leaf size.  Early symptoms in queen palms include pea-sized green spots on otherwise yellowish new leaves (Plate 13).

Iron deficiency symptoms can sometimes be temporarily alleviated by regular foliar applications of iron sulfate or chelates, but long-term correction will only occur when the poor soil aeration or improper planting depth that caused the deficiency is corrected.

 

Diagnosis of nutrient deficiencies by visual symptoms alone can be difficult since some of the symptoms overlap considerably in some species.  For instance, manganese and later stage potassium deficiencies are easily confused on queen ad royal palms.  Potassium and magnesium deficiencies are very similar in pygmy date palms.  Late stage potassium and iron deficiencies can be accent specimens, tall solitary palms make effective border or boundary plantings for lining a long driveway or boulevard.  Such tall growing palms as the royal palm (Roystonea spp.)  Provide a strong vertical accent in the landscape but can overpower a small building and make it appear even smaller.

Palms can be planted in combination with each other as well as with other types of landscape plants.  A well-designed bed of various palm species can be the focal point of a subtropical landscape.  Growth rates, habit and eventual size must be considered carefully when combining species to avoid a halter smelter mix that fails aesthetically.

Small groves of the same species can create an attractive landscape accent.  King Alexander (Archontophoenix Alexandrea), queen palms (Syagrus romanzoffiana), various Veitchla species and many other slender or moderate trunked species can be grouped successfully in the landscape.  Densely clustering species such as the lady palms (Rhapis spp.), some Chamaedorea species and area (Chrysaidocarpus lutescens) can be used to create a screen.

Avoid planting tall growing palms directly under roof overhangs and eaves.  A misplaced palm will one day have to be removed.

Pruning Palms

Palms do not require the same kind of pruning as branching, broad-leaved tree.  The only trimming any palm needs is removal of dead or badly damaged or diseased leaves.  Some landscape maintenance workers have an unfortunate tendency to over trim palm, removing perfectly good green leaves along with the dead or dying fronds.  No doubt the reason for this practice is an attempt to lengthen the interval before trimming is once again necessary, but the removal of healthy leaves is a disservice to the palm, especially those species whose canopy consists of no more than eight to twelve leaves.  Out of fear that palm fronds could become projectiles in a storm, removal of healthy lower leaves is sometimes carried out as a safety measure.  However, by this logic, the limbs of broad-leaved trees also pose a threat and require removal.  Such precautions are obviously too extreme.  Over trimming reduces the food manufacturing efficiency of the living palm and can result in suboptimum development of the trunk diameter at the point in the crown where diameter increase is currently taking place.  There is also some evidence that over trimming makes the palm more susceptible to cold damage.  Do not permit the use of climbing spikes on your palms as palms lack the ability to produce callus to cover wounds.  Any holes in the trunk, including those cause by spikes, can lead to disease problems.

There is no evidence to indicate that a palm will grow better or worse if the boots (old leaf bases) are removed.  The boots do provide protection and insulation from cold damages, fire and other natural calamities.  Sometimes, too, trunk tissue can be stripped off when a boot is removed before it is ready.  Care should be taken to avoid causing such damage.  Growing ferns in the “pockets” created by boots, though aesthetically pleasing, can trap moisture close to the trunk and create a potential for fungus and vermin in the crown.

PESTS & OTHER PROBLEMS OF PALMS

Insect and Mite Problems

We are fortunate indeed that, relative to most landscape plants, a well-grown palm remains fairly free of damaging insect pests.  Nevertheless, certain insects will occasionally attack landscape palms in sufficient fore to warrant control measure.

Palm aphid (Cerataphis palmae). This aphid is unusual in that the female does not move and forms a distinctive ring of white wax around its body (Plate 14). These aphids heavily infest young leaves and excrete honeydew upon which black sooty mold will grow.  They are sometimes tended by ants.  Lady beetles are an excellent biological control, and spraying should be avoiding if these aphid predators are observed on the infested palm.

Scales. In great variety, do turn up on palm leaves from time to time and include thread scale, magnolia white scale, oyster scale, Florida red scale and others.  The hard shell of many scales reduces the effectiveness of many chemicals.  Scales are more frequently a nuisance than a menace to palms. On a landscape size specimen, the most effective control for an infestation on a single leaf is removal.

Spider mites. Spider mites are particularly troublesome on palms grown indoors or in greenhouses and also on many Chamaedorea Species.  The predatory mite species, Phytoseiulus persimilis has been used very successfully to control two-spotted mites (Tetranychus urticae) on palms in the greenhouse and other interior environment.  Many chemical miticides work successfully too.

Coconut mite. This tiny spider mite feeds on the husk of coconut fruits, causing mostly cosmetic damage (Plate 15) but sometimes premature fruit drop as well.  There is no known control for the coconut mite.

Banana moth (Opogona saccharl). The larvae of this moth have been a destructive pest in tropical areas on palm species such as Chamaedorea, arecas and others.  Though it is more commonly a palm production pest, infestations of landscapes palms have occurred.  Damage occurs when the caterpillar tunnels through the stems of the palms.  Parasitic nematodes have been fairly effective in controlling infestations of this insect.

Palm leaf skeletonizer (Homaledra sabalella). The caterpillars of this small moth feed on the upper and lower leaf surfaces of many palms, producing large qualities of ‘frass’ (brown fibrous excrement) that is often the first conspicuous sign of an infestation. The tissue between the veins or ribs is usually their preferred food (Plate 100), but they will also feed on the leaf steams, disrupting the vascular tissue and causing the death of the entire leaf.

Royal palm bug Xylastodoris luteolys, Plate 16) is a troublesome pest of royal palms (Roystonea spp.)  in Florida and the Caribbean.  Infestations in South Florida tend to increase in the spring and summer following a particularly mild winter.  This tiny bug feeds on the young leaves of the palms (Plate 17), often getting in between the folds of an emerging leaf.  When the leaf unfolds it appears scorched and brown and usually fails to mature.

Palmetto weevils (Rynchophorus cruentatus) are large bee ties that are drawn to stresses palm (Plate 18).  They most frequently attack cabbage palms (Sabal palmetto) and Canary Island date palms (Phoenix Canariensis), but have been reported on Mexican fan palms (Washingtonian Robusta), Bismarck palms (Bismarck IA nobilis), and latan Palms (Latania spp.). Adult females lay eggs in the leaf bases of the crown, and the large larvae (Plate 19) quickly tunnel into the heart, destroying the palm (Plate 20).  All efforts should be made to reduce transplant stress on susceptible species.  A preventative spray of a recommended insecticide, applied at installation and again a few weeks later, has shown some success in keeping palms free of infestation. A related species of weevil, R. palmarum, occurs in Central and south America and the Caribbean and spreads a destructive nematode that causes red ring disease in coconuts ad African oil palms.

Rotten sugar can borer (Metamasium Hemipterus) is a relatively new pest of palms in south Florida.  It attacks royal palms (Roystonea spp.), majesty palm (Ravenea Rivularis), spindle palm (Hyophorbe verschaffeltii), Mexican fan palm (Washingtonia Robusta) and possibly others.  The larvae of this weevil completely riddle the stems of the palms which then succumb to various secondary disease organisms.

Various caterpillars and some grasshoppers feed on the leaves of palms from time to time.  Small infestation can be dealt with mechanically without recourse to pesticides.  If, however, these insects are on palm foliage in force, they can very quickly do appetible damage, completely defoliating a young palm in as little as 1 to 2 days.

Disease Problems

Leaf Spots. A number of leaf spot fungi causes variously shaped lesions on the leaf surface of many palm species.  High rainfall or frequent overhead irrigation are often instrumental in their spread.  If only a single leaf is affected, removal and disposal of that leaf is a simple and effective control.  Some leaf fungi move in as secondary problems on palm leaves that are deficient in nutrients or have received some sort of damage.

Leaf spot diseases caused by various Bipolaris and Exserohilum fungi (often called Helminthosporium-complex leaf spots) affect a broad range of palms.  The results are characteristically round, dark brown lesions (Plate 21) that eventually merge and form large blighted areas.  The disease is easily spread by overhead irrigation.  Cercospora leaf spot is frequently a problem on Rhapis palms and Cylindricladium on lcentia (Howea Forsterana).  Anthracnose caused by a Collectotirchum fungus can affect a large number of palms, especially where overhead irrigation is used. Stigmina (Exosporium fungus) leaf spot can be a particular problem on date palm (Phoenix) species, Graphlola leaf spot or ‘false smut’ can become significant problem on landscape palms during periods of high rainfall.  The disease becomes conspicuous when the fungus produces its grayish-black fruiting bodies which rupture through both leaf surfaces (Plate 22). Pestalotiopsis leaf spot affects a number of species.  It seems to be a particular problem on the date palm (Phoenix) species on which lesions often first appear on the rachis tissue (the leaf stem between the leaflets.)  Tar spot (Catacauma leaf spot) causes elongated, diamond-shaped lesions on the leaf surface.

Sooty mold. This superficial fungus, caused by Capnodium spp., is more a nuisance than a life-or-death problem on palms.  When present, it is always associated with infestations of sucking insects such as palm aphid, scales, or mealybugs.  These insects excrete ‘honeydew’ a water product high in sugars that the sooty mold fungus feed upon.  The fungus appears on the leaf surface (and sometimes the trunk) as a conspicuous black, sooty deposit (plate 162). Heavy infestation will interfere with the food manufacturing efficiency of the leaf.  The best control is to keep the palm tree of honeydew producing insects.

Bud, Root or Trunk Rots and Wilts

Phytophthora bud rot is one of the more common disease encountered in palms in wet tropical climates. It is primarily a warm season disease. This soil-borne disease cause collapse or brown-out of the younger foliage and emerging leaf. If the bud is cut open, discoloration is evident (plate 23) often accompanied by a foul smell. Phytophthora can also cause leaf spots. Over watering and planting too deeply aggravate incidences of Phytophthora. Pythium and Rhizoctonia root rots can also affect palms.

Thielavlopsis trunk or bud rot is increasing in frequency on palms in Florida but is not yet terribly common. This soil-borne fungus generally enters the palm through wounds and causes the disintegration of the trunk or bud. It can also infect the leaves of young Palms. A cross-section through the trunk will reveal blackened fruiting bodies. Affected palms will blow over easily.

Ganoderma butt rot has become a serious and incurable disease of older landscape palms (usually 15 years or older) the disease progresses upward from the older leaves, which turn brown and droop from the trunk. wounds on the lower portions of the trunk or roots favor entry of the fungus. The fruiting body of the fungus is a conspicuous bracket or “conch” found emerging from the lower portions of the trunk(plate24). These fruiting bodies should be destroyed as soon as they appear by either burning them or breaking them up and tossing the pieces into chlorine bleach. The disease spreads rapidly from plant to plant, and the fungus can persist in the soil from many years. affected palms must be completely removed and destroyed and the soil fertigated. Affected palm steams should not be chipped and used as much.

Poor air circulation around the base of the palm trunk or frequent wetting of the trunk by sprinklers may also increase susceptibly to Ganoderma. Avoid mounding much at inches back from the trunk. Make sure line trimmers and other lawn care equipment do not damage the trunks of palms planted in turf. If Ganoderma has been diagnosed in a landscape site, It may be best to replant with a board-leaved tree as no palm species can yet be declared reliably resistant.

Fusarium bud rot and wilt, more common a problem in California, may become a serious disease in Florida.  The disease frequently causes in uneven decline in the canopy of an infected palm, with leaflet along only one side of a single leaf dying first.  The water and food conducting tissue within the leaves is usually discolored.  Canary Island a date palms have been the worst affected in California.  Pruning tools are known to transfer the fungus from tree to tree and should be sterilized before using on a different tree.  Dip tools into rubbing alcohol for 30 seconds before each re-use to kill this harmful fungus.

Bacterial bud root causes a wet blight of the emerging spear leaf which can then spread downward to the irreplaceable bud.  Affected spear leaves can often be easily pulled from the bud.  A foul odor frequently accompanies the damage.  Bacterial bud rot often follows hard on the heel of recent cold damage to a palm.

Lethal Yellowing (LY) is an incurable disease of many palm species caused by a mycroplasama like organism (a form o life sometimes described as intermediate between a virus and a bacterium) that is spread by a leaf hopper bug (Myndus crudus).  Fortunately, the popular cabbage palm, Florida’s state tree, as so far proven resistant to the disease.  The disease organism is now known to reside in the Florida countries of Palm Beach, Broward, Dade, Monroe, Lee and Collier as well as in southern Texas, Mexico and part of Africa. The disease often begins with the blackening of young flower stems on infected palm.  On coconuts, developing fruits will suddenly drop off the stems.  One by one, mature leaves may begin to yellow on the palm and finally all the leaves in the canopy wit and die (Plate 25).  ON other species (and some varieties of coconut as well) the yellowing may not be conspicuous; instead, leaves collapse and the palm quickly dies. The only practical control is to avoid planting highly LY-susceptible palms (table 10).  The decline caused by the disease can be temporarily suspended (though not cured) with a program of injections of tetracycline antibiotics (but only on palms with a developed trunk).  Contact your country Extension agent for further information.  Injections can be maintained until a resistant replacement palm achieves acceptable size, after which the infected palm is allowed to die.

Miscellaneous Palm Problems

Landscape palm occasionally experience other problems that are not necessarily the consequences of pests, disease or nutritional deficiency.

Trunk splits or cracks. Some palm species (e.g., hurricane palm, dictyosperma album) characteristically develop vertical fissures on their trunks.  When these appear on palms normally do not express them, it is usually an indication of water problems.  Too much or too little soil moisture can result in small cracks on the trunk as can overly deep planting.  Large scale trunk splitting is often associated with an over-abundance of water (Plate 26).  Trunk cracking can also occur as a consequence of cold damage.

Trunk constrictions. AT the point in the palm heart (bud) where active growth is taking place.  Palm steams increase in diameter before elongating.  The optimal trunk diameter that a palm species will achieve is partially determined by the intrinsic character of the species and partially by the quality of the growing conditions at that point in time.  If nutrition or water supply is limiting or if some other type of environment stress occurs (a freeze, for example), the palm stem may fail to achieve the same increase in diameter as occurred in past years.  As conditions improve, the stem will once again reach optimum trunk diameter.  The result over the long term will be a constriction in he trunk at the point where the stem was actively growing when the stresses occurred. In older palm, it is sometimes possible to read the past history of growing conditions by the patterns of constrictions that appear along the length of the trunk.

Pencil-pointing. This syndrome is often related to that trunk constriction.  ‘Pencil pointing’ refers to a sudden, unnatural narrowing of the stem towards the crown of the palm.  It is often associated with acute nutrient deficiencies but can also be caused by continuous over-trimming of the canopy.  If conditions improve, the palm will return to its normal growth in trunk diameter, and a trunk constriction will develop at the point where pencil-pointing was observed.

Lightning strike (Plate 27). A direct lightning hit on a palm is usually fatal.  Sudden collapse of the crown, trunk splitting and/or bleeding and dark streaks on the trunk are all possible symptoms of lightning damages.

Power line decline. Tall palms that have grown close to high voltage power lines have been observed to have yellowed or necrotic leaves despite regular fertilization and no evidence of pests or disease.  This suggests that the electromagnetic fields around these lines may injure palms.

Herbicide toxicity. Many herbicides can cause damage to palms. Signs of herbicide injury include distorted and under-sized new growth and patches of dead tissue on the leaves.  Damage from some herbicides may take months to become apparent.  Consequently, special care should be taken when using weed-killing chemicals around landscape palms.  Avid and contact of the chemical with new roots or any green tissue on the palm.  Only herbicides labeled for use around palm should be applied.

After flower decline. Certain palms species (e.g. fishtail palms, Caryota spp.) flower and fruit once and then die.  On clustering species with this habit, new stems are produced that continue the growth of the palms, but solitary palms will have to be replaced.

Salt injury. Leaf burn on the seaward side of palms planted near the shore is often indicative of salt injury.  Such injury usually follows a period of high winds.  A sudden intrusion of salt water into the root zone of palms can cause an overall decline and death of the plant.  The best way to deal with the problems is to plant only those palms with high salt tolerance in expose coastal locations.

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