They fail to emerge normally, developing a downward hook and accordion leaf. The crown of the tree also bends to one side. Iron deficiency causes chlorosis which causes the fronds to become yellow or pale green.
The older fronds usually stay green but, if it is a recurring problem, the entire tree canopy can become pale yellow. Magnesium deficiency causes broad yellow bands on the leaflet edges. Nitrogen deficiency will cause the fronds to become pale green to pale yellow. The tree stops growing if this deficiency is not corrected and the trunk becomes tapered. Potassium deficiency causes yellow edges on the fronds and can cause them to look withered. Royal palms planted in soil with an alkaline pH over 7.
Ideally, the soil be should be acidic to neutral with a pH of 7. The soil should also drain quickly, although royal palms do fine if the soil stays wet occasionally. Give royal palms fertilizer specially formulated for palm trees.
Evergreen leaf-blades reaching 18 to 36 inches top a crown shaft that is long and green. Purple to black half-inch fruits are showy but not edible.
Growth Rate : Moderate. The Royal Palm can get up to 60 — 70ft tall and 5 ft wide with a growth rate of around a foot each year. This palm can be grown indoors if provided with enough light. Cold Tolerance : Roystonea oleracea can tolerate cold weather down to 30F for a short period of time. This palm is not cold hardy and needs to be protected from frost and cold snaps.
Light Req : Partial shade to Full sun. Water Req : Moderate. The Royal palm likes lots of water but it is moderately drought tolerant. This makes it a good tree even if you live in a place that has watering restrictions. While it does love to be watered, it must be well drained. Amazingly though, they not only tolerate, but seem to thrive in the poor soil and drainage of urban environments where other trees tend to do poorly.
The species is prone to potassium K , manganese Mn , and boron B deficiencies, especially on calcareous native or fill soils. Potassium deficiency symptoms in royal palms appears as leaflet tip necrosis and curling frizzling that is most severe on the oldest leaves Figure 3.
Potassium deficiency also causes premature leaf loss and reduces the number of leaves a palm can support. In severe cases of K deficiency, affected palms may have only a couple of stunted, off-color, and frizzled leaves. Such palms may also show a tapering of the trunk pencil-pointing , and they often die from the deficiency Figure 4. Symptoms of manganese deficiency can easily be confused with those of K deficiency, since both cause leaflet tip frizzling.
However, Mn deficiency symptoms appear on newly emerging leaves and are most severe toward the base of the leaf, while K deficiency symptoms are most severe toward the tips of the oldest leaves Figure 5.
Severely Mn-deficient royal palms may die if not treated with manganese sulfate. Boron deficiency causes stunting or distortion of newly emerging leaves, and in some cases, the entire crown may begin to grow sideways or even downwards Figure 6. Boron deficiency in royal palms can be fatal, but often is chronic. Regular fertilization with a controlled release fertilizer having an analysis of Mg or Mg plus micronutrients can correct and prevent nutrient deficiencies in these palms.
Royal palms have few serious insect pests, but one that is often severe and closely mimics K or Mn deficiencies is the royal palm bug Xylastodoris luteolus. This tiny, pale green, elongated bug infests newly emerging leaves as they unfold. Their feeding, primarily during the spring months, causes leaflets to appear chlorotic, then grayish-brown and frizzled Figure 7.
These leaves are typically frizzled throughout their length and are most apparent in mid-canopy leaves during mid-summer. This helps distinguishes royal palm bug damage from K and Mn deficiencies, which affect older and younger leaves, respectively. Compared to other palm species, royal palms are relatively disease resistant, being susceptible primarily to two trunk rotting fungal diseases. Ganoderma butt rot, caused by Ganoderma zonatum , infects the central portion of the bottom three feet of the trunk.
A cross section through the trunk will reveal discoloration of the decayed, but not soft, wood. The fruiting structure of the fungus, called a conk, may or may not appear on the outside of the lower trunk prior to palm death. Once a conk or wilt symptoms have been observed, the palm should be removed immediately as it could fall without warning and cause serious injury or property damage Figure 8.
Another lethal disease that is occasionally seen on royal palms is Thielaviopsis trunk rot. This fungus requires a wound in the upper, softer portion of the trunk for infection to occur. Pulling off leaves prematurely is one way to create such a wound. Once infection occurs, the fungus causes a wet soft rot through the trunk.
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