Solve the Worst

Solve the Worst Palm Problems Identify and treat problems alms are an important of the leaf, progressing along one side of the | component of the land- leaf to its tip and back down the other side in palms before they become scape in areas having to its base. Once the majority of leaves in serious because the cost of mild climates. They im- the canopy have died, the remaining green part a distinctly tropical leaves will wilt and the bud will die. Unfor- producing and installing large look that few other plants can provide. tunately, there are no effective chemical specimen palms can be high Unfortunately, because most palms have controls for this disease and reducing the only a single terminal bud or rate of spread to healthy growing point, diseases or palms is the best strategy. By TIMOTHY K. physiological disorders that Fusarium oxysporum f. BROSCHAT, Ph.D. might merely weaken sp. canariensis can sur- broadleaf trees are often fatal vive for years in the soil in palms. and can readily infect new replacement palms. 1) Fusarium Wilt Similarly, transplanted One of the most serious field-grown palms from diseases of Canary Island date infested fields can spread palms in California, and more this disease. However, recently Florida, is Fusarium the primary means of wilt. It is characterized by spread is via contami- death of the leaflets on one nated pruning tools. side of an older leaf or the Infected palms should leaves on just one side of the only be trimmed once crown. Symptoms typically per year to minimize begin on leaflets near the base spread, and all tools used should be disinfected be- • 1) Fusarium wilt of Canary Island date palm. fore moving on to the next palm. Research at the University of (Roystonea spp.), sabal palms (Sabal spp.), spores capable of infecting dead palm Florida has shown that soaking tools for 10 queen palm (Syagrus romanzoffiana), and wood or healthy palms some distance from minutes in 25% chlorine bleach, 50% iso- Washington palms (Washingtonia spp.). the point of release. Although mechanical propyl or denatured alcohol, or 25% Pine- wounding of palm trunks increases the Sol disinfectant are all effective in eliminat- 3) Ganoderma Butt Rot likelihood of infection, wounding is not ing this fungus from pruning equipment. Ganoderma butt rot is probably the necessary for infection to occur. When pruning, avoid cutting into green most devastating palm disease in the south- Ganoderma zonatum, the causal organ- leaf bases. eastern United States. Its range corre- ism, can also spread through the soil, living sponds roughly with that of the sabal palm on dead palm roots and wood. One of the 2) Lethal Yellowing [Sabal palmetto) and extends from South most common means by which Gano- Lethal yellowing (LY) is one of the Carolina to Florida. Although this disease derma infects clumping palms is when ma- most serious diseases of palms in Florida, has only been documented on about 40 or ture canes of these palms are removed. The but it also occurs in the Brownsville, Texas 50 species, it is believed that all palm resulting dead stump is quickly invaded by area, and parts of Mexico, Central America species are probably susceptible. Ganoderma spores. Once established on and the Caribbean. This the stump, this disease invades and kills microbe is spread only M 2) Lethal yellowing of healthy living canes until the palm is killed. by phloem-feeding in- coconut palm. Any palm tissue infected with Gano- sects such as the derma should be hauled to a landfill or in- leafhopper, Myndus cinerated, but never chipped for mulch, as crudus. Approximately • 3) Ganoderma butt rot this has been shown to transmit the disease 30 species of palms are on sabal palm. susceptible to LY. Symptoms of LY in most coconut palms may begin with mid-canopy or older yellow leaves that drop down against the trunk, but in some species such as Christmas palm these collapsing older leaves may not show any yellowing. In Malayan Dwarf coconut palms, leaves appear wilted, with little or no yellowing evident. Ganoderma butt rot is primarily a dis- to healthy palms. Stumps remaining after Blackening of the flowers and premature ease of mature palms in the landscape. palm removal should be dug out. Also, any fruit drop are also characteristic symptoms Symptoms appear as wilting and death of new conks should be prompdy and regu- of LY in coconut palms. the oldest leaves, but it gradually pro- larly removed to prevent the production of Lethal yellowing is best prevented by gresses up through the canopy until the additional spores. planting palms resistant to the disease, but bud is killed. Unfortunately, there is no it can be prevented in susceptible species chemical control for this fungus and fumi- 4) Potassium Deficiency by trunk injection with oxytetracycline. If gation of Ganoderma-infected stumps or Potassium deficiency is probably the the disease is diagnosed at a very early root systems is not effective in eliminating most widespread and serious nutrient defi- stage, antibiotic injection results in recovery this fungus. ciency of palms throughout the world. for about half of the treated palms. Com- One of the earliest and most diagnostic Palms have rather high requirements for mon palms known to be resistant to LY in- symptoms for this disease is the presence potassium and since they often grow in clude paurotis palm [Acoelorrhaphe of the fungal fruiting structure (conk) on highly leached, sandy or nutrient-poor wrightii), pindo palm [Butia capitata), Euro- the lower portion of the trunk. These soils, this element is deficient to some de- pean fan palm (Chamaerops humilis), areca conks start out as small white lumps but gree in virtually all palms in the landscape. palm (Dypsis lutescens), thatch palms (Coc- quickly mature into brown woody brackets Deficiency symptoms vary among palm cothnnax and Thrinax spp.), royal palms up to 1 foot across, releasing millions of species, but usually begin with small translucent yellow to orange or necrotic results in potassium being removed from spotting on the oldest leaves, readily visible progressively younger leaves that were pre- Injecting Palms if the leaf is held up to the light. As symp- viously symptom-free. If this practice con- toms progress, these older leaves may take tinues, the palm will quickly run out of old Made Easy on a yellow-orange to bronze color that is leaves from which to remove potassium for For many years, arborists have faced visible from some distance. One of the key new growth and the palm then enters a numerous palm tree problems: nutri- symptoms on most species is the presence state of rapid decline. At this point, the tional deficiencies, borers and lethal of necrosis along the margins of the leaflets trunk diameter tapers to a point, all new palm yellows, to name a few. Recently, of older leaves. As this becomes more se- leaves emerge stunted, chlorotic and friz- many professionals have turned to vere, entire leaflet tips become withered or zled and death of the bud soon follows. chemotheraputant treatments. Many in frizzled in appearance, yet upon close ex- This late stage of deficiency is extremely the industry are using one of the many amination, the midrib of the leaf will re- similar in appearance to manganese defi- microinjection technologies that are main alive, though perhaps discolored. The ciency and only close examination of the available. gray frizzled old leaves typically found on symptoms of an individual leaf will reveal One problem in treatment exists, royal palms (Roystonea spp.) and the which problem is present. however, and this stems from the differ- golden-orange foliage of areca palms [Dyp~ In addition to poor soils, one of the pri- ence between the anatomy of palms and sis lutescens) are common examples of mary causes of potassium deficiency in all other trees. Palm trees are mono- potassium deficiency. palms is the use of fertilizers having high cotyledons. This fact makes them more Potassium is considered a "mobile" ele- nitrogen content in controlled release closely related to grasses than to other ment within plants. Under conditions of form, but low to moderate levels of potas- types of trees. deficiency, potassium will be removed sium in soluble form. This combination The configuration of the vascular tis- from older leaves and retranslocated up to forces rapid palm growth, yet provides in- sue is unlike that of any other type of sufficient potassium to tree. Instead of a ring of conductive tis- do so. Thus, the use of sue under the bark, the vascular tissues turf fertilizers in the of palms are made up of tight groups of vicinity of palm roots is conductive cells known as bundles. These a major cause of defi- bundles contain both xylem and phloem ciency in palms. tissue and are connected radially to Treat severe defi- other bundles by live and woody, non- ciency by broadcasting cambial structures. Because of this vascu- sulfur-coated potassium lar tissue orientation, palm trees translo- sulfate under the cate fairly evenly throughout their entire canopy at a rate of 1.5 cross-section at any given point up or lbs. per 100 sq. ft, every down the trunk. three months for a year When you need to microinject a palm, or more. To prevent a you must take into account: • height of the palm tree when calcu- A 4) Moderately severe potassium deficiency K-Mg imbalance from occurring under lating the dose of the chemotheraputant; on areca palm showing frizzling of leaflet tips. these circumstances, it is also necessary to apply a 100% coated palm maintenance • diameter of the microinjection holes fertilizer at the same rate and frequency to be as small as possible; newly expanding leaves where it will be in- starting six weeks after the first potassium • microinjection feeder tube to be corporated.

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