Palm and Cycad Disorders in Trees
Insects that invade Trees
Asian Cycad Scale – Asian cycad scale (Aulacaspis yasumatsui) is a deadly scale insect that has caused widespread decline to the sago palm (Cycas revoluta) and severe damage to other cycads like the native coontie (Zamia floridana). The adult insects hide among the roots and stems and hatch into a crawler stage. The crawlers emerge and feed by inserting their piercing sucking mouth parts into plant tissue. They cover themselves with a waxy coating and remain on the stem feeding. They will appear as a multitude of small white specks encrusted along the blades of the fronds. In time they kill the plant tissues and ultimately the entire plant. The scale insects can be controlled using horticultural oil along with a contact insecticide. Contact a Horticultural Agent from the Cooperative Extension Service for specific information on treatments.
Palm leaf skeletonizer (Homaledra sabalella) – The palm leaf skeletonizer is the larva caterpillars of a moth that causes damage by feeding on both the top side and lower side of the palm leaves. It may also feed on stem tissue and can disrupt the vascular system and cause leaf death. The adult moth lays eggs on the underside of the leaf husk and the emerging larva feed on leaf tissue. Symptoms include splotches of brown dead tissue and large frass (excrement) build up along leaves. Although no control method has proven completely effective there are insecticides that have moderate success in controlling this pest. Consult with a horticultural agent with the Cooperative Extension Service for advice.
Palmetto Weevil (Rynchophorus cruentatus) – The palmetto weevil is a large beetle that produces larvae that attack stressed palms, particularly palms stressed during transplanting operations. The adult female beetle lays eggs at the leaf bases and the emerging larvae tunnel into the bud destroying vascular tissue and killing the palm. Canary Island and sabal palms are favorite targets but other species such as Washington palms are also susceptible. The crown will turn brown and collapse. The best control is to keep palms that are being transplanted healthy during the process. Insecticides such as Lindane and Dursban are often applied to palms being transplanted as a preventative.
Scales/mealybugs – Both soft-scaled and armored scale insects cause problems to palm as do mealy bugs. Soft-scale and mealybugs produce honeydew and the associated sooty mold.
Tree Disease problems
Fusarium Wilt – The fungus (Fusarium oxysporum) attacks the vascular tissue of the Canary Island date palm (Phoenix canariensis,) Senegal date palm (Phoenix Reclinata), and date palm (Phoenix dactylifera). Symptoms of the disease are abnormal patterns of leaf death. A stem may have dying leaflets on one side while the other side is still green. Eventually the entire stem dies. The disease is lethal and is spread by infested soil or by pruning tools that have the fungus on the saw blade. Pruning saws can be sterilized by soaking the tools for ten minutes in a solution of 70% isopropyl alcohol and 25% chlorine bleach or one part pine-sol to three parts water.
Ganoderma butt rot – The fungus (Ganoderma zonatum) infects over thirty five species of palms in Florida. The disease is not a root rot but decays the lower 4-5′ of the trunk. There is no known prevention for this lethal disease and once in a palm it is untreatable. The first symptom is the presence of the fungal fruiting body or conch emerging from the base of the palm. The conch is a creamy white when it first appears and later turns into a larger (2-3″ across) brownish shelf like conch. Shortly after the conch appears the older fronds will die and soon after the newer fronds will wilt and die. The fungus is spread by spores released from the conk. Remove conks when they appear to minimize the chance of infesting adjacent palms and remove the affected palm as soon as possible. The fungus typically remains in the soil for two years or longer. Do not replant a palm into the same area unless the contaminated soil is completely removed and replaced with new soil.
Phytophthora bud rot – Phytophthora bud rot is a serious disease of palms growing in warm moist climates. It is primarily caused by the fungus(Phytophthora palmivora). This soil borne fungus causes a discoloration of the younger leaves and ultimately a collapse of the bud. The bud can be easily pulled out by hand and the area where the bud was located will give off a foul odor. The disease is spread in water droplets that are splashed from plant to plant or by infected pruning tools. Once the bud is infected the palm will die. Fungicides such as Subdue Maxx or Aliette can be used as a preventative or will control the disease if detected early. Consult with a County Extension Horticulture Agent if you suspect that your palm is infected.
Thielaviopsis bud rot – Thielaviopsis bud rot is caused by the fungus(Thielaviopsis paradoxa) and can attack the bud, leaf or trunk. The infection can occur in the cut green petioles, in cracks on the trunk or on the leaf. Infections on the foliage can spread to the bud and kill the palm. Infections on the trunk can cause bleeding and rot. The rotted area will be susceptible to failure. Symptons of the disease on the foliage are the browning of the older leaves followed by browning of the new leaves. Symptoms of the disease on a palm trunk is the exuding (bleeding) of a dark liquid and soft decayed trunk tissue. Consult with a Horticultural Agent from the Co-operative Extension Service if you suspect your palm has this disease.
Miscellaneous problems with Trees
Trunk splits/cracks – Small vertical cracks on the trunk of a palm are commonly caused by too much or too little water or planting the palm too deep. Large vertical cracks are usually caused by too much water or damage during the planting or transporting of palms.
Trunk constrictions – A trunk constriction appears as a narrow area on the trunk and is caused by a disruption of the palm’s diameter for that year. Some of the causes are nutritional deficiencies, drought, hard freezes and over pruning.
Nutrient deficiencies – Many palm species are very susceptible to nutritional deficiencies. A high percentage of palms used in ornamental landscapes are exotic species that originate from tropical climates that have a different soil composition than our local soils. In the nursery environment palms are supplied with the nutrients to keep them healthy and make them appealing for sale. However, once placed into our native soils they may become deficient. Potassium is usually the most deficient nutrient, but other macro and micronutrients may be deficient as well. When purchasing a palm ask the grower about its nutritional needs and apply fertilizer as prescribed to keep the palm healthy. If a palm appears deficient call an agent at the Cooperative Extension Service and describe the symptoms. They may ask you to supply a soil sample for analysis. It is important to keep palms healthy as they are susceptible to disease and insect attacks once stressed.