The bare trunks and lush crowns of the various palm species that dot tropical and subtropical climates add architectural elements to any landscape. Palms are bold accents when silhouetted against buildings or lining roads and driveways. Whatever type of palm you grow, several problems related to management practices, diseases or pests may afflict the trees.
Palms need sufficient irrigation or they may exhibit signs of drought stress, including poor growth and yellowing leaves. Specific watering requirements vary by palm species. Typically, palms should be watered every two weeks during the warm summer months, with watering reduced to once a month in the fall and winter, according to the University of Arizona College of Agriculture. When watering, most species react well to receiving enough water that the soil is moist to a depth of 24 inches.
Poor Soil Nutrients
Palms need adequate soil nutrients to maintain fast growth and lush foliage. The university recommends spreading a fertilizer labeled for use on palm trees. If no palm-specific product is available, apply a fertilizer that has a ratio of 30-10-30 (nitrogen-phosphorus-potassium) or similar. The university suggests fertilizing every spring and summer as a preventative measure against soil nutrient deficiencies.
The Phaeochoropsis neowashingtoniae fungus causes the common diamond-scale disease that afflicts palm foliage, according to the University of California Integrated Pest Management Program. The disease starts as tiny black dots on the palm's leaf blades followed by widespread foliage loss. It's most common during moist weather seasons. Risks can be minimized by growing palms that are naturally resistant to the disease--the university recommends Mexican blue palm (Brahea armata) and the Chinese fountain palm (Livistona chinensis)--and allowing the soil to dry thoroughly between watering. The problem will typically resolve itself if the palm's health is sustained. Otherwise, apply a fungicide like fixed copper spray to kill the fungus.
A palm that has rotting leaf tips, stunted new leaf growth or trunk rot may have the pink rot disease, caused by the Nalanthamala vermoeseni fungus. Palms most susceptible to the disease include those that aren't fertilized, receive too much water or are under stress from cold weather. The best treatment strategy, according to the UCIPM, is to minimize plant stress by giving the palm the species-specific care that it needs. Leaves that are loose can be removed and discarded to avoid spreading the fungus spores. Treat severe infestations with a fungicide formulated with mancozeb.
Red Date Scale
Red date scale insects (Phoenicococcus marlatti) attack palms throughout the Americas, Asia, Europe and Africa, according to the University of Florida Institute of Food and Agricultural Sciences. The insects attack the base of the palm fronds where they leave black deposits and cause foliage death. Common palm hosts include rattan palms, various date palms and some fan palms. The university suggests spraying the palm with a strong jet of water. Repeated spraying sessions keep the insect in check. Insecticides formulated with horticultural oils like neem oil also eradicate this pest.