Healthy, undamaged palm trees can often resist attacks by disease organisms. Landscapers should provide palm fertiliser as directed by a local cooperative extension office or a local nursery, and keep high-nitrogen lawn fertilisers away from palms. Equipment used to trim palm trees should be sterilised before moving to the next palm tree. These steps may help palms stay healthy.
Fusarium oxysporum is the fungus most likely responsible for fusarium decline, which affects queen palms (Syagrus romanzoffiana) and Mexican fan palms (Washingtonia robusta). In queen palms, the leaves turn brown, beginning at the bottom and spreading to the top of the canopy. The leaves remain in position, however; they do not droop down. This odd behaviour makes it easy to tentatively diagnose fusarium decline. The symptoms are similar in the Mexican fan palm and a dark brown stripe will be visible on the stem of the leaf. The disease moves quickly so no fungicide treatment can be recommended. The affected tree should be removed immediately. The fungus is spread via pruning equipment so sterilisation of equipment between trees will help prevent infection.
Lethal Yellowing of Palms
A bacteria spread by the planthopper insect causes lethal yellowing of palms. This disease has been observed in a wide range of palms including coconut palms (Cocos nucifera), Chinese fan palm (Livistona chinensisa), windmill palm (Trachycarpus fortunei) and the Canary Island date palm (Phoenix canariensis), among others. The symptoms vary, but an early symptom of the disease may be the fruit dropping from the tree before it is ready. Then a yellow leaf appears at the top of the canopy as the older, lower leaves begin yellowing. Antibiotic oxytetracycline HCl injections into the tree trunk have proven effective in controlling the disease, when started early, when only one fourth of the leaves are yellow. Trees more heavily infected should be removed.
Pink rot is a secondary fungal disease that attacks weakened or stressed palm trees. It is caused by the fungus "nalanthamala vermoeseni." The University of California extension warns that this disease attacks most palms used in California landscaping. It affects the top of the palm where new leaves emerge. The symptoms include rotting at the tips and base of leaves and along the leaf stem. Palms that are planted too deeply, fertilised improperly, damaged during pruning, irrigated improperly or infected with other diseases are susceptible to pink rot. Prevention is the best management tool; however, the disease can be controlled with the fungicides thiophanate methyl and mancozeb.
Petiole blight of palms affects a wide variety of mature palm trees with trunks. It is less likely to occur in young palms. A fungus attacks the stem of the leaf and destroys the mechanisms that carry water to the leaf blades, thus killing the leaf. Older leaves at the bottom of the canopy will begin to die. A brown streak will be clearly visible along the leaf stem. While not usually lethal, the disease can compromise the tree. A broad spectrum fungicide may be helpful, according to the University of Florida extension.