Treating fungal disease in palm trees is accomplished by understanding its underlying causes, then applying treatments that may include fertilizer, horticultural oil and fungicide. There are many different types of palm trees, including the California fan palm, date palm and king palm, all of which are susceptible to fungal diseases.
To treat palm tree fungus, first test the fungus itself and the surrounding soil to determine its cause. Apply fertilizer based on the results of the soil test, and add horticultural oil if the fungus is determined to be caused by insects or other pests. If the tree looks healthy apart from the fungus, remove the affected areas and apply fungicide. If the tree doesn't look salvageable, remove the entire tree and destroy its parts.