There are a few things that can affect these trees. Fungus, canker, blight and aphids are common. If you call the nursery they can recommend a few landscapers that might be able to take a look.
Im No Landscaper but I suggest calling one to address your question ... Or google how to care for your trees I did so for my butterfly palms and I was able to save them by replanting them in drainable planters ... Good Luck with your trees
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