Palm trees do not get borers or sunburned trunks. Borer damage doesn’t happen much probably because they are monocots.
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Many types of cacti have spines on the paddles to protect them from chewing-type predators like jackrabbits and desert cottontails. But insects can burrow in just under the skin.
Signs of plant disease are seeing the reason why the symptoms occurred in the first place. The reasons for leaf drop can be from many different signs.