Question
QUESTION: Do seagrape trees shed all their leaves at any time of the year?

ANSWER: They will if the temps drop low enough, usually below freezing, otherwise they will shed but leave some attached.

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QUESTION: Are there any signs to look for on the tree itself or leaves on the ground as to the cause of the leaves shedding as being from cold or disease? And does this include all species in Florida?

Answer
Its very difficult to differentiate between cold stress and fungal problems during the Winter, for the symptoms are similar; wait until Spring and new growth emergence, and if there is a problem, it will manifest itself during the Summer. Diagnosing problems with most plants can be difficult, even for professionals, but if there is discoloration of leaves and/or leaf shed, then a sample needs to be taken into your local Cooperative Extension Service, and they will send it on for analysis.