Answer: There are several possible causes for the dieback. Pineapple guava is marginally hardy for your location and can suffer some cold damage to trunk and major branch tissues in some winters. This often shows up in the warm season when the trunk or branches can no longer supply the increasing demands of the leaves.
Other possibilities include root losses from disease or periods of soggy soil, or canker diseases on the branches. Check the plant trunk and branches carefully for splits or cankers and evaluate the plant location for possible soil drainage problems. Prune to remove dying branches below the damaged areas, dipping pruners in rubbing alcohol between cuts.
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