I have two Guava plants whose leaves start turning brown at its tips and gradually fall off. I have sprayed it with Malathion, feed 6 6 6 fertilizer and have seen no improvement. However, there is new growth on the plant.
Certified GKH Gardening Expert
Make sure that you are not over watering.
These plants are quite tolerant of a drier soil mix.
Fertilizing can be done every 3 months.
Here is a link to refresh you on the care requirements.