If you are seeing chewed frangipani leaves you probably have the tetrio sphinx or frangipani hornworm caterpillar feeding on them. This is a black caterpillar with yellow stripes that gets quite large and is usually seen here between July and September. Since leaves will be dropping soon why not let the caterpillar have them, as it helps to fertilize the ground with its frass. Thuricide or Dipel are Bt. products that control small caterpillars and are safe on other beneficial insects. For other caterpillar control measures see this link: http://edis.ifas.ufl.edu/ig012
Recently, we have seen a rash of frangipani or plumeria rust fungus (picture is a microscopic view of the rust spores). This disease produces a mass of tiny pockets of rust colored spores on the undersides of the leaves. Infected leaves become yellow-spotted on top and fall off the tree. This disease is most commonly seen during the mid to late part of summer. Although it may look rather menacing it normally does not cause any serious problem for the plant. Since the leaves are getting ready to drop off for the fall anyway, spraying with a fungicide is usually not warranted. It is best to pick up or rake away any infected fallen leaves and dispose of them in the trash. This will help to reduce the amount of spores available to re-infest the tree at a later date.