To prevent aphids from infesting your Plumeria, practice good garden hygiene by removing weeds and debris, which can attract pests. Attract natural predators like ladybugs or lacewings by planting flowers that they feed on. Inspect your Plumeria regularly and hose off aphids with a strong stream of water. Applying neem oil or insecticidal soap can also deter aphids without harming beneficial insects. Avoid using excessive nitrogen fertilizers, as lush foliage may attract aphids. A balanced ecosystem and proactive pest control measures can help keep aphids at bay.