Description: Prevent blackening by using fungicides, protecting from cold, and maintaining proper care. Causes: Blackening of Plumeria stems can be caused by fungal infections or cold damage. Solutions: Fungicide treatment: Apply appropriate fungicides as preventive measures to control fungal infections. Cold protection: Protect the cuttings from freezing temperatures by moving them indoors or providing proper insulation. Proper care: Maintain the overall health of the cuttings through proper watering, balanced fertilization, and stress management. Monitor and care: Regularly inspect the stems for any signs of blackening or rot and take appropriate action.