Hi Lisa, Thank you for your question. One of the most common issues that plumeria owners face is black spots on the leaves, which can be caused by a variety of factors, including fungal diseases, insect infestations, and environmental conditions. Control strategies include removing infected leaves, using fungicides (Neem Oil was a good choice.) or insecticides, and improving environmental conditions. Preventive measures include proper watering, fertilization, and pruning.

Fungal diseases, including frangipani rust, black tip fungus, and black rot. These can be caused by a variety of factors, including poor air circulation, high humidity, and over-watering. Symptoms of fungal diseases can include yellowing or browning of leaves, leaf drop, and black spots on the leaves.

Insect infestations, usually aphids, mealybugs, and spider mites (you would likely see fine webbing) are common and can cause these spots. They feed on the sap of the plant, which can lead to the formation of black sooty mold on the leaves. In addition to black spots, signs of insect infestations can include curled or distorted leaves andsticky residue on the leaves. Monitor the upper and lower sides of the leaves often to look for tiny insects. Rub your Plumeria leaves with cotton soaked in alcohol since this is an effective way to eliminate sap-sucking insects.

Environmental stressors like sunburn (scorching heat) and low humidity can also cause black spots on plumeria leaves. Plumeria plants require full sun to thrive, but exposure to too much direct sunlight can cause the leaves to become scorched and develop black spots. Low humidity can cause the leaves to dry out and turn black, while scorching heat can cause sunburn and black spots on the leaves. Overwatering can lead to root rot, which can cause the leaves to turn black. Water plumeria plants only when the soil is dry to the touch. Expecially avoid over-watering plants during winter because they are dormant during this period. Good soil drainage and air circulation are also essential to prevent root rot and fungal infections.

Black spots on plumeria leaves can appear as small specks or large patches. These spots can be black or dark brown in color. In some cases, the black spots may be surrounded by yellow spots or other discoloration. The leaves may also become distorted or discolored, and may eventually fall off the plant. Black spots can also affect the roots of the plumeria plant, leading to poor growth and development. This can be especially problematic if the roots become infected with a fungal disease.

If you opt to use a fungicide or insecticide,be sure to choose one that is safe for plumeria plants and follow the instructions carefully.

Be careful not to over-fertilize. Prune the plant regularly to promote air circulation and remove any diseased or damaged leaves. Stop fertilizing your plant if it is experiencing leaf spot diseases, of course, unless you need to correct a particular nutrient deficiency.

The links below will give you some general cultural requirements for plumeria:

https://plumeriacareguide.com/cultivation-and-planting/guide-growing-plumeria-indoors/

https://www.gardeningknowhow.com/ornamental/flowers/plumeria/growing-plumeria-plants-indoors.htm

Plumeria plants can be difficult to grow. Good luck!