The angel trumpet plant is a relatively hardy plant and is not susceptible to many diseases, but might be affected by certain diseases and pests if the plant is not healthy to begin with. To help prevent diseases and pests, make sure the plant is properly cared for, and environmental issues, such as iron chlorosis, sunburn, heat stress, air pollution and oedema are not effecting the plant. If you do notice any of the listed problems with the angel trumpet, clear the disease and remove the offending environmental problem.
Leaf spot shows itself as various sized spots on the leaves of the plant. The color may also vary. The leaf spots are usually brown but may be black or tan. The spots may combine over time, giving the leaves a blotchy look. Keeping trimmed or fallen plant debris cleaned up helps prevent leaf spots. If the angel trumpet is prone to leaf spots, water from below rather than from above. Leaf spots may be removed by discarding the affected leaves.
Aphids are small, pear-shaped insects. They suck plant juices from the stem and leaves of the plant. An angel trumpet with aphids has pale or sometimes yellow spots on the leaves and stems. Eventually, the leaves turn brown, and might curl or become stunted. The aphids are usually found on the underside of the leaves. Spraying with water every other morning knocks the aphids off the plants. If using water does not remove the infestation, treat the plant with an insecticide, or introduce lacewings and ladybugs to the angel trumpet plants. Lacewings and ladybugs feed on aphids and are not harmful to the angel trumpet plant.
Whiteflies are generally found on the underside of the leaves of house plants and outdoor plants. They pierce the plant and suck its juices. Usually, whiteflies are just a nuisance, but they may become a threat if the infestation becomes too large. Whiteflies have white, powdery wings, and when disturbed, the adults fly off in a cloud of white.
Whitefly traps may be used to control whiteflies. Homemade whitefly traps can be made from using a sticky trap by coating cardboard with petroleum jelly or heavy grade motor oil. Hang the traps vertically near the plants. Discard and replace the traps as necessary. You can also try using insecticides, but some whiteflies have developed resistance to many of the over-the-counter insecticides available.