Some of the leaves on my large Dutchman’s Pipe have become shrivelled up and look like the front end of a conch shell
Can you please tell me what causes that and how to remedy it.
Dutchman’s Pipe (Arestolochia macrophylla) is seldom affected by disease (1). Your note seems to describe that the heart shaped leaves have been desiccated, deformed, and curled around themselves. It is most likely that you have insects like aphids that are sucking out moisture and nutrition from the infected leaves (2). First, carefully separate an infected leaf and look for any worm or bug that could be building a web or producing sap that causes the leaf to adhere to itself. Look on the back and front sides of the leaf. Do you see tiny insects? Aphids, mealy bugs and spider mites can cause leaves to curl and dry out as leaf sap is sucked by these small insects.
Some fungi infections cause leaves to thicken and become puckered. Look on the top of the leaf for dark spots and on the bottom of the leaf for signs of mildew or mold-dusty sticky white or black powder or filaments.
If insects or worms are present, I suggest you do the following: Hand pick off larvae or larger bugs on the leaves that are curled and carefully examine other leaves close to the infected leaves. Treat the area with a commercial insect spray (oil or soap based) from reputable nursery. If you find small insects like aphids or whiteflies, blast the affected areas with a powerful stream of water.
White or black powder is evidence that fungus is present. Treat the plant with a commercial fungal spray. Follow directions carefully. Prune the plant to improve air flow. Dispose of leaves in garbage and wipe your cutters with disinfectant. In the future don’t water the leaves only the soil around the roots. And don’t over water.
Keep a constant eye out for further infestations.
If you don’t notice any of the above signs of insects or molds, it is possible your plant has a viral infection spread by insects. If this is the case there is little one can do other than add compost and manure, and water the plant hoping that its own immune system will be able to fight off the pathogen.