We have a usually vigorous Virginia Creeper over garage walls. Lately some of the leaves are turning white underneath and falling off. There does not appear to be any insects on the leaves. What is the cause and what can we do to stop this occurring? Thank you.
About the only pest commonly found on Virginia creeper are a couple varieties of leaf hoppers. These cover their eggs with a white substance, which may be what you are seeing, and their feeding can also damage and cause the leaves to fall off. Some information on leaf hoppers: https://www.gardeningknowhow.com/plant-problems/pests/insects/leafhopper-control.htm
For positive identification, take leaf samples to the Extension Service. This link will help you locate the nearest one: https://www.gardeningknowhow.com/extension-search/