Honeydew presence means aphid infestations in landscape plants. The following is more information.
You or your clients may notice honeydew on cars and sidewalks. This is a sign of aphid infestations in nearby trees or shrubs. There are a number of aphid species that feed in landscape trees and go largely unnoticed until honeydew rains down on surfaces where it is not wanted. Many tree species and large shrubs can be attacked by aphids. Fortunately, aphids are often “cleaned up” by ladybugs and other natural enemies and do not cause permanent harm to the trees. However, on nursery stock, landscape specimen plants, or trees that shade a client’s fancy car, control may be needed. Luckily there are a number of products such as imidacloprid, Tristar, Safari and others that can provide long term aphid suppression and can often be applied in foliar or drench applications.
Adapted from an article in the North Carolina Pest News http://ipm.ncsu.edu/current_ipm/09PestNews/09News7/pestnews.pdf