ISA Certified Arborist Practice Exam 2025 – All-in-One Resource for Comprehensive Exam Success!

Aphids are small sap-sucking insects that commonly infest a variety of trees and plants. One of the most noticeable signs of an aphid infestation is the production of a sticky substance known as honeydew. This honeydew is excreted by aphids as they feed on the sap of the tree. It often collects on the leaves and surrounding surfaces, leading to the growth of sooty mold. Sooty mold is a fungal growth that develops on the honeydew, creating a black, powdery coating on leaves, branches, and other surfaces. This phenomenon can significantly reduce the aesthetic quality of the tree and block photosynthesis, which can eventually impact the tree's overall health.

The presence of honeydew and sooty mold is a clear indicator of aphid activity, making this answer the correct choice in identifying signs of an aphid infestation. The other options, while they may indicate different issues, do not specifically relate to aphids. Brown scabs on bark could be due to pest damage or environmental stress, visible webs on branches are typically associated with spider mites or web-spinning insects, and discoloration of roots may suggest root rot or other soil issues. Therefore, the defining characteristic of an aphid infestation is indeed the sticky honey