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

Leaf scorch primarily results from an inadequate water supply, leading to the inability of trees and plants to maintain sufficient moisture in their leaves. When a plant experiences water deficiency, it cannot take up enough water through its roots to replace what is lost through transpiration. This can cause the leaf edges to turn brown, and eventually, the leaves may drop prematurely.

Inadequate water supply can arise from various conditions, such as drought, poor soil drainage, or competition for water from nearby plants. The stress from insufficient water supply can weaken the plant's overall health and increase its susceptibility to pests and diseases.

Conditions like excess rainfall, aphid infestation, or high humidity can impact plant health as well, but they are not the primary drivers of leaf scorch. Excess rainfall can lead to root rot and poor uptake of water, aphid infestations can cause leaf curling and stress, and high humidity generally provides a favorable environment for plant growth by reducing transpiration stress. However, none of these conditions directly cause the leaf scorching effect observed with drought stress caused by inadequate water supply.