A uniform yellowing or browning of the edges of leaves on broadleaf plants or the tips of evergreen needles is a symptom of a condition called scorch. This problem occurs most commonly on linden, maple, ash and cottonwood. The problem usually is more severe on the south or southwest side of the tree or on the side nearest a source of radiated heat, such as a brick wall or street. Severe scorch can result in premature leaf or needle loss.
Prolonged dry periods accompanied by warm, dry winds, create an imbalance in trees in which moisture is lost through transpiration faster than the roots can supply it to the leaves. This results in the drying out and death of leaves and sometimes branch tips.
Leaf Scorch of Ornamental Trees & Shrubs, University of Missouri Extension
Leaf Scorch of Trees & Shrubs, Purdue Extension
Image from Michigan State University Extension.