If you have a maple tree in your yard, chances are you're familiar with leaf scorch. Even with the increased moisture this summer, leaf scorch is still an issue in Broomfield gardens. And it's not just maples that are affected. Other susceptible trees include aspen, linden, eastern redbud and evergreens.
Leaf scorch symptoms can include browning of the leaf margin, blackening of leaves or spots of dead leaf tissue between main veins. It frequently appears during hot, dry periods when plants cannot take up enough water to replace what is lost during transpiration, and is often mistaken for a disease problem.
There are a variety of underlying issues that can contribute to the development of leaf scorch. Primary among them is damage to plant roots. A healthy root system is able to conduct enough water — and nutrients — to the crown of the tree to support all of the foliage.
Several things can cause root damage in the landscape, including: obstacles that restrict root growth, as seen in street trees when space is physically limited; construction damage to roots, both from tillage and compaction; prolonged drought conditions because of lack of water in the fall and winter months as well as during warmer summer months; and chemical damage from herbicides.
Perhaps the most common cause of root damage seen in landscapes is overwatering. This might seem counterintuitive, but roots need water and oxygen in equal measures to function properly. Waterlogged soils severely damage feeder roots, so the tree cannot transport water effectively. Leaf tissue at the margin and center of the leaf furthest away from main veins is affected first. If the problem persists, the entire leaf can turn brown or black.
Trees prone to developing iron chlorosis in our alkaline soils, such as maples, are doubly affected. Chlorophyll protects leaves from the sun's scorching rays. When leaves are unable to manufacture chlorophyll, tissue is much more easily damaged.
Reflected heat also can scorch foliage. Plants located near the south and west sides of structures and those surrounded with rock mulch can develop signs of scorch.
There is no cure for leaves that have already been damaged, but with deep and infrequent watering, the tree can recover. Resist the urge to overwater. As mentioned above, this could be the primary cause of the problem. Make sure trees and shrubs are receiving water through the fall and winter months. During long, dry spells trees should be watered once per month as long as temperatures are above 40 degrees.
For more information about this or any other gardening topic, contact the Broomfield County master gardeners at 303-464-5554 or via email at email@example.com.
Colorado State University Extension in the City and County of Broomfield provides unbiased, research-based information about 4-H youth development, family and consumer issues, gardening, horticulture and natural resources. As part of a nationwide system, Extension brings the research and resources of the university to the community. The Broomfield County Extension office is at 1 DesCombes Drive, Broomfield, 80020. For information, call 720-887-2286.