Recent rains have set the stage for root problems that are often referred to as “wet feet” (feet referring to roots) on trees and shrubs. Symptoms are often the same as those resulting from a lack of water or other root injuries and include withering of leaves, little terminal growth, small leaf size, yellowing of foliage, and dieback of shoots and roots. Some woody plant species are particularly sensitive to such conditions, including yews (injured by as little as 12 hours of saturated soil), rose, white birch, Norway and sugar maples, flowering dogwood, and forsythia, to name only a few. Water tolerance of many plants is discussed in Sinclair, Lyon, and Johnson’s book, Diseases of Trees and Shrubs. Most good tree ID books also list such sensitivities as part of the species description.
Woody plants (trees and shrubs) often show injury from water damage when a hot, dry spell occurs after heavy rains. The roots have been damaged. The water deficit caused by heat, sun, and wind pulls on roots to provide water to the foliage. Even if plants are watered, the injured roots cannot take up water fast enough to meet the demands of such environmental conditions.
Roots need oxygen to grow and to absorb nutrients. In a water saturated soil, the oxygen content is low; and, without oxygen, roots cannot respire properly and cannot absorb water. Even though there is an abundance of water, it cannot be utilized by the plant. For long-term management of such situations, you must improve drainage, lighten the soil with a mixture of organic matter and sand, and avoid too much addi-tional water. Keep in mind that improving drainage includes draining away from the planting site. A well prepared planting hole with plenty of organic matter will still hold water like a bucket if it is in clay soil.
If you are not certain that water is the problem, dig up some of the soil around the suspect plant. In a typical situation, if there is too much water, the soil is saturated and standing water may be evident. Roots are black or brown internally, instead of the white color of healthy, new roots. In most cases, fungicides do not help. Fungicides were developed to protect healthy plants from root-rot pathogens. They do not revive dead roots. The water problem must be alleviated for new roots to form.
Information on root rots of trees is available in RPDs no. 602, “Armillaria Root Rot of Trees and Shrubs,” and no. 664, “Phytophthora Root Rot and Dieback of Rhododendrons and Azaleas.” These RPDs are available in Extension offices or on the Web on the University of Illinois Vista Web site.