Landscape and Nursery - Root Rots of Evergreens

Death or decline of evergreen trees and shrubs may be due to root rots. The is especially the case in poorly drained soils, soils with compacted layers, and soils with high winter water tables. The following is an article on root rots of evergreens from the University of Maryland Home and Garden Information Center.

Root rots can be caused various fungi, such as Phytophthora, Armellaria, Ganoderma, Fomes, Inonotus and Laetiporus spp. Symptoms include poor growth, loss of healthy needle color (needles eventually turn light yellow or brown), dark brown discolored wood at the base of the stem for several inches above the soil line, and loosening and separation of the dead lower bark. Infected shrubs often have extensive dieback. Other symptoms include slowed growth, smaller than normal needles, excessive cone or seed set, premature autumn color and winter twig dieback.

White fans of fungal growth, and dark brown shoestring like threads called rhizomorphs, may be found under the bark at the base of infected shrubs, or on the roots. The fruiting bodies that form from these fungi can be fleshy mushrooms that appear annually or hard shelf-like structures that are grow a new layer each year as the rot progresses. As a result of the fungal infection, the root system is reduced and dark brown.

Two specific root rot diseases on pine are procerum root rot and annosum root rot. Procerum root rot appears to be associated with trees ans shrubs planted in heavy, wet, poorly drained soils. Initial symptoms start in wet springs with delayed bud break and reduced candle elongation. By early to mid summer needles become wilted, and begin to fade to a lighter green color, before eventually browning. Dying needles usually remain on the tree. The bark and wood become spongy and develop resin pockets that ooze sap when punctured. Resin may also ooze through the bark at the base of the tree and exposed roots become resin soaked. Trees planted in wet soils with basal resin flow appear to diagnostic of this disease.

Annosum root rot infected trees and shrubs have a lighter than normal needle color with shorter than average growth. Roots become resin soaked but later become decayed with masses of string white decayed tissue. This root decay contributes to wind thrown tree damage and leaning trees after heavy storms. Reddish brown conks with white margins may appear at the base of the tree on the bark. This disease tends to be more prevalent on sandy soils that have a low seasonal water table.

Management strategies: Many fungi can be found on dead and dying shrubs. There are no cures once the shrub is infected and the fungi cannot be eliminated from the surrounding soil once the tree is removed. Although there are no chemical cures for these diseases they can be prevented by proper planting and maintenance practices. Avoid damage from improper pruning, lawn mowers and excavation within the root zone. Avoid planting shrubs in poorly drained compacted soils or in low areas where water collects. Also avoid placing plants near down spouts. Yews and pines especially will not tolerate wet soils. Construction of raised beds or grade changes may be needed to ensure proper drainage. Root diseases on older established plants can result from changes in water drainage patterns.

The University of Maryland Home and Garden Information Center has a great diagnostic web center at http://plantdiagnostics.umd.edu/index.cfm.

This article was reprinted form the University of Maryland Home and Garden Information Center diagnostic page.