Root rots can be caused various fungi, such as Phytophthora, Armillaria, 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.
Other symptoms include slowed growth, smaller than normal needles on evergreens, excessive cone or seed set, premature autumn color, and winter twig dieback.
Infected plant material often has extensive 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 plants, 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 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.
Root rots of pine
Two specific root rot diseases on pine are procerum root rot and annosum root rot. Procerum root rot appears to be associated with trees and 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 in sandy soils that have a low seasonal water table.
Prevention and management
Many fungi can be found on dead and dying trees and shrubs. There are no cures once the tree or shrub is infected and the fungi cannot be eliminated from the surrounding soil once the tree or shrub is removed.
Although there are no chemical cures for these diseases root rots can be prevented by proper planting and maintenance practices.
Avoid damage from improper pruning, lawn mowers, and excavation within the root zone.
Avoid planting trees and shrubs in poorly drained compacted soils or in low areas where water collects. Also, avoid placing plants near downspouts. 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.