Annosum root rot Heterobasidion annosum, can be a serious problem of pines in plantations that have been thinned one or more times. Loblolly, slash and white pines are affected most but shortleaf and longleaf are sometimes infected. The fungus that causes annosum root rot reportedly enters pine stands when its airborne spores land on freshly cut stump surfaces. The spores progress downward into the roots and then spread to adjacent healthy trees through root contacts in the soil. Field evaluations conducted by the Georgia Forestry Commission tend to support the notion that stands are infected well before they are thinned and that individual tree infections may occur as early as age five. Thinning would then create dead stumps in which the fungus would proliferate from and then spread into nearby standing trees. Roots wounded during the plowing of firebreaks or road building as well as insect feeding may create wounds for infection. Infected trees begin to show symptoms 3-5 years following thinning. Crowns will thin, turn light green to yellow and have shortened needles that may be tufted at the branch ends. These symptoms are very noticeable when sick trees are compared to healthy trees. Crown symptoms are more pronounced in loblolly than in slash pine. The fungus can rot the roots so bad that some trees may fall over on their own or do so during moderate to heavy winds. Wind-thrown trees in a pine plantation may indicate root rot. The roots of wind-thrown trees can be examined for resin soaking (an early infection symptom), or for white stringy decay (an advanced infection symptom) (Figure 115). These symptoms along with wind-throw are usually positive signs that root rot is present. Ips infestations appearing 3-5 years after a thinning often indicate the presence of annosum.
Occasionally the fungus will develop fruiting bodies of conks at the base of living and dead trees or stumps (Figure 116). These conks are hard to see because they are frequently formed below the litter layer around the tree or stump base and are most prevalent during the cool wet winter months. Annosum root rot is found throughout Georgia on most forested sites, however, the most hazardous sites for the disease are characterized by deep sandy sites along the fall line of the state. It is best to consult with a soil scientist or forester for a more detailed description of a particular site. Following is a broad classification of sites for possible root rot occurrence: High Hazard - Sandy or sandy loam soils with at least 65% sand in the upper 12 or more inches above a clay layer and with no high seasonal water table. Intermediate Hazard - Silt and silt loam soils 12 or more inches deep. Low Hazard - Poorly drained clay and clay loam soils or those with high water tables. Managing Established Stands If plantations are severely infected with annosum (>50%), they should be clearcut and regenerated. Usually by this time infection centers are scattered throughout the stand and future thinnings will necessitate removing too many trees thus leaving the stand understocked. When regenerating high hazard sites a wider spacing should be used. This will delay the first thinning and ultimately reduce the total number of thinnings made during the rotation. Low hazard sites require no special planting treatments.
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Forest Pests: Insects, Diseases & Other Damage Agents |
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