Forest Pests: Insects, Diseases & Other Damage Agents

Leptographium Root Disease of Loblolly Pine Forest Health Guide for Georgia Foresters Written by Terry Price, Georgia Forestry Commission Adapted for the web by the Bugwood Network

(Loblolly Pine Decline)

An evaluation was initiated in Stewart and Chattahoochee Counties, Georgia in the spring of 1992 to assess the relationship between Leptographium procerum and southern pine beetle infestations. The fungus causes the disease known as white pine root decline but its association with loblolly pine and southern pine beetle attack had not been established prior to this evaluation.

Many of the southern pine beetle infested stands in the two counties had trees with thin often tufted crowns that were slightly off-colored (Figure 118). The symptoms closely resembled those associated with littleleaf disease caused by Phytophthora cinnamomi. A major timber company in the area requested an evaluation be done by the Georgia Forestry Commission to determine why southern pine beetle populations had remained high for 13 consecutive years.

Figure 118 photo by Terry Price

The roots of 180 southern pine beetle killed trees and 180 uninfested trees were sampled for signs of disease symptoms (pitch soaking) and insect feeding wounds from insects such as reproduction weevils. Various insect species are known to vector Leptographium spp.

The results indicated a correlation between southern pine beetle infested trees and Leptographium procerum and were published by the Georgia Forestry Commission in 1997.

Research conducted by Dr. Lori Eckhardt in central Alabama and published in 2003, describes the relationship between species of Leptographium and loblolly pine as that of loblolly pine decline (LPD). She proposed “LPD resulted from the debilitation of root systems of stressed trees by Leptographiun spp., which are vectored by various insects.” These trees are very susceptible to southern pine beetles. An earlier study (Otrosina et al., 1997) had also indicated that there was a “statistical correlation between the presence of species of the fungal genus Leptographium and the presence of southern pine beetle.”

The research by Eckhardt makes it possible to understand the process leading to a major decline problem with loblolly pine and its relationship to southern pine beetle severity. She found that “prescribed fire over time leads to multiple attacks by root feeding insects that repeatedly vector Leptographium spp. into the host root system. High Leptographium incidence was also statistically related to decreased resin flow, poor root condition, radial growth reduction, foliar transparency and crown density.” Further findings indicated that littleleaf disease was not associated with LPD. However, “a positive correlation between the presence of littleleaf disease in soils near loblolly pine and the distance of a hardwood infected with littleleaf was found.”

Most importantly, Eckhardt’s findings indicated, “loblolly decline was significantly correlated to site and stand physical factors. Slope and aspect were determined to be the predominant predictive variables when considering loblolly decline in central Alabama. There was a significant effect of tree age upon development of decline, but trees of all ages (29-62) studied, showed all levels of decline, with severity increasing with tree age. There were significant decline differences among the physioregions also, but decline was found in all of them. These data indicate that geographic and topological factors may be very useful to resource managers for predicting where loblolly decline will occur.”

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