Littleleaf Disease
Littleleaf disease is the most serious disease of shortleaf pine in the Southeast. It is caused by a complex of factors including a non-native fungus, Phytophthora cinnamomi, low soil nitrogen, eroded soils, a plowpan (from farming), and poor internal soil drainage (Campbell and Copeland 1954). Often, native microscopic roundworms called nematodes and native species of the fungal genus Pythium are associated with the disease. Infected trees have reduced growth rates and commonly die within 12 years of symptom expression. Growth reduction and death generally occur only in older stands where competition for root space (and thus for water and nutrients) has become significant. Once trees are affected, there is little likelihood of recovery, but it is possible to delay tree death for a few years by thinning and applying fertilizer.
While shortleaf pine is the most seriously damaged host, loblolly pine is damaged to a lesser extent. Littleleaf disease has also been reported on Virginia, pitch, slash, and longleaf pines. Historically this root rot complex was also responsible for significant losses of American chestnut trees.
Affected pine stands are found on the Piedmont Plateau from Virginia to Mississippi. Additional scattered pockets of disease occur in eastern Tennessee and southeastern Kentucky. The disease has its greatest impact in Alabama, Georgia, and South Carolina (see figure below).
Management strategies based on the work of Campbell, Copeland, and others have been extensively implemented throughout the range of the disease. Primary strategies are silvicultural (Anderson and Mistretta 1982; Mistretta 1984). Overall, the most used management strategies are to regenerate littleleaf sites with the more resistant loblolly pine, or to allow the site to revert to a predominantly hardwood cover with the expectation that the hardwoods will break the plowpan.
Generally, the level of management significantly affects the occurrence and severity of this disease. Intensively managed stands are regenerated before losses become serious. Less managed stands are likely to suffer serious loss and appear as generally unhealthy stands.
Ownership affects management of this disease. Industrial stands managed for short rotation products are essentially unaffected by this disease while public land managed for older age timber or for old-growth aesthetics are vulnerable. Extensively managed, nonindustrial private land is susceptible to this disease, while intensively managed private land avoids the loss. Many managers of public land are implementing the strategy of converting to loblolly pine to avoid damage by this disease.
According to one estimate (Mistretta 1984), littleleaf disease was present in 35 percent of the commercial range of shortleaf pine, and was severe enough to be a factor in timber management on about 4 million acres. Losses attributed to littleleaf disease exceed $15 million per year. However, because of appropriate management there appears to have been a reduction in the amount and severity of littleleaf disease during the last several years.
As time passes, this disease will become less significant. However, it is difficult to project the ecological effects which will result from converting large acreages of shortleaf pine to loblolly pine.
Encyclopedia ID: p992
