Pitch Canker

Pitch canker is a disease of pines caused by Fusarium circinatum Nirenberg et O’Donnell [= F. subglutinans (Wollenweber & Rienking) P. E. Nelson, Toussoun & Marasas f. sp. pini Correll and others]. The disease derives its name from the induction of copious pitch flow associated with cankers of pines. The classic symptom is a bleeding, resinous canker of the main stem or trunk, terminals, large branches, shoots, and exposed roots. The canker is usually sunken and the bark is retained, while the wood beneath the canker is deeply resin-soaked. Dieback in the crown results from cankers forming on the branches or shoots. As the branches or shoots are girdled by the fungus, the needles turn yellow to reddish brown; later they turn grayish brown to dark gray. It may take several years, however, for a canker to girdle the main stem. The pitch-soaked wood is a diagnostic character useful in separating pitch cankers from most other maladies of pines (Dwinell and others 1985). The symptoms of pitch canker frequently vary by pine host and management practices. In southern pines, trunk cankers are common on Virginia (P. virginiana Mill.), longleaf (P. palustris Mill.), and eastern white (P. strobus L.) pines. Dieback is common on slash, loblolly, shortleaf (P. echinata Mill.), sand [P. clausa (Chapm. ex Engelm.) Vasey ex Sarg.], and pond (P. serotina Michx.) pines. Trunk cankers on slash pine are common in seed orchards and are usually associated with the use of tree shakers for cone removal. Cankers on exposed roots can be found on slash pine in seed orchards and other pines in landscape plantings (Dwinell and others 1985).

Pitch Canker

Pitch canker is an incomplete descriptive name for the range of damage caused by F. circinatum. The pathogen infects a variety of vegetative and reproductive pine tissues at different stages of maturity and produces a diversity of symptoms. Damage to pines by this fungus includes growth suppression, stem deformation, and tree mortality. The pitch canker fungus also causes mortality of female flowers and mature cones, and deteriorates seeds of several pine species. Dwinell and Fraedrich (1997) isolated F. circinatum from the surface and interior of immature shortleaf pine cones from a North Carolina seed orchard. They concluded that interior contamination by F. circinatum was not correlated with necrotic regions, caused primarily by insects, on the cone surface. The mode of entry of the pitch canker fungus into cones is unknown. Entire slash pine seedlots and entire longleaf pine seed-crops have been lost as a consequence of contamination by F. circinatum, which resulted in low seed viability and germination (Dwinell and others 1985). Current research is aimed at determining whether the pathogen is primarily on the seed surface or infects the embryo. Contamination of seed in longleaf and shortleaf pines is mostly on the seed surface (Dwinell and Fraedrich 1997, Fraedrich and Dwinell 1997). The fungus appears to be primarily external (Dwinell 1999). There is little empirical data linking seed contamination by F. circinatum with seedling cankers that occur in nursery beds and on outplanted sites. The major result of seed contamination by the pitch canker fungus is preemergence and postemergence damping-off (Dwinell 1999, Dwinell and Fraedrich 2000). In addition, pitch canker occurs in bare-root and container nurseries. Diseased pine seedlings show chlorotic or reddish brown needles and wilting. Pitch-soaked lesions usually occur at or near the soil line, but occasionally are found in the region of the cotyledonary node (Barnard and Blakeslee 1980). The pitch canker fungus has been associated with late-season mortality in longleaf pine nurseries (Carey and Kelley 1994).

Fraedrich and Dwinell (1997) concluded that F. circinatum is a wound pathogen of longleaf pine seedlings. Any fresh wound, regardless of cause or location, provides an infection court for the pathogen. Insects can create wounds that can be infected by airborne spores of the pathogen or serve as vectors. In the Southeastern United States, the deodar weevil (Pissodes nemorensis Germar) creates wounds that may become infected by airborne spores of the pathogen (Blakeslee and others 1978). Recent unpublished research suggests that the Nantucket pine tip moth [Rhyacionia frustrana (Comstock)] may not be associated with pitch canker in loblolly pine. In slash pine seed orchards, main stem cankers often develop after injury caused by mechanical cone harvesters. Also, injuries caused by wind and hail may serve as entry points. Hurricanes and tornadoes, in particular, have contributed to the intensification of the disease in some seed orchards (Dwinell and others 1985). The involvement of insects, interactions with other pine diseases, and numerous biotic and abiotic factors can influence the incidence and severity of infections by F. circinatum.

Annual mortality due to pitch canker in the Southeastern United States has been low. Southern pines, particularly loblolly, pond, and shortleaf pines, usually recover from outbreaks of shoot dieback (Barrows-Broaddus and Dwinell 1985, Kuhlman and others 1982). From 1945 to 1973, limited outbreaks of pitch canker were noted in the Southeastern United States, but the disease was not considered to be economically important. In 1974, a shoot dieback identified as pitch canker reached epidemic proportions on slash pine in Florida plantations and seed orchards, and on loblolly pine in North Carolina and Mississippi seed orchards (Dwinell and others 1985). These outbreaks spawned considerable research on pitch canker. Over the last three decades, pitch canker outbreaks in the South have occurred sporadically in time and place. Pitch canker has also evolved from a regional problem to one of national and international importance (Dwinell 1999). Because each outbreak has its own unique history, no specific management strategy has been developed to reduce or eliminate the threat of pitch canker disease. An integrated management approach, including chemical control, biocontrol, genetic selection for resistance, and altered cultural practices should be considered for specific hosts and growing conditions (Dwinell and others 1985). External contamination of pine seeds can be reduced or eliminated by appropriate seed treatments (Dwinell 1999, Dwinell and Fraedrich 2000). Because wounds serve as infection courts for F. circinatum, understanding the cause or causes of the wounding is tantamount to managing pitch canker (Dwinell and others 1985). In cases where the wounding agent is an insect, chemical control may reduce disease intensification. However, regulations on the use of chemical pesticides have severely limited this option. Biocontrol organisms have been ineffective (Barrows-Broaddus and Dwinell 1985). Variation in the incidence of pitch canker is common among clones within seed orchards, suggesting that genetic selection for resistance is possible (Barrows-Broaddus and Dwinell 1985, Dwinell and others 1985).