Ornamental & Tree Diseases
Pitch Canker on Southern Yellow Pines
Pitch canker, caused by the deuteromycetous fungus Fusarium moniliforme var subglutinans, is a major disease of pines in the South. Before 1974, it occurred sporadically and damage was relatively minor. By 1976, the pitch canker fungus had established itself in over 1.1 million acres of Florida's pine forests; including 50% of the planted slash pine in east-central Florida. Shortly thereafter, pitch canker incidence increased significantly in west Florida and was found in southeast Georgia, South Carolina, and Mississippi. The disease is currently found throughout the South; primarily in seed orchards of slash, longleaf, Virginia, shortleaf, and loblolly pine. Other pine hosts include south Florida slash, pitch, table mountain, sand, and eastern white pine.
Losses occur in several forms including crown dieback, stem deformity, reduced growth rate, mortality as high as 25% in pole sized stands, and reduction in seed quantity and quality.
The pitch canker fungus overwinters as mycelium and sporodochia in infected stems of standing trees and logging debris. Conidia, produced in sporodochia are wind disseminated primarily in the summer during wet periods. Occasionally deodar weevils, Pissoides nemorensis, which breed in dying trees and feed on phloem of healthy trees, transmit the pitch canker fungus. The pitch canker fungus penetrates healthy pine tissues through wounds created by a number of agents including insects (deodar weevils, subtropical pine tip moths);fusiform rust galls; equipment (tree shakers, mowers, sprayers); harvesting cones; wind; and hail. The pitch canker fungus grows readily in susceptible tissues causing the host to produce a number of characteristic symptoms.
Initial yellowing of needles is quickly followed by bright reddish-brown discoloration. Dead needles may persist for more than a year, fading to a dull grayish-brown. New growth developing from previous years infection rapidly wilts, turns brown, and dies. Dieback of shoots of the current years growth is one of the first symptoms produced by infected trees. Terminals and upper laterals are most often affected. Infected tissues are frequently resin soaked and localized cankers are produced (annual on small diameter branches and perennial on larger branches). Wood beneath cankers becomes discolored and resin soaked.
Characteristic signs include the presence of cushion-shaped, salmon to pink colored sporodochia in needle depressions on pine shoots and branches and bark surfaces. Microconidia and sickle-shaped macroconidia can be observed with the aid of a microscope.
Management recommendations include:
1. Exclusion of the pathogen by preventing infected material from entering orchards.
2. Eradication or reduction of the pathogen by removing infected trees.
3. Use genetically resistant selections.
4. Avoid wounding trees, including anchor roots, especially from July through November. Properly adjust and operate tree shakers. Instruct equipment operators about the significance of not wounding trees during mowing and spraying operations. Harvest cones by clipping rather than tearing.
5. Protection of host with insecticides to reduce populations of deodar weevil and other potential insect vectors of the pitch canker fungus.
6. Maintenance of stand vigor.
7. Avoid over-fertilization, especially nitrogen. An increase in disease incidence has been associated with excessive nitrogen.
8. Establish orchards on well-drained sites.