Contents

• Introduction
  • Recognizing Pitch Canker
  • Cankers on Small Shoots
  • Cankers on Larger Shoots
  • Cankers on Older Growth

• Recognizing the Pathogen
  • In the Field
  • In the Laboratory

• How the Pathogen Enters the Tree

• Management Considerations
  • In Plantations
  • In Seed Orchards

• Additional Reading

INTRODUCTION
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Pitch canker (caused by the fungus Fusarium moniliforme var. subglutinans.) is a major disease of planted pines in the South. Crown dieback, stem deformity, reduced growth rate and mortality are most severe on slash pines, but Virginia, shortleaf, loblolly, longleaf, south Florida slash, pitch, Table Mountain, sand and eastern white pines are also susceptible. Before 1974 and the start of the present epidemic in northeastern Florida, the disease occurred sporadically and caused variable amounts of damage. By 1976, the disease was present on an estimated 1.1 million acres (445,000 ha). In several, severely affected, east-central Florida counties, more than 51 percent of the planted slash pines were infected. The disease has recently intensified in western Florida and is frequently found in southeastern Georgia and on planted slash pine in South Carolina.

Elsewhere in the South, damage has most often been restricted to seed orchards of slash, longleaf, Virginia, shortleaf and loblolly pine. Cone production has been dramatically reduced in severely diseased orchards. The disease is most severe in orchards where the trees have been wounded by natural means or by cultural practices. Some clones in seed orchards are severely affected while others in the same orchard remain disease-free.

In slash pine plantations, a large portion of the expected growth can be lost (figure 1). In pole-size stands in epidemic areas, mortality has been reported as high as 25 percent and infection levels have exceeded 90 percent (figure 2). Growth loss and stem deformity seem to be the primary losses in sapling-size trees (figure 3); infection in younger trees is relatively uncommon. Severely diseased pole- and sawtimber-sized trees often do not recover. Several thousand acres of slash pine plantations in Florida, and many valuable seed orchard trees southwide, have been prematurely cut because of this disease.

The destructive potential of pitch canker is sufficient to warrant increased attention to recognition of the disease and to consideration of management practices which may be useful in minimizing losses.

RECOGNIZING PITCH CANKER
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The fungus invades woody branch and main stem tissues and creates localized cankers. These cankers are annual on small-diameter shoots and perennial on larger shoots. Pitch flows freely (figure 4) from the diseased tissues, even on small-diameter shoots. The wood beneath the cankers becomes discolored and thoroughly resin-soaked (figure 5). These symptoms are characteristic of most pitch cankers and will help you distinguish this disease from other canker diseases and most insect injuries.

Cankers on Small Shoots

Cankers on small shoots result in crown dieback symptoms typical of the disease on slash pines in plantations. Cankers on small shoots also result in crown dieback of shortleaf and loblolly pines in seed orchards. Although the trees are infected mostly during the summer and fall, you are most likely to notice the symptoms in the late fall, during the winter or in the early spring. During that period the fully expanded needles turn bright reddish-brown (figure 6). Dead needles may persist on some diseased branches for more than a year, during which time the needles fade to a dull, grayish-brown color (figure 7).

Cankers on Larger Shoots

Cankers on larger branches or on the upper portion of the main stem often do not kill the shoot during the first season. If these cankers grow during the winter end spring they may girdle the larger shoots. New growth will then droop, turn brown, and die (figure 8).

Cankers on Older Growth

Cankers on the larger portions of the main stem and on large branches live longer and are usually accompanied by large amounts of resin flow, sometimes covering several feet of the stem (figure 9). Such cankers are relatively uncommon in infected slash pine plantations, but are more common on pines in seed orchards and urban plantings. The bark remains on the canker face, which may be slightly depressed. The wood beneath the canker is pitch soaked, often to the center of the stem. Large portions of the tree crown can be killed when such cankers eventually girdle the stem or branch. Do not confuse these symptoms with similar symptoms occurring at the base of sand pines affected by certain root and butt diseases.

RECOGNIZING THE PATHOGEN
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In the Field

The fungus produces spores in small, cushion-shaped, salmon-pink colored structures (sporodochia) (figure 10). You are most likely to see sporodochia in the small depression where needles were formerly attached to the diseased branch. While not always present on diseased shoots, these structures can be found at any time of the year if you carefully examine branches whose remaining needles are still somewhat reddish-brown.

In the Laboratory

Because fruiting structures can be absent, and are usually inconspicuous, positive identification requires laboratory culturing and isolation. There are many ways to isolate the pitch canker fungus from symptomatic tissues. One highly effective method is as follows:

• Collect disease samples from living branches that have both diseased and healthy tissue.
• With a sterilized knife, remove the outer bark, exposing the canker margin.
• Using aseptic techniques, remove 1/4 inch (6 mm) square wood chips from the canker margin, briefly dip the chips in 95 percent ethanol, and shake off the excess alcohol. Flame sterilize the outer surface of the chip, being careful not to overheat the sample.
• Transfer the surface-sterilized chips to potato dextrose agar or to a Fusarium-selective media as described by Nash and Snyder. Incubate plates for 5 to 10 days under normal laboratory lighting and temperature conditions.
• On the selective media, the pathogen appears as slow-growing, granular, white colonies (figure 11). Transfer a portion of the colonies to fresh potatodextrose agar media or 2 percent water agar (supplemented with a washed, autoclaved, carnation leaf) for positive identification. The pitch canker fungus produces characteristic microconidia, macroconidia, and polyphialides (chlamydospores are absent) (figure 12).

HOW THE PATHOGEN ENTERS THE TREE
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Wounds are readily infected by the pitch canker fungus. Insects such as the deodar weevil (Pissodes nemorensis, figure 13) and the subtropical pine tip moth (Phyacionia subtropica) create wounds which can be infected by airborne spores of the pathogen. In slash pine seed orchards, bole cankers often develop through injuries caused by mechanical shakers (figure 14) used in cone collection. Infections frequently occur at cone scars on loblolly pines when the cones are removed from the branches during harvesting (figure 15). Weather-related injuries such as those from wind and hail may also serve as entry points. The fungus is also known to infect fusiform rust galls.

MANAGEMENT CONSIDERATIONS
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Specific control recommendations cannot be formulated until further research results become available. Until such guidelines can be developed, the following items are presented as considerations that may be useful in the management of this disease in plantations and seed orchards. These management considerations are based on extensive field observations and the most current research information available.

In Plantations
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   Salvage. -- The decision to salvage severely diseased plantations depends on the incidence (number of infected trees) and severity (amount of infection in each tree) of the disease in the stand, the expected future course of the disease, and the response of the infected trees. If stem-deformity, reduced growth rates, and lengthened rotations can be tolerated in sapling-size slash pines, moderately infected stands will normally recover. However, deformed stems may be more prone to breakage during windstorms. In severely infected pole-size slash pine stands, growth reduction and mortality losses may warrant salvage harvesting prior to scheduled rotation age. In addition, harvesting the infected trees should reduce the abundance of the pathogen in the area, thereby reducing the exposure of nearby stands.

   Logging debris. -- When possible, burn or broadcast logging debris. This practice will reduce the amount of the pathogen in the infected branches and thereby may minimize the exposure of nearby stands.

   Thinning slash pines. -- When economically feasible as a forestry practice, consider thinning of slash pine plantations with low disease incidence when they are located in high hazard areas (merchantable stands in outbreak areas). Stocking reduction in plantations with little disease will reduce competitive stress. This may, in turn, increase the resistance of the trees to future attacks or allow better recovery from previous infections. The effectiveness of this type of thinning has not been demonstrated, but removal of diseased trees during the thinning may limit future losses by reducing the level of airborne spores of the pathogen and by minimizing growth loss in the plantation. Removal of severely infected and low vigor trees may also remove some breeding sites (figure 16) for the deodar weevil, an insect that can vector the pitch canker fungus and can produce wounds that can be readily infected. Such thinnings should be done between December and May except during prolonged droughts or when bark beetles are a problem in the area. Treat stumps for annosus control when thinning stands on high hazard sites for annosus root rot.

   Regeneration. -- Consider natural regeneration of native stands or use disease resistant seed sources when they become available. Because slash pines vary in their susceptibility to pitch canker, occurrence of the disease may vary according to seed source. In many cases where pitch canker is epidemic in planted stands, the incidence of the disease is very low in natural stands derived from local seed sources. When harvesting such natural stands, consider regeneration by the seed tree method to preserve and use the native seed sources which may be more resistant to the disease. As pitch canker resistant seed and seedlings become available, use these sources for the artificial regeneration of stands in areas where damage from pitch canker might be anticipated.

   New plantations. -- Do not establish new plantations near diseased stands. Exposure to the fungus or its vectors may be reduced by avoiding close contact with infected stands.

   Water management. -- During the last half of the rotation, when water demands are the greatest, consider modifying drainage systems to help retain more water on the site during droughty periods, thus reducing possible moisture stress in the trees.

   Stocking levels and fertilization. -- Pitch canker has been very damaging in some fertilized or overstocked slash pine stands. While further research is needed to clarify any possible relationships between these factors and the frequency or severity of pitch canker, increased spacing (decreased stocking) of new plantations may result in reduced levels of competition-induced stress as the plantations near rotation age—the period when maximum demands are placed on the site.

In Seed Orchards
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   Wounds. -- Avoid wounding trees, especially from July to November. Because wounds serve as means of entry for the fungus, this action should reduce disease occurrence.

   Tree shakers. -- Properly adjust and operate tree shakers. Tree shakers can wound the tree at the point of attachment and throughout the crown. Take special care to minimize the damage!

   Roguing. -- Consider roguing trees with bole cankers. Further growth of these cankers may kill the trees.

   Clip the cones. -- Harvest cones by clipping rather than tearing to help reduce wounding. See figure 15. Cone harvesting produces wounds during the critical infection period and can result in multiple infections throughout the crown.

   Mowers. -- Avoid mower damage to the tree stem and anchor roots.

ADDITIONAL READING
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Barrows-Broaddus, J.B. and L.D. Dwinell.
   1979. Variation in virulence of diverse sources
   of Fusarium moniliforme var. subglutinans on 
   Virginia and loblolly pine. Phytopathology 69:522. (Abstr.)

Bethune, J.E. and G.H. Hepting.
   1963. Pitch canker damage to south Florida
   slash pine. J. For. 61:517-522. 

Blakeslee, G.M. and D.L. Rockwood.
   1978. Variation in resistance of slash pine to 
   pitch canker caused by Fusarium moniliforme 
   var. subglutinans. Phytopath. News 12:207-208. (Abstr.) 

Blakeslee, G.M., S.H. Kratka, R.A. Schmidt and C.S. Moses.
   1978. Sporodochia of the pitch canker fungus 
   (Fusarium moniliforme var. subglutinans) as found on 
   diseased slash pine in Florida. Plant Dis. Rep. 62:656-657.

Blakeslee, G.M., S.W. Oak, W. Gregory and C.S. Moses.
   1978. Natural association of Fusarium moniliforme var. 
   subglutinans with Pissodes nemorensis. 
   Phytopath. News 12:208. (Abstr.) 

Blakeslee, G.M., R.D. Dorset and S.W. Oak.
   1979. Inoculum dispersal of the pine pitch canker 
   fungus, Fusarium moniliforme var. subglutinans. 
   Phytopathology 69:1022. (Abstr.) 

Dwinell, L.D. and W.R. Phelps.
   1977. Pitch canker of slash pine in 
   Florida. J. For. 75:488-489. 

Dwinell, L.D.
   1978. Susceptibility of southern pines to infection 
   by Fusarium moniliforme var. subglutinans. 
   Plant Dis. Rep. 62:108-111. 

Dwinell, L.D. and J.B. Barrows-Broaddus.
   1979. Susceptibility of half-sib families of slash 
   and loblolly pine to the pitch canker fungus, 
   Fusarium moniliforme var. subglutinans. Phytopathology
   69:527 (Abstr.)

Dwinell, L.D., P.L. Ryan and E.G. Kuhlman.
   1977. Pitch canker of loblolly pine in seed orchards. 
   In: Proc. 14th South. For. Tree. Improv. Conf., p. 130-137. 
   (Gainesville, Fla., June 1977).

Hepting, G.H. and E.R. Roth.
   1946. Pitch canker, a new disease of some 
   southern pines. J. For. 44:742-744.

Kraus, H. S. and W. Witcher.
   1977. Survey of pine pitch canker in 
   South Carolina, Plant Dis. Reptr. 61 :976-978.

Kuhlman, E.G., L.D. Dwinell, P.E. Nelson and C. Booth.
   1978. Characterization of the Fusarium causing pitch 
   canker of southern pines. Mycologia 70:1131-1143.

McGraw, J.R., R.C. Wilkinson, R.A. Schmidt and E.M. Underhill.
   1976. Tip moths and pitch canker in Florida. Inst. Food and 
   Agric. Sci., Univ. Of Fla. Prog. Rep. 76-1. 4 p.

Nash, S.M. and W.C. Snyder.
   1962. Quantitative estimations by plate counts of propagules
   of the bean rot Fusarium in field soils. Phytopathology 52:567-572.

Phelps, W.R. and C.W. Chellman. .
   1976. EvaIuation of "pitch canker" in Florida slash pine 
   plantations and seed orchards -- 1976. USDA For. 
   Serv., Southeast. Area, Atlanta, Gal, Unnumb. pub. 22pp.

Schmidt, R.A. and E.M. Underhill.
   1974. Incidence and impact of pitch canker in slash pine
   plantations in Florida. Plant. Dis. Rep. 58:451-454.

Schmidt, R.A.
   1976. Pitch canker in Florida: History, current status and
   future research. In: D.R. Crowe (ed.). Recent development in 
   forestry research: smoke management, nonpoint source
   pollution and pitch canker. Univ. Fla. Resource 
   Rep. 3, p. 54-57, Gainesville, Fla.

Schmidt, R.A., R.C. Wilkinson, C.S. Moses and F.S. Broerman.
   1976. Drought and weevils associated with severe incidence 
   of pitch canker in Volusia County, Florida. Inst. Food and 
   Agric. Sci., Univ. of Fla. Prog. Rep. 76-2. 4 p.

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