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How to Manage Pests

Pests in Gardens and Landscapes

Pitch Canker

Published 2/03

In this Guideline:

Identification
Vectors of pitch canker
Disease progress in native and urban forests

Pitch canker is a disease of pine trees that is caused by the fungus Fusarium circinatum. Douglas fir can also be infected, but this is rare and infected trees are not severely damaged. The disease was first observed in California in Santa Cruz County in 1986. Since then it has spread rapidly and now occurs in 18 coastal counties. Most pines native to California are susceptible to pitch canker, but Monterey pine (Pinus radiata) is the most widely affected host. Pitch canker has also been reported in Mexico, southeastern United States, Japan, Spain, Chile, and South Africa. Genetic analyses of F. circinatum populations from around the world indicate that the pathogen originated in Mexico, and its recent introduction into California came by way of the southeastern United States.

IDENTIFICATION

The fungus causes infections (lesions) that can encircle or girdle branches, exposed roots, and the main stems (trunks) of pine trees. The tips of girdled branches wilt as a result of obstructed water flow, causing the needles to turn yellow, and then red. The fascicles (needle clusters) eventually fall off, leaving bare branch ends. Multiple branch infections can cause extensive dieback in the crown of the tree and may lead to tree mortality. The tree produces copious amounts of resin (pitch) in response to an infection. Flattened or slightly sunken cankers (large infection sites) on the main stem of the tree usually appear after the tree already has multiple branch infections. The fungus is not known to move within the tree; therefore, each canker or lesion is a separate and distinct infection. The flow of resin from main stem infections can coat the bark up to several feet below the infection site. Honey-colored, resin-soaked wood is also a characteristic symptom of the disease and can be observed by peeling back the bark near a lesion. Infected trees are often attacked by engraver beetles, which cause the death of additional branches, tree tops, and the entire tree.

Certain insects and other pathogens, often in combination, can also cause branch tips to wilt or other damage resembling that of pitch canker (Table 1). Though the disease can usually be accurately diagnosed by symptoms, diseased tissue must be cultured in a laboratory for a definitive identification.

Table 1. Comparison of Pine Tree Maladies with Some Similar Symptoms.¹

Malady

Oozing or streaming pitch

Lumpy, protruding, or tubular masses

Yellow to red wilted tip needles

Yellow to red unwilted tip needles

Dead tips, needle drop

Cones or conelets abort

Swelling on branches

Silk webbing on tips

pitch canker

Diplodia canker and blight

blight, Aleppo pine

western gall rust

weevils

red turpentine beetle

Ips bark beetles

cone beetles

twig beetles

injuries, pruning wounds

salt, wind, or drought dieback

shade-suppressed branches

caterpillars

1	Other abiotic disorders such as poor growing conditions and inappropriate cultural practices also can cause many of these symptoms.
2	Extensive branch swelling and distortion caused by dwarf mistletoe may cause resin flow.

KEY
*	Symptom occasionally occurs
**	Symptom usually occurs
Adapted from: Adams, D. Unpublished. Pitch Canker: An Introduced Disease. Davis, CA: Calif. Dept. For. Fire Protection; Dallara, P. L., A. J. Storer, T. R. Gordon, and D. L. Wood. 1995. Tree Notes 20. Sacramento, CA: Calif. Dept. For. Fire Protection.

VECTORS OF PITCH CANKER

Insects are believed to transmit the pitch canker fungus during exploratory feeding on trees. The fungus has been isolated from a number of insects, and the following insects are capable of vectoring the pitch canker pathogen: engraver beetles (Ips spp.), twig beetles (Pityophthorus spp.), cone beetles (Conophthorus radiata), and deathwatch beetles (Ernobius punctulatus). Adult spittlebugs (Aphrophora canadensis) have not been demonstrated to carry the fungus, but their nymphs do create wounds that may become infected if fungal spores are already present on the branch surface.

DISEASE PROGRESS IN NATIVE AND URBAN FORESTS

Based on the distribution of pitch canker in California, it can be concluded that the mild climate of the central and southern coast is conducive to disease development. In a survey of 39 plots on the Monterey Peninsula, strong trends were found with respect to disease severity and geographic location. On average, trees in plots located adjacent to the coast had significantly higher levels of disease than trees in plots located just a few miles inland. Furthermore, disease increased more rapidly in coastal plots than in inland plots. The difference in disease development between inland and coastal locations was especially striking because the inland plots are all within a few miles of the coast.

Results from that same survey also document significant differences in disease severity in the urban forest versus the natural forest. On average, trees in landscaped areas and small open-spaces had higher levels of disease than trees in larger, less disturbed forests.

Pitch canker can result in extensive damage and even death of infected trees. However, not all infected trees become severely diseased, and of those that do, some recover. Experiments under controlled conditions show that susceptible trees repeatedly exposed to the pathogen may gain resistance over time. For example, trees deliberately inoculated four times with F. circinatum over a 2-year period developed progressively smaller lesions each time they were inoculated. Likewise, there have been numerous observations of severely infected trees recovering from infection after a period of 6 to 7 years. Therefore, landowners and land managers should take a conservative approach to removing diseased trees because there is a possibility they may go into remission or even recover.

Resistance to Pitch Canker. It is not uncommon to observe Monterey pines that are unaffected by pitch canker, even where they are surrounded by severely infected trees. Monterey pines have a wide range of susceptibility to pitch canker. Resistant Monterey pines can be vegetatively propagated as rooted cuttings, and trees that develop from cuttings of resistant trees retain the resistance of the parent tree.

Resistance may be a useful tool for managing the disease in landscape settings, Christmas tree farms, and in commercial forestry. However, the genetic resistance may be adversely affected by changes in the pathogen population over time. Trees that now appear resistant could become susceptible if more virulent strains of the fungus arise through mutations or genetic recombination (as a result of sexual reproduction) or if new strains of the fungus are introduced from elsewhere in the world.

Though the fungus is primarily spreading by asexual propagation in California, laboratory studies indicate that strains within California have the ability to outcross (reproduce sexually). If outcrossing begins to occur naturally in California, new strains could develop. Furthermore, strains of the fungus isolated both in Mexico and in Florida are able to cause disease on a Monterey pine that is resistant to the eight predominant strains of the fungus in California. Thus, Monterey pines will always be at some risk of future damage from pitch canker, and the use of resistant stock for landscape plantings should be undertaken only if the use of nonsusceptible tree species is not an option.

Preventing Movement of the Pathogen. In order to minimize the damage caused by pitch canker, it is important to prevent movement of the pathogen to noninfested areas. With this in mind, the California Board of Forestry has designated a zone of infestation that includes most of coastal California (see the zone of infestation map on the Pitch Canker Task Force Web site listed in Online Resources). You can also contact the agricultural commissioner in your county to determine whether or not you are within this zone. Local regulations may apply to the movement of potentially infested materials to areas outside the zone of infestation. Because the pathogen can survive in wood cut from infected trees, use or dispose of infected trees locally. The pathogen can also survive in soil, in seed, and can infect seedlings that show no symptoms. Consequently, avoid moving any of these materials into areas where the disease does not already occur. For more information on management of pitch canker, consult the Web site of the Pitch Canker Task Force listed in Online Resources.

MANAGEMENT

As mentioned above, some infected pines do recover, even if they are severely diseased. Pruning does not slow the spread of the disease in a highly infested area. However, pruning can be used strategically to enhance the aesthetic quality of a tree and thereby delay its removal from the landscape. Because trees may recover, their removal should be delayed as long as possible, and only trees that pose a hazard should be cut down. In areas where Monterey pine is not native (most of California outside of Año Nuevo, Cambria, and Monterey), select pines that are resistant to pitch canker (Table 2) or other nonsusceptible trees for replanting.

Table 2. Susceptibility of Some Conifers Grown in California to Pitch Canker Caused by Fusarium circinatum.

Susceptibility

Species

Common name

Status¹

Greenhouse²

Field³

Pinus attenuata

knobcone pine

native

P. canariensis

Canary Island pine

exotic

P. contorta ssp. contorta

shore pine

native

P. contorta ssp. murryana

lodgepole pine

native

P. coulteri

Coulter pine

native

S-

P. eldarica

Eldarica pine

exotic

P. halepensis

Aleppo pine

exotic

P. jeffreyi

Jeffrey pine

native

P. lambertiana

sugar pine

native

P. monophylla

pinyon pine

native

S-

P. muricata

bishop pine

native

P. pinea

Italian stone pine

exotic

P. ponderosa

ponderosa pine

native

S-

P. radiata

Monterey pine

native

P. sabiniana

gray pine

native

S-

P. sylvestris

Scotch pine

exotic

P. thunbergii

Japanese black pine

exotic

P. torreyana

Torrey pine

native

S-

Pseudotsuga menziesii

Douglas fir

native

S-

1	Native species are found in native forests, but may also be grown as timber species (e.g., ponderosa pine) or as landscape trees (e.g. Monterey pine); the exotic species are commonly planted in various parts of the state.
2	Greenhouse tests of susceptibility were based on the results of artificial inoculations. Species are rated as susceptible (S) if they sustained definite lesions at the site of inoculation, or resistant (R) if there was little or no lesion development. For species rated as S-, most tested individuals were resistant, but a small percentage appeared moderately susceptible. NT indicates a species that has not been tested.
3	Field susceptibility is based on observations of natural infections. Species are rated as susceptible (S) if numerous trees are known to be infected and/or some trees have sustained severe damage from pitch canker. Species that have frequently been observed in otherwise infested areas and for which few or no trees are known to have sustained natural infections and none have been heavily damaged by pitch canker are rated as resistant (R); the level of resistance differs within this group. For species rated as S-, one or more infected trees have been observed, but the number of observations is too limited to provide a meaningful estimate of their relative susceptibility. For species rated as N, no infected trees have been observed, but the occurrence of this species in proximity to natural inoculum is too infrequent to conclude that the lack of disease is indicative of resistance.

REFERENCES

Bonello, P., T. R. Gordon, and A. J. Storer. 2001. Systemic induced resistance in Monterey pine. For. Pathol. 31: 1-8.

Gordon T. R., A. J. Storer, and D. L. Wood. 2001. The pitch canker epidemic in California. Plant Disease 85: 1128-1139.

Gordon, T. R., K. R. Wikler, S. L. Clark, D. Okamoto, A. J. Storer, and P. Bonello. 1998. Resistance to pitch canker disease, caused by Fusarium subglutinans f.sp. pini, in Monterey pine (Pinus radiata). Plant Pathol. 47: 706-711.

McCain, A. H., C. S. Koehler, and S. A. Tjosvold. 1987. Pitch canker threatens California pines. Calif. Agric. 41: 22-23.

Storer, A. J., T. R. Gordon, and D. L. Wood. 2002. The epidemiology of pitch canker of Monterey pine in California. For. Sci. 48: 694-700.

Wikler, K. R., and T. R. Gordon. 2000. An initial assessment of genetic relationships among populations of Fusarium circinatum in different parts of the world. Can. J. Bot. 78: 709-717.

Wikler, K. R., T. R. Gordon, S. L. Clark, M. J. Wingfield, and H. Britz. 2000. Potential for outcrossing in an apparently asexual population of Fusarium circinatum, the causal agent of pitch canker. Mycologia 92: 1085-1090.

Wikler, K. R., A. J. Storer, W. Newman, W. Gordon, T. R. Gordon, and D. L. Wood. In press. The dynamics of an introduced pathogen in a native Monterey pine (Pinus radiata) forest. Forest Ecology and Management.

ONLINE RESOURCES

Pitch Canker Task Force Web site

Center for Forestry Pitch Canker Extension Project Web site

PUBLICATION INFORMATION

Pest Notes: Pitch Canker
UC ANR Publication 74107

Authors: K. Wikler, UC Cooperative Extension, Alameda Co.; T. R. Gordon, Plant Pathology, UC Davis; A. J. Storer, Insect Biology, UC Berkeley; and D. L. Wood, Forest Science, UC Berkeley
Editor: B. Ohlendorf
Technical Editor: M. L. Flint
Produced by IPM Education and Publications, University of California Statewide IPM Program

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