Leucostoma kunzei
Encyclopedia
The pathogenic
fungus, Leucostoma kunzei (formerly Valsa kunzei) is the causal agent of Leucostoma
canker (also known as Cytospora
canker or spruce canker) a disease of spruce
trees found in the Northern Hemisphere, predominantly on Norway spruce
(Picea abies) and Colorado blue spruce (Picea pungens). This disease is one of the most common and detrimental stem diseases of Picea species in the northeastern United States, yet it also affects other coniferous species. Rarely does it kill its host tree; however, the disease does disfigure by killing host branches and causing resin
exudation from perennial lesions on branches or trunks.
occurring within a branch or along the mainstem caused by this pathogen. These brown needles will remain attached during the growing season and then fall off during the winter, leaving behind bare twigs and branches. This entire process can occur annually, moving from low branches to higher branches, thus destroying the symmetry of the host tree. Twigs and branches killed by this disease may remain on the diseased host tree for several years. All of this damage caused by this fungal pathogen does not typically begin until the host trees are at least 10-15 years old. However, in landscape nurseries small branches of young blue spruce or occasionally white spruce may be killed.
Lesions typically begin at the bases of small twigs and develop into elliptic or occasionally diamond-shaped cankers. Lesions that originate on branches close to the main stem may actually spread into the main stem. Cambium that has been killed by this disease has a brown to reddish brown internal coloration and is saturated with resins. The underlying sapwood
, which has been killed and colonized by the pathogen, is rarely discolored. Amber colored resin profusely exudes from the edges of cankers, runs down the bark, or drips onto lower branches or the ground, and then hardens into a white crust. The lesions associated with this pathogen typically go visibly unnoticed on infected host trees for several years, due to the diseased tissue being held in place by resin. The formation of callus at canker margins is subtle or nearly absent, usually resin is the only indication of an underlying bark lesion. Cankers formed on the trunk will eventually appear as sunken due to living tissues (callus) expanding and growing around the wounded tissues. Complete girdling of the host trunk or large limbs may occur; however, this event may take several years to even decades to accomplish. In other susceptible conifers, symptoms are similar to those of spruce except resin exudation is usually less prominent. Regarding pines the key symptom to note is the inconspicuous branch cankers caused by this pathogen.
Conidia are released during wet weather conditions of spring, but also throughout summer and autumn. These conidia can withstand freezing temperatures, which aids in survival of this fungus, and conidia germinate at approximately 20-33°C. The optimal temperature for conidial germination and initial growth of the fungus is around 27°C. The ascospores are also released in spring, as well as, early summer. Dispersal of conidiospores and ascospores via running or splashing water provides evidence for the year-to-year intensification and increasing progression of symptoms. Both spore types have also been found dispersed on the wind in the vicinity of diseased trees, yet the means of becoming airborne is still uncertain. There is speculation that this dispersal by air may in fact be due to spore release via rain droplets which become free in air as the droplets evaporate. The conidia are found to be more abundantly dispersed in water and air, in contrast to ascospores. These airborne spores, as well as, insects provide an explanation for the spread of this disease from tree to tree. Once a branch or stem of a susceptible host has been girdled, the pathogen will rapidly colonize large areas of bark beyond the site of girdling. Following this, the pathogen will produce numerous pycnidial and later perithecial stromata. The probable duration of this disease cycle is 1 year, due to pycnidial stromata which form within the first year of lesion enlargement.
Selective pruning of lower branches where possible, without completely destroying the aesthetic appearance of the tree is advisable. On less severely cankered trees, all diseased and adjacent branches should be pruned back to the nearest living lateral branch or the trunk. Weak and injured branches should be cut to the trunk of the tree. On major limbs or trunks the cankered portion may be excised. This may be done by removing all brown, dead tissues, as well as, 1 inch of healthy bark and wood on all sides, cutting to a depth of ¼ inch. Proper sanitization of tools is crucial in prevention of accidental spread of this disease; this may be done by disinfecting them by either swabbing or immersing them in a solution of 70% rubbing alcohol. Pruning during wet conditions can potentially increase incidence of disease spread through pruning wounds; therefore, prune only when the foliage and bark are dry. Severely cankered trees cannot be restored to good health and should be completely removed from the site and if possible, burned to remove the source of inoculum.
To date, there have been no fungicides
which have been able to provide prevention or arrest the development of Leucostoma canker on spruce trees
Pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...
fungus, Leucostoma kunzei (formerly Valsa kunzei) is the causal agent of Leucostoma
Leucostoma
Leucostoma may refer to:* Leucostoma , a fly genus in the family Tachinidae* Leucostoma , a genus of fungi within the Valsaceae family...
canker (also known as Cytospora
Cytospora
Cytospora is a genus of ascomycete fungi. Cytospora species are known as plant pathogens.-External links:*...
canker or spruce canker) a disease of spruce
Spruce
A spruce is a tree of the genus Picea , a genus of about 35 species of coniferous evergreen trees in the Family Pinaceae, found in the northern temperate and boreal regions of the earth. Spruces are large trees, from tall when mature, and can be distinguished by their whorled branches and conical...
trees found in the Northern Hemisphere, predominantly on Norway spruce
Norway Spruce
Norway Spruce is a species of spruce native to Europe. It is also commonly referred to as the European Spruce.- Description :...
(Picea abies) and Colorado blue spruce (Picea pungens). This disease is one of the most common and detrimental stem diseases of Picea species in the northeastern United States, yet it also affects other coniferous species. Rarely does it kill its host tree; however, the disease does disfigure by killing host branches and causing resin
Resin
Resin in the most specific use of the term is a hydrocarbon secretion of many plants, particularly coniferous trees. Resins are valued for their chemical properties and associated uses, such as the production of varnishes, adhesives, and food glazing agents; as an important source of raw materials...
exudation from perennial lesions on branches or trunks.
Origins
Leucostoma keunzei or “Valsa kunzei” (Fr.:Fr) Fr. (conidial state -Cytospora kunzei) was first described by Waterman in 1955,as the causal agent for the branch and stem cankers she observed on Douglas fir. Waterman cultured the fungus from cankered trees from Washington, Pennsylvania, Vermont, New Hampshire, and Massachusetts and provided the first descriptions of the canker and fungus. She also noted cankered trees usually occurred on unfavorable sites or had been weakened by other environmental factors.Susceptible Hosts
- Balsam Fir Abies balsamea
- Fraser Fir Abies fraseri
- European Larch Larix decidua
- Japanese Larch Larix kaempferi
- American Larch Larix laricina
- Norway Spruce Picea abies
- Engelmann Spruce Picea engelmannii
- White Spruce Picea glauca
- Black Spruce Picea mariana
- Caucasian Spruce Picea orientalis
- Colorado Blue Spruce Picea pungens
- Red Spruce Picea rubens
- Jack Pine Pinus banksiana
- Red Pine Pinus resinosa
- Eastern White Pine Pinus strobus
- Bhutan Pine Pinus wallichiana
- Eldar Pine Pinus eldarica
- Douglas-fir Pseudotsuga menziesii
- Western Redcedar Thuja plicataThuja plicataThuja plicata, commonly called Western or pacific red cedar, giant or western arborvitae, giant cedar, or shinglewood, is a species of Thuja, an evergreen coniferous tree in the cypress family Cupressaceae native to western North America...
- Eastern Hemlock Tsuga canadensis
Symptoms
Symptoms of this disease in spruce hosts include dead and dying branches and perennial lesions on the branches and trunk, which exude resins. Older branches (lower on the trees) sustain more damage than younger ones. In spring and early summer the foliage of an infected branches on host trees fade and turns brown, which is an indication of girdlingGirdling
Girdling, also called ring barking or ring-barking, is the complete removal of a strip of bark from around the entire circumference of either a branch or trunk of a woody plant. Girdling results in the death of wood tissues beyond the damage...
occurring within a branch or along the mainstem caused by this pathogen. These brown needles will remain attached during the growing season and then fall off during the winter, leaving behind bare twigs and branches. This entire process can occur annually, moving from low branches to higher branches, thus destroying the symmetry of the host tree. Twigs and branches killed by this disease may remain on the diseased host tree for several years. All of this damage caused by this fungal pathogen does not typically begin until the host trees are at least 10-15 years old. However, in landscape nurseries small branches of young blue spruce or occasionally white spruce may be killed.
Lesions typically begin at the bases of small twigs and develop into elliptic or occasionally diamond-shaped cankers. Lesions that originate on branches close to the main stem may actually spread into the main stem. Cambium that has been killed by this disease has a brown to reddish brown internal coloration and is saturated with resins. The underlying sapwood
Sapwood
Sapwood may refer to:* Sapwood, the part of living wood where sap flows, as distinct from the heartwood, where it doesn't* SS-6 Sapwood, the NATO reporting name for the R-7 Semyorka intercontinental ballistic missile...
, which has been killed and colonized by the pathogen, is rarely discolored. Amber colored resin profusely exudes from the edges of cankers, runs down the bark, or drips onto lower branches or the ground, and then hardens into a white crust. The lesions associated with this pathogen typically go visibly unnoticed on infected host trees for several years, due to the diseased tissue being held in place by resin. The formation of callus at canker margins is subtle or nearly absent, usually resin is the only indication of an underlying bark lesion. Cankers formed on the trunk will eventually appear as sunken due to living tissues (callus) expanding and growing around the wounded tissues. Complete girdling of the host trunk or large limbs may occur; however, this event may take several years to even decades to accomplish. In other susceptible conifers, symptoms are similar to those of spruce except resin exudation is usually less prominent. Regarding pines the key symptom to note is the inconspicuous branch cankers caused by this pathogen.
Conidia are released during wet weather conditions of spring, but also throughout summer and autumn. These conidia can withstand freezing temperatures, which aids in survival of this fungus, and conidia germinate at approximately 20-33°C. The optimal temperature for conidial germination and initial growth of the fungus is around 27°C. The ascospores are also released in spring, as well as, early summer. Dispersal of conidiospores and ascospores via running or splashing water provides evidence for the year-to-year intensification and increasing progression of symptoms. Both spore types have also been found dispersed on the wind in the vicinity of diseased trees, yet the means of becoming airborne is still uncertain. There is speculation that this dispersal by air may in fact be due to spore release via rain droplets which become free in air as the droplets evaporate. The conidia are found to be more abundantly dispersed in water and air, in contrast to ascospores. These airborne spores, as well as, insects provide an explanation for the spread of this disease from tree to tree. Once a branch or stem of a susceptible host has been girdled, the pathogen will rapidly colonize large areas of bark beyond the site of girdling. Following this, the pathogen will produce numerous pycnidial and later perithecial stromata. The probable duration of this disease cycle is 1 year, due to pycnidial stromata which form within the first year of lesion enlargement.
Disease Management
Due to older, weakened trees being most susceptible to Leucostoma kunzei, the key factor in proper management of this disease is maintenance of tree health and vigor by reducing stress on the tree. Choose planting sites with good, moist, well-drained soils; avoid shallow or excessively drained soils. During periods of prolonged drought or on dry sites regular watering is important during the growing season, as well as, the application of fertilizers every few years. Well-established trees and avoidance of any disturbance to the root system that may result in root injury or poor root growth both reduce likelihood of individual trees becoming diseased.Selective pruning of lower branches where possible, without completely destroying the aesthetic appearance of the tree is advisable. On less severely cankered trees, all diseased and adjacent branches should be pruned back to the nearest living lateral branch or the trunk. Weak and injured branches should be cut to the trunk of the tree. On major limbs or trunks the cankered portion may be excised. This may be done by removing all brown, dead tissues, as well as, 1 inch of healthy bark and wood on all sides, cutting to a depth of ¼ inch. Proper sanitization of tools is crucial in prevention of accidental spread of this disease; this may be done by disinfecting them by either swabbing or immersing them in a solution of 70% rubbing alcohol. Pruning during wet conditions can potentially increase incidence of disease spread through pruning wounds; therefore, prune only when the foliage and bark are dry. Severely cankered trees cannot be restored to good health and should be completely removed from the site and if possible, burned to remove the source of inoculum.
To date, there have been no fungicides
Fungicide
Fungicides are chemical compounds or biological organisms used to kill or inhibit fungi or fungal spores. Fungi can cause serious damage in agriculture, resulting in critical losses of yield, quality and profit. Fungicides are used both in agriculture and to fight fungal infections in animals...
which have been able to provide prevention or arrest the development of Leucostoma canker on spruce trees
Suggested Replacement Species (Hardiness Varieties)
- Siberian Spruce Picea omorika
- Blue Atlas Cedar Cedrus atlantica
- Nikko Fir Abies homolepis
- Leyland Cypress Cupressus leylandii
- Chinese Juniper Juniperus chinensisJuniperus chinensisJuniperus chinensis grows as a shrub or tree with a very variable in shape, reaching 1-20 m tall. This native of northeast Asia grows in China, Mongolia, Japan, Korea and the southeast of Russia.-Growth:...
- Rocky Mountain Juniper Juniperus scopulorumJuniperus scopulorumJuniperus scopulorum is a species of juniper native to western North America, in Canada in British Columbia and southwest Alberta, in the United States from Washington east to North Dakota, south to Arizona and also locally western Texas, and northernmost Mexico from Sonora east to Coahuila...
- Japanese Cedar Cryptomeria japonica