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Categorization of Damage of Fungal Diseases: Severe to Moderate
The differences between white, brown, and sapwood rot fungi can be characterized by how they decompose trees, the symptoms that may be present as a result of the infection, and the severity of damage.
White rot fungi: fungal hyphae, or the root-like structures of fungus, decompose all parts of the cell, including lignin (a substance in plants that is resistant to most types of decay (1)). Early stages of white rot fungi damage are usually not visible and can be categorized as moderate to severe. Severity of decay depends on the species of fungus, the species of plant infected, and duration of infection. Although this particular type of decay can be severe, because of the slow progression of the fungal mycelium (the fungal hyphae as a whole) most trees are able to maintain function and structure through compartmentalization, a growth response that functions by blocking the pathogen from further growing into the tree, and naturally growing new wood around the infection. (4) Figure 1 is an example of white rot.
( Figure one: an example of white rot fungi growing on a dead log) (11)
Brown rot fungi: decays the carbohydrates in the cell wall of tree cells leaving an abundance of lignin behind. Effects of brown rot occur rapidly and can often times be seen with the naked eye. Because the onset of brown rot infection quickly weakens the structural integrity of woody material, damage can often times be categorized as severe (1) and by many arborists, is considered the most severe form of decay because of its rapid onset that usually affects more of a tree than is immediately noticeable (4). The affects of the fungi that are not immediately noticeable are due to the removal of cellulose from the tree’s tissue. This removal of cellulose reduces the tree’s ability to bend without structural failure occurring. Figure 2 below shows a telephone pole that is infected with brown rot fungi.
Although brown rot fungi does not usually kill a tree, it is considered a severe infection because of its ability to destroy the structural integrity of trees. As a trees structural integrity decreases, its risk (considering human safety and damage to cars or buildings) increases. Brown rot fungi can also spread from an infected tree to a non-infected tree when wind or rain water carries the spores to a suitable host (12). Some of the management strategies to reduce the impact of brown rot fungi include pruning four to six inches below sunken or dead tissue on a branch; burning the infected branches (if legal), and cleaning pruning supplies in between each tree or after pruning a site known to be infected with 70% rubbing alcohol solution.
If the sapwood of a tree is known to be infected with brown rot fungi, then an advanced assessment of the tree should be completed or the tree should be removed because this would greatly increase the risk of the tree.
Although brown rot fungi does not usually kill a tree, it is considered a severe infection because of its ability to destroy the structural integrity of trees. As a trees structural integrity decreases, its risk (considering human safety and damage to cars or buildings) increases. Brown rot fungi can also spread from an infected tree to a non-infected tree when wind or rain water carries the spores to a suitable host (12). Some of the management strategies to reduce the impact of brown rot fungi include pruning four to six inches below sunken or dead tissue on a branch; burning the infected branches (if legal), and cleaning pruning supplies in between each tree or after pruning a site known to be infected with 70% rubbing alcohol solution.
If the sapwood of a tree is known to be infected with brown rot fungi, then an advanced assessment of the tree should be completed or the tree should be removed because this would greatly increase the risk of the tree.
(Photo above is referenced in row 4 of works cited)
Erwinia spp: a genus of bacteria that cause cankers, leaf spots, wilts, blights, discoloration, die back, fruit collapse, stalk rot, crown rot, and stem rot (2). Because symptoms of Erwinia (commonly known as fireblight) can be present in many different forms, it can be difficult to diagnose the disease. If a tree is suspected to be infected with any form of an Erwinia species pathogen, it is suggested to call a local plant health inspector who specializes in tree diseases to inspect the tree (5). If a plant health inspector identifies that Erwinia spp. may be present, they may suggest taking samples of the plant material that appear to be infected to a lab for an accurate diagnosis (5). Some of the most common plants affected by fireblight are plants in the rosaceae family (which includes apples and roses) (5). Although many symptoms may be present due to fireblight, one common symptom, more easily identified by homeowners, is that an infected plant may look burned. This feature of the disease’s symptoms includes black tipped and curled stems and leaves. The following pictures are damage caused by fireblight:
(photo above referenced in row 6 of works cited)
(photo above referenced in column 7 of works cited)
Oak wilt: caused by the fungus Ceratocystis fagacearum is a severely damaging and deadly disease of many oak species (3).
Oak wilt is transmitted by picnic beetles (nitidulid beetle) which are attracted to the wounds of oaks (may also be transmitted from root grafts of infected oaks to new hosts) (8). Many oaks are annually wounded by storm damage, lawn mowers, and pruning. It is these regular damages that are suspected of predisposing a tree to oak wilt.
All Oak species show signs of oak wilt by browning of the leaf tips and flag poling. The browning of leaves due to this infection progresses inward. Flag poling is a symptom of the disease that occurs when a whole section of the tree its off individually. A picture representing flag poling is represented below, on the left. If a tree is suspected of oak wilt, a local plant disease expert should be called immediately. If the tree is confirmed to have oak wilt disease, the tree needs to be removed in order to prevent the infection from spreading. There is no known cure for oak wilt disease (8).
Oak wilt infestation is categorized as severely damaging because it usually results in the death of the infected tree (3).
Oak wilt is transmitted by picnic beetles (nitidulid beetle) which are attracted to the wounds of oaks (may also be transmitted from root grafts of infected oaks to new hosts) (8). Many oaks are annually wounded by storm damage, lawn mowers, and pruning. It is these regular damages that are suspected of predisposing a tree to oak wilt.
All Oak species show signs of oak wilt by browning of the leaf tips and flag poling. The browning of leaves due to this infection progresses inward. Flag poling is a symptom of the disease that occurs when a whole section of the tree its off individually. A picture representing flag poling is represented below, on the left. If a tree is suspected of oak wilt, a local plant disease expert should be called immediately. If the tree is confirmed to have oak wilt disease, the tree needs to be removed in order to prevent the infection from spreading. There is no known cure for oak wilt disease (8).
Oak wilt infestation is categorized as severely damaging because it usually results in the death of the infected tree (3).
(Photo above cited in row 13 or references)
REFERENCES
- Microorganisms causing decay in trees and wood. Blanchette, R. 2006, Research Projects/University of Minnesota.
- ERWINIA. Hardy Diagnostics. 1996-2016
- Identify, Prevent, and Control Oak Wilt. O’brien, J; Mielke, M; Starkey, D; Juzwik J. United States department of Agriculture. August, 2011. pp. 1-30
- Wood Decay in Living and Dead Trees: A Pictorial Overview, Walter C. Shortle; Kenneth R Dudzik. United States Department of Agriculture. July 26th, 2011
- Frequently Asked Questions about Firerblight. Finnish food safety Evira. 12.8.2016. Evira
- Fire blight on ‘Chenango Strawberry’ apple trees. David Rosenberger. Tree Fruit Diseases: Observations and Archives. blogs.cornell.edu/plantpath. May 28, 2014.
- Fire Blight. Extension Utah State University; University Idaho Extension; Colorado State University Extension. Utah State University copyright. intermountainfruit.org. Intermountain Tree Fruit Production Guide.
- Oak Wilt: A Threat to Red Oaks and White Oaks species. The Tree Doctor (aka The Plant Doctor). Michigan State University. treedoctor.msu.edu/oakwilt.
- Oak wilt: Diagnosing and preventing. Bob Bricault. Michigan State University Extension. msue.anr.msu.edu/news/oak_wilt-diagnosing_and_preventing. July 28th, 2014.
- Oak > Leaves > Leaf edges brown, center of leaf green. Oak wilt Ceratocystis fagacearum. University of Minnesota Extension. www.extension.umn.edu/garden/diagnose/plant/deciduous/oak/brownleavesedge
- Wood Rots in Apple Trees. Alan R. Briggs- West Virginia University. Cooperative extension. articles.extension.org. 2018.
- Brown rot. Ashley Ellinghuysen. University of Wisconsin-Extension. hort.uwex.edu/articles/brown-rot/
- Oak wilt disease on an oak tree. Joseph O’Brien. USDA Forest Service, Bugwood.org