Oak wilt
Encyclopedia
Oak wilt is a fungal disease
that can quickly kill an oak
tree. It is caused by the fungus Ceratocystis fagacearum. Symptoms vary by tree species but generally consist of leaf discoloration, wilt, defoliation, and death. The fungus is spread from diseased to healthy trees by insect vectors or via connections between tree roots. Management of the disease consists mainly of preventing infection by avoiding tree wounds, removing diseased trees and digging trenches that disrupt root connections. Chemical treatments are available and are mostly preventative as well. Oak wilt is an important disease of oak for timber production and of oak trees in urban areas.
, northern red
, northern pin
and others with pointed leaf edges are particularly susceptible and, when infected, generally die over the course of a single summer. Infected red oak wilt from the top of the tree down as leaves become a bronze color and fall off the tree. Another symptom is discoloration of the vascular tissues. Brown streaks or spots can be seen under the bark in the sapwood.
Oaks in the white oak group (white
, swamp white
, bur
and others with rounded leaf edges) are somewhat less susceptible when infected (White Oak in particular) and can live for several years after infection, losing a few branches each season, from the top down. Some types of white oak, such as Bur Oak, are more susceptible than others, although not as susceptible as red oaks. Symptoms in white oak are similar to those in red oak.
Oaks with oak wilt stand out with their dead crown compared to a green canopy in the summer, so much so that oak wilt infections can be spotted from the air.
Live oak
susceptibility is somewhat variable depending on environmental conditions but wilt and death usually occur within six months of infection. Live oak foliar symptoms differ from those of red and white oak. Infected live oak leaves develop chlorotic veins that eventually turn necrotic before falling off the tree.
. After a tree has wilted and died, if conditions are right, spores are produced on fungal mats that form under the bark of the tree. These mats produce asexual spores called endoconidia, which are barrel shaped spores produced in chains. If compatible mating types are present, these mats will also produce sexual spores called ascospores in fruiting structures called perithecia. Certain species of sap beetles are attracted to the fruity smell of these mats. They will visit the mats to feed and breed, thereby picking up the fungal spores. These same beetles are also attracted to the bleeding sap
of wounded oak trees and can then deposit the spores picked up from the fungal mats. This method of transmission is important for introducing the fungus into a new area it could not have reached by transmission via root grafts.
Transmission via root graft is the most common means of spread, as trees within as much as 15 m (50 feet) of a diseased tree can be infected. Oak wilt usually moves from diseased trees to healthy trees through roots that have become interconnected (root grafts
). In this case, spores (also endoconidia) that have been produced inside the tree travel through the vascular tissue. Most root grafts form between oaks of the same species; red oak roots graft more commonly than do white oak roots, and grafts between red and white oaks are very rare. Although possible, it is rare for oak wilt to jump between oaks of different species via root grafting – different species do not graft often, and so contaminate each other less frequently.
but more controllable. Beetles that carry the oak wilt fungus do not have chewing mouth parts -and need some other creature or physical damage to create open wounds -whereas beetles that carry dutch elm disease DO Have Chewing mouth parts. Prevention is key, as there is no permanent cure. To prevent beetle transmission, oaks should never be pruned
in the spring
months in the east and Midwest or February through June in Texas. Care should be taken to prevent injury to susceptible trees during this period, particularly from construction. If a tree is injured through a storm or accident in the spring, tree paint
to cover the wound is advised. Reducing the source of spores is helpful. When an oak has died from oak wilt, trees should be debarked, split or chipped then burned or covered with plastic sheeting to effect composting. Heat from composting should destroy or severely enervate the fungus. Logs from trees infected with oak wilt should never be moved to unaffected areas, even for firewood.
If infection is discovered in a tree, a trench (or better yet, two generally parallel trenches at different distances from the area of risk) may be dug to a minimum depth of four feet (ca. 1.2 meters) between it and other potentially susceptible species to prevent root graft disease transmission. Such trenching will sever root grafts that may transmit the disease to neighboring trees. An infected tree should not be immediately cut down lest the oak wilt migrate down into the roots and increase the risk of passing via roots to nearby trees.Injections of propiconazole
can help prevent transmission as well; as many as a half dozen injections every six months may be required to protect a large red oak near infected trees. Injections every other year may also be used to treat a white oak, if it is not yet greatly affected.
, balloon-like outgrowths of the vessels' cell walls that can function to wall-off pathogens and prevent infections from spreading. Fed oaks appear to lack a host-response mechanism that restricts the pathogen's movement, and infection usually kills the tree death by wilting the entire crown. White oaks, which produce tyloses more quickly and in greater numbers, are more resistant to the disease, though the exact mechanism for this resistance is unknown.
or South America
, or Mexico
. The disease currently affects much of the eastern and central US, from Virginia
to Minnesota
to Arkansas
, with pockets of infection as far southwestward as Austin, Texas
. One area of infection has recently been discovered as far northeastward as Glenville, New York
. It is particularly common in the [Midwest
].
Disease
A disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune...
that can quickly kill an oak
Oak
An oak is a tree or shrub in the genus Quercus , of which about 600 species exist. "Oak" may also appear in the names of species in related genera, notably Lithocarpus...
tree. It is caused by the fungus Ceratocystis fagacearum. Symptoms vary by tree species but generally consist of leaf discoloration, wilt, defoliation, and death. The fungus is spread from diseased to healthy trees by insect vectors or via connections between tree roots. Management of the disease consists mainly of preventing infection by avoiding tree wounds, removing diseased trees and digging trenches that disrupt root connections. Chemical treatments are available and are mostly preventative as well. Oak wilt is an important disease of oak for timber production and of oak trees in urban areas.
Hosts and symptoms
Oak wilt affects all oak species, but affects different groups differently. Oaks in the red oak group (blackBlack oak
Quercus velutina, the eastern black oak or more commonly known as simply black oak, is an oak in the red oak group of oaks. It is native to eastern North America from southern Ontario south to northern Florida and southern Maine west to northeastern Texas...
, northern red
Northern Red Oak
Quercus rubra, commonly called northern red oak or champion oak, , is an oak in the red oak group . It is a native of North America, in the northeastern United States and southeast Canada...
, northern pin
Northern Pin Oak
Quercus ellipsoidalis, the Northern Pin Oak or Hill's Oak, is an oak in the red oak section Quercus sect. Lobatae. It is mainly native to the northern midwest United States, and also in the southeast and southwest of Ontario, Canada. It occurs on dry, sandy, usually acidic soils. Although the name...
and others with pointed leaf edges are particularly susceptible and, when infected, generally die over the course of a single summer. Infected red oak wilt from the top of the tree down as leaves become a bronze color and fall off the tree. Another symptom is discoloration of the vascular tissues. Brown streaks or spots can be seen under the bark in the sapwood.
Oaks in the white oak group (white
White Oak
White Oak may refer to:* Quercus alba, a species commonly known as the White Oak* any of various trees from the botanical section Quercus within the list of Quercus species* a 1921 silent western written/produced by and starring William S...
, swamp white
Swamp White Oak
Quercus bicolor, the swamp white oak, is a medium-sized tree of the north central and northeastern mixed forests. It has a very large range, and can survive in a variety of habitats. It grows rapidly and can reach 300 to 350 years...
, bur
Bur oak
Quercus macrocarpa, the Bur Oak, sometimes spelled Burr Oak, is a species of oak in the white oak section Quercus sect. Quercus, native to North America in the eastern and midwestern United States and south-central Canada...
and others with rounded leaf edges) are somewhat less susceptible when infected (White Oak in particular) and can live for several years after infection, losing a few branches each season, from the top down. Some types of white oak, such as Bur Oak, are more susceptible than others, although not as susceptible as red oaks. Symptoms in white oak are similar to those in red oak.
Oaks with oak wilt stand out with their dead crown compared to a green canopy in the summer, so much so that oak wilt infections can be spotted from the air.
Live oak
Live Oak
Live Oak may refer to:*The live oak, any of several types of oak trees that have evergreen foliage.Localities in the United States:* Live Oak, Santa Cruz County, California, a Census-designated place...
susceptibility is somewhat variable depending on environmental conditions but wilt and death usually occur within six months of infection. Live oak foliar symptoms differ from those of red and white oak. Infected live oak leaves develop chlorotic veins that eventually turn necrotic before falling off the tree.
Disease Cycle
The oak wilt fungus spreads in two basic ways: transfer of spores from diseased to healthy trees by insect vectors and movement of the fungus from a diseased tree to a healthy three through root graftsGrafting
Grafting is a horticultural technique whereby tissues from one plant are inserted into those of another so that the two sets of vascular tissues may join together. This vascular joining is called inosculation...
. After a tree has wilted and died, if conditions are right, spores are produced on fungal mats that form under the bark of the tree. These mats produce asexual spores called endoconidia, which are barrel shaped spores produced in chains. If compatible mating types are present, these mats will also produce sexual spores called ascospores in fruiting structures called perithecia. Certain species of sap beetles are attracted to the fruity smell of these mats. They will visit the mats to feed and breed, thereby picking up the fungal spores. These same beetles are also attracted to the bleeding sap
Sap
Sap may refer to:* Plant sap, the fluid transported in xylem cells or phloem sieve tube elements of a plant* Sap , a village in the Dunajská Streda District of Slovakia...
of wounded oak trees and can then deposit the spores picked up from the fungal mats. This method of transmission is important for introducing the fungus into a new area it could not have reached by transmission via root grafts.
Transmission via root graft is the most common means of spread, as trees within as much as 15 m (50 feet) of a diseased tree can be infected. Oak wilt usually moves from diseased trees to healthy trees through roots that have become interconnected (root grafts
Grafting
Grafting is a horticultural technique whereby tissues from one plant are inserted into those of another so that the two sets of vascular tissues may join together. This vascular joining is called inosculation...
). In this case, spores (also endoconidia) that have been produced inside the tree travel through the vascular tissue. Most root grafts form between oaks of the same species; red oak roots graft more commonly than do white oak roots, and grafts between red and white oaks are very rare. Although possible, it is rare for oak wilt to jump between oaks of different species via root grafting – different species do not graft often, and so contaminate each other less frequently.
Environment
In the Midwest and eastern United States, conditions are usually favorable for spore production and beetle activity in spring and early summer. In Texas, mat formation is most common in late fall and winter.Frequency of root graft formation, and therefore root graft transmission, is affected by soil type and stand composition (diversity of tree species).See disease cycle and management sections for details.Management
Oak wilt is similar to Dutch elm diseaseDutch elm disease
Dutch elm disease is a disease caused by a member of the sac fungi category, affecting elm trees which is spread by the elm bark beetle. Although believed to be originally native to Asia, the disease has been accidentally introduced into America and Europe, where it has devastated native...
but more controllable. Beetles that carry the oak wilt fungus do not have chewing mouth parts -and need some other creature or physical damage to create open wounds -whereas beetles that carry dutch elm disease DO Have Chewing mouth parts. Prevention is key, as there is no permanent cure. To prevent beetle transmission, oaks should never be pruned
Pruning
Pruning is a horticultural practice involving the selective removal of parts of a plant, such as branches, buds, or roots. Reasons to prune plants include deadwood removal, shaping , improving or maintaining health, reducing risk from falling branches, preparing nursery specimens for...
in the spring
Spring (season)
Spring is one of the four temperate seasons, the transition period between winter and summer. Spring and "springtime" refer to the season, and broadly to ideas of rebirth, renewal and regrowth. The specific definition of the exact timing of "spring" varies according to local climate, cultures and...
months in the east and Midwest or February through June in Texas. Care should be taken to prevent injury to susceptible trees during this period, particularly from construction. If a tree is injured through a storm or accident in the spring, tree paint
Tree paint
Tree paint, also known as wound dressing, is any substance applied to damaged surfaces of a tree intended to improve the health of the tree. It is commonly applied after pruning, or at locations where the tree bark has been damaged.-Description:...
to cover the wound is advised. Reducing the source of spores is helpful. When an oak has died from oak wilt, trees should be debarked, split or chipped then burned or covered with plastic sheeting to effect composting. Heat from composting should destroy or severely enervate the fungus. Logs from trees infected with oak wilt should never be moved to unaffected areas, even for firewood.
If infection is discovered in a tree, a trench (or better yet, two generally parallel trenches at different distances from the area of risk) may be dug to a minimum depth of four feet (ca. 1.2 meters) between it and other potentially susceptible species to prevent root graft disease transmission. Such trenching will sever root grafts that may transmit the disease to neighboring trees. An infected tree should not be immediately cut down lest the oak wilt migrate down into the roots and increase the risk of passing via roots to nearby trees.Injections of propiconazole
Propiconazole
Propiconazole is a triazole fungicide, also known as a DMI, or demethylation inhibiting fungicide due to its binding with and inhibiting the 14-alpha demethylase enzyme from demethylating a precursor to ergosterol. Without this demethylation step, the ergosterols are not incorporated into the...
can help prevent transmission as well; as many as a half dozen injections every six months may be required to protect a large red oak near infected trees. Injections every other year may also be used to treat a white oak, if it is not yet greatly affected.
Importance
Oak wilt is a devastating disease killing trees rapidly in a single season. It is an important disease in urban areas where a few oak trees in a homeowner's yard may be of great value. If one tree in the homeowners yard becomes infected it will die. Not only will the homeowner need to pay to remove the dead tree, they will also need to protect the rest of the oak trees in their yard or face the prospect that nearby trees in their yard will continue to die. Loss of trees from a property can also lead to a decrease in property value. Even if a homeowner is vigilant about pruning at the correct time, storms and construction can damage trees and introduce oak wilt into a neighborhood. In forest systems, oak wilt is an important disease of oak produced for timber.Host-Parasite Interaction
Hardwood vascular wilt diseases are characterized by blockage of the tree's water-conducting vessels by either the physical presence of the pathogen (mycelium and spores), or through the host's own response to infection. Oak trees, in response to wounding or infection often produce tylosesTylosis
Tylosis may refer to:In medicine:* Diffuse nonepidermolytic palmoplantar keratoderma* Howel–Evans syndromeIn botany:*Occlusion in the xylem of woody plants as response to injury or as protection from decay in heartwood. See CODIT and Tylosis ....
, balloon-like outgrowths of the vessels' cell walls that can function to wall-off pathogens and prevent infections from spreading. Fed oaks appear to lack a host-response mechanism that restricts the pathogen's movement, and infection usually kills the tree death by wilting the entire crown. White oaks, which produce tyloses more quickly and in greater numbers, are more resistant to the disease, though the exact mechanism for this resistance is unknown.
Origin
The causal agent, Ceratocystis fagacearum, is found only within the borders of the United States, but the origin of the pathogen is not known. Recent evidence suggests that the pathogen was introduced into the United States, possibly from CentralCentral America
Central America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. When considered part of the unified continental model, it is considered a subcontinent...
or South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
, or Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
. The disease currently affects much of the eastern and central US, from Virginia
Virginia
The Commonwealth of Virginia , is a U.S. state on the Atlantic Coast of the Southern United States. Virginia is nicknamed the "Old Dominion" and sometimes the "Mother of Presidents" after the eight U.S. presidents born there...
to Minnesota
Minnesota
Minnesota is a U.S. state located in the Midwestern United States. The twelfth largest state of the U.S., it is the twenty-first most populous, with 5.3 million residents. Minnesota was carved out of the eastern half of the Minnesota Territory and admitted to the Union as the thirty-second state...
to Arkansas
Arkansas
Arkansas is a state located in the southern region of the United States. Its name is an Algonquian name of the Quapaw Indians. Arkansas shares borders with six states , and its eastern border is largely defined by the Mississippi River...
, with pockets of infection as far southwestward as Austin, Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...
. One area of infection has recently been discovered as far northeastward as Glenville, New York
New York
New York is a state in the Northeastern region of the United States. It is the nation's third most populous state. New York is bordered by New Jersey and Pennsylvania to the south, and by Connecticut, Massachusetts and Vermont to the east...
. It is particularly common in the [Midwest
Midwestern United States
The Midwestern United States is one of the four U.S. geographic regions defined by the United States Census Bureau, providing an official definition of the American Midwest....
].