Gymnosporangium juniperi-virginianae
Encyclopedia
Gymnosporangium juniperi-virginianae is a plant pathogen that causes cedar-apple rust. In virtually any location where apple
s or crabapples (Malus
) and Eastern red cedar (Juniperus virginiana
) coexist, cedar apple rust can be a destructive or disfiguring disease on both the apples and cedars. Quince
and hawthorn
can substitute for the apples as hosts and many species of juniper
can substitute for the Eastern red cedars.
On the Eastern Red Cedar host, the fungus produces reddish-brown galls from 1/4 to 1 inch in diameter. These galls can be mistaken for cone structures by the uninitiated. After reaching a diameter of about 1/2 inch, they show many small circular depressions. In the center of each depression is a small, pimple-like structure. In the spring these structures elongate into orange gelatinous protrusions or horns. The spore-bearing horns swell during rainy periods in April and May. The wind carries the microscopic spores to infect apple leaves, fruit and young twigs on trees within a radius of several miles of the infected tree.
On other species of juniper more common in landscaping and bonsai, the sizes of the infections are reduced. Early in the infection, the galls are small bumps on the woody portions of the plant. They maintain the orange gelatinous form after the first warm rains of spring but generally on a greatly reduced scale.
or more specifically Gymnosporangium juniperi-virginianae that spend part of their life cycles on Eastern Red Cedars growing near orchards. The complex disease cycle of cedar apple rust, alternating between two host plants, was first delineated by Anders Sandøe Ørsted (botanist)
.
On the eastern seaboard of the United States, at the first warm rain of spring, the spore horns become gelatinous masses and produce their teliospores. Wind carries the spores to apple leaves at about the time that apple buds are in the pink or early blossom stage. Upon reaching apple buds or leaves, the spores attach themselves to the young leaves, germinate, and enter the leaf or fruit tissues. Infection takes place in as little as four hours under favorable conditions. Yellow lesions develop in one to three weeks.
In July and August, spore
s from the apple leaves (Aeciospores) are produced. The wind carries the spores back to Eastern Red Cedars, completing the infectious cycle. The spores land on cedar needle bases or in cracks or crevices of twigs. There, they germinate and producing small, green-brown swellings about the size of a pea. Gall
s do not produce spores until the second spring. However, mature galls usually are present every year. This fungus produces four out of five of the spores known to be produced by the class Urediniomycetes during its life cycle. (Teliospores, Basidiospores, Spermatia, and Aeciospores. The type of spore it does not produce is Urediospores) Rust fungi have a complicated life-cycle with up to five types of spores (each borne on a different type of structure) in its life cycle and often an alternate host, and an "alternate alternate host" as well.
There are differences in the susceptibility of various apple varieties. Jonathan, Rome Beauty, Wealthy and York Imperial are susceptible. Grimes Golden, Red Delicious, Winesap, Staymans, Redfree, Jonafree and Priscilla are resistant. Crabapples are generally more susceptible than apples. Resistant crabapples include Adams, Beverly, Candied Apple, Dolgo, Donald Wyman, Eleyi, Inglis, Indian Summer, Liset, Mt. Arbor, Narangasett, Periscifolia, Red Jewel, Robinson, Robusta, Royalty, Sargent cv., Tina, Snowdrift, and Special Radiant. Resistant Crataegus (Hawthorn) include crus-galli, Intricate, laevigata, Autumn Glory, phaenopyrum, pruinosa, viridis, and Winter King. The resistant varieties are less susceptible to attack, but that does not mean that they are free from an aggressive attack.
Fungicide sprays applied in a timely manner are highly effective against the rust diseases during the apple cycle. Most sprays are applied four times at 7- to 10-day intervals, starting with pink bud on crabapples. These applications are to protect the apples from spores being released from the cedar host in mid-spring.
If cedar apple rust disease is diagnosed on apple fruits and leaves it is far too late to spray. Systemic fungicides are available.
Fungicide
s listed for use on apples can be used in July and August on the cedars to reduce infection. Application of fungicides to the junipers before and while they are in the infectious orange gelatinous state seems to reduce the severity of the outbreak.
Apple
The apple is the pomaceous fruit of the apple tree, species Malus domestica in the rose family . It is one of the most widely cultivated tree fruits, and the most widely known of the many members of genus Malus that are used by humans. Apple grow on small, deciduous trees that blossom in the spring...
s or crabapples (Malus
Malus
Malus , the apples, are a genus of about 30–35 species of small deciduous trees or shrubs in the family Rosaceae. Other studies go as far as 55 species including the domesticated Orchard Apple, or Table apple as it was formerly called...
) and Eastern red cedar (Juniperus virginiana
Juniperus virginiana
Juniperus virginiana is a species of juniper native to eastern North America, from southeastern Canada to the Gulf of Mexico, east of the Great Plains...
) coexist, cedar apple rust can be a destructive or disfiguring disease on both the apples and cedars. Quince
Quince
The quince , or Cydonia oblonga, is the sole member of the genus Cydonia and native to warm-temperate southwest Asia in the Caucasus region...
and hawthorn
Crataegus
Crataegus , commonly called hawthorn or thornapple, is a large genus of shrubs and trees in the rose family, Rosaceae, native to temperate regions of the Northern Hemisphere in Europe, Asia and North America. The name hawthorn was originally applied to the species native to northern Europe,...
can substitute for the apples as hosts and many species of juniper
Juniper
Junipers are coniferous plants in the genus Juniperus of the cypress family Cupressaceae. Depending on taxonomic viewpoint, there are between 50-67 species of juniper, widely distributed throughout the northern hemisphere, from the Arctic, south to tropical Africa in the Old World, and to the...
can substitute for the Eastern red cedars.
Symptoms
On the apple tree, the infections occur on leaves, fruit and young twigs. The brightly colored spots produced on the leaves make it easy to identify. Small, pale yellow spots appear on the upper surfaces of the leaves, usually during late April or May on the eastern seaboard of the United States. These spots gradually enlarge and turn orange or red and may show concentric rings of color. Drops of orange liquid may be visible on the spots. Later in the season, black dots appear on the orange spots on the upper leaf surface. In late summer, tube-like structures develop on the undersurface of the apple leaf. Infected leaves sometimes drop prematurely, particularly during drought conditions or when the tree is under additional stress. Infections on fruit are usually near the blossom end and are somewhat similar to the leaf lesions.On the Eastern Red Cedar host, the fungus produces reddish-brown galls from 1/4 to 1 inch in diameter. These galls can be mistaken for cone structures by the uninitiated. After reaching a diameter of about 1/2 inch, they show many small circular depressions. In the center of each depression is a small, pimple-like structure. In the spring these structures elongate into orange gelatinous protrusions or horns. The spore-bearing horns swell during rainy periods in April and May. The wind carries the microscopic spores to infect apple leaves, fruit and young twigs on trees within a radius of several miles of the infected tree.
On other species of juniper more common in landscaping and bonsai, the sizes of the infections are reduced. Early in the infection, the galls are small bumps on the woody portions of the plant. They maintain the orange gelatinous form after the first warm rains of spring but generally on a greatly reduced scale.
The disease cycle
Understanding of the disease cycle of this rust fungus is necessary for proper identification and control. Cedar apple rust is caused by the fungi GymnosporangiumGymnosporangium
Gymnosporangium is a genus of heteroecious plant-pathogenic fungi which alternately infect members of the family Cupressaceae, primarily species in the genus Juniperus , and members of the family Rosaceae in the subfamily Maloideae...
or more specifically Gymnosporangium juniperi-virginianae that spend part of their life cycles on Eastern Red Cedars growing near orchards. The complex disease cycle of cedar apple rust, alternating between two host plants, was first delineated by Anders Sandøe Ørsted (botanist)
Anders Sandøe Ørsted (botanist)
Anders Sandøe Ørsted, also written as Anders Sandoe Oersted or Anders Sandö Örsted was a Danish botanist, mycologist, zoologist and marine biologist. He was nephew of the brothers physicist H.C...
.
On the eastern seaboard of the United States, at the first warm rain of spring, the spore horns become gelatinous masses and produce their teliospores. Wind carries the spores to apple leaves at about the time that apple buds are in the pink or early blossom stage. Upon reaching apple buds or leaves, the spores attach themselves to the young leaves, germinate, and enter the leaf or fruit tissues. Infection takes place in as little as four hours under favorable conditions. Yellow lesions develop in one to three weeks.
In July and August, spore
Spore
In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...
s from the apple leaves (Aeciospores) are produced. The wind carries the spores back to Eastern Red Cedars, completing the infectious cycle. The spores land on cedar needle bases or in cracks or crevices of twigs. There, they germinate and producing small, green-brown swellings about the size of a pea. Gall
Gall
Galls or cecidia are outgrowths on the surface of lifeforms caused by invasion by other lifeforms, such as parasites or bacterial infection. Plant galls are abnormal outgrowths of plant tissues and can be caused by various parasites, from fungi and bacteria, to insects and mites...
s do not produce spores until the second spring. However, mature galls usually are present every year. This fungus produces four out of five of the spores known to be produced by the class Urediniomycetes during its life cycle. (Teliospores, Basidiospores, Spermatia, and Aeciospores. The type of spore it does not produce is Urediospores) Rust fungi have a complicated life-cycle with up to five types of spores (each borne on a different type of structure) in its life cycle and often an alternate host, and an "alternate alternate host" as well.
Control
Because apples are the economically important crop, control is usually focused there. Interruption of the disease cycle is the only effective method for control of the cedar apple rust. The recommended method of control is to “remove cedars located within a 1-mile radius” of the apples to interrupt the disease cycle, though this method is seldom practical. For those doing bonsai, it is common to have the trees within feet of each other and on the central eastern seaboard of the United States, Eastern Red Cedar is a common first-growth conifer along roadsides.There are differences in the susceptibility of various apple varieties. Jonathan, Rome Beauty, Wealthy and York Imperial are susceptible. Grimes Golden, Red Delicious, Winesap, Staymans, Redfree, Jonafree and Priscilla are resistant. Crabapples are generally more susceptible than apples. Resistant crabapples include Adams, Beverly, Candied Apple, Dolgo, Donald Wyman, Eleyi, Inglis, Indian Summer, Liset, Mt. Arbor, Narangasett, Periscifolia, Red Jewel, Robinson, Robusta, Royalty, Sargent cv., Tina, Snowdrift, and Special Radiant. Resistant Crataegus (Hawthorn) include crus-galli, Intricate, laevigata, Autumn Glory, phaenopyrum, pruinosa, viridis, and Winter King. The resistant varieties are less susceptible to attack, but that does not mean that they are free from an aggressive attack.
Fungicide sprays applied in a timely manner are highly effective against the rust diseases during the apple cycle. Most sprays are applied four times at 7- to 10-day intervals, starting with pink bud on crabapples. These applications are to protect the apples from spores being released from the cedar host in mid-spring.
If cedar apple rust disease is diagnosed on apple fruits and leaves it is far too late to spray. Systemic fungicides are available.
Fungicide
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...
s listed for use on apples can be used in July and August on the cedars to reduce infection. Application of fungicides to the junipers before and while they are in the infectious orange gelatinous state seems to reduce the severity of the outbreak.