What is Black Knot?
Black Knot, caused by the fungus Apiosporina morbosa, is a very common disease of plants in the genus Prunus (See Table 1). A survey in Alberta revealed a significant and widespread distribution of Black Knot found in commercial, municipal, private and natural plantings. This disease reduces the aesthetic value of affected specimens, as infections spread rapidly; high levels may result in the eventual death of the plant.
Table 1: Plant Species Affected by Black Knot
|Amur Cherry||Mayday Tree|
|Black Cherry||Nanking Cherry|
|Dropmore Cherry||Cultivated Plum|
|Flowering Almond||Wild Plum|
|Flowering Plum||Prunus Hybrids|
|Japanese Plum||Sand Cherry|
|Korean Cherry||Sour Cherry|
How can you recognize Black Knot?
The most distinguishing symptom of Black Knot is the characteristic black, tar-like swellings that develop on branches of the infected plant.
Photo Credit: Tricia Simon
Initially, a small, olive-green gall or swelling will develop at a succulent growing point or fruit spur (as a result of spores landing and infection taking place). This swelling will grow until it is mature after 2-3 years. The mature galls are hard, black, 10 to 15 cm (4 to 6 inches) and may be somewhat ruptured. Mature galls will produce and release a vast amount of spores during the bloom period, resulting in a rapid increase in infections. The fungus continues to grow internally and externally, with the branch eventually becoming girdled and dying.
What can be done to control Black Knot?
- Removal of sources of inoculum (prevents population build up)
- Prune out all knot-bearing branches during late fall, winter or very early spring when plants are dormant and knots are easy to see
- Remove infected branches to at least 15-20 cm (6-8 inches) below knot. NOTE: It is preferable to prune an infected branch further back to an appropriate location, such as a healthy collar, rather than leave a stub
- As a precaution, cutting blades should be cleaned and disinfected after pruning, if possible, especially if cuts have been made through obviously infected material
- For knots on scaffold branches or trunks that can’t be removed, cut away diseased tissue down to good wood and at least 1 cm (1/2 inch) beyond the edge of the knot
- Failure to remove branches beyond the internal growth will result in re-growth of the fungus
- DISEASED WOOD MUST BE DESTROYED IMMEDIATELY (burned, buried or removed from site). Diseased knots can produce and release spores for up to 4 months after removal. Proper composting can help to accelerate the breakdown of infected materials
- Ensure plants are healthy and free from stress(not a guarantee from disease)
- Regular monitoring
- Ensure adequate canopy ventilation through proper pruning
- Chemical control (preventative not curative)
- Few choices available
- Not usually recommended unless for valuable plantings, such as collections, orchards, arboreta or for severe infestations
- Other options
- May include use of more resistant selections, ensuring adequate buffer zones between plantings and wild stock, or potential employing biological control products (limited)
- Consider hiring a trained professional for pruning activities (Find a Certified Arborist)
Black Knot of Plums
Tree Fruit and Berry Pathology
Horticulture Tips: Black Knot
- Black Gum Tree Diseases
- Botryosphaeria Canker
- Black Leaf Spot
- Heart Rot
- Tupelo (Nyssa sylvatica) photo: John Hagstrom
- Tree & Plant Care
- Disease, pests, and problems
- Disease, pest, and problem resistance
- Native geographic location and habitat
- Bark color and texture
- Leaf or needle arrangement, size, shape, and texture
- Flower arrangement, shape, and size
- Fruit, cone, nut, and seed descriptions
- Cultivars and their differences
- Cherry tree peeling
- Blight Killing Branches on Flowering Cherry Trees
- Cankers on cherry trees may be black knot fungus
Black Gum Tree Diseases
black water image by Alistair Dick from Fotolia.com
The black gum tree is a shade tree native to North America and hardy to United States Department of Agriculture Plant Hardiness Zones 4b through 9. Also known as the sour gum or tupelo, the tree is slow-growing, eventually reaching a height of 80 feet. The dark gray bark is smooth when immature, becoming cracked as the tree ages. The leaves are elliptical ovals and green during the growing season. In the fall, the leaves turn yellow, orange, red and burgundy. The black gum is susceptible to fungal diseases including botryosphaeria canker, leaf spot infections and heart rot infections.
Botryosphaeria canker is caused by the fungus of the same name, according to the Virginia Tech Cooperative Extension. The fungus attacks trees that are stressed, so prevention is key to keeping black gum trees healthy. The symptoms include branch wilt and dieback. In extreme cases, the bark peels away, revealing discolored underbark. Cankers that look like wounds may appear on branches. These wounds ooze gum from the interior of the tree. The fungi attack trees through pruning wounds, cracks in the bark or naturally occurring pores in the leaves. There is no treatment. Prevent the disease by providing adequate fertilizer and water; plant only healthy black gum trees. Remove and destroy any dead branches.
Black Leaf Spot
Black leaf spot is one of several leaf spot diseases caused by fungus. These leaf spot diseases affect all shade trees, including the black gum tree, according to the University of Illinois Extension. The symptoms include raised, black spots with ragged edges on leaves. Leaf spots multiply at the end of the growing season. In severe cases, the leaves change color, wither and can drop prematurely from the tree. The disease is mostly cosmetic, although if black leaf spot appears in consecutive years, trees can become weakened, making them vulnerable to other diseases and pest infestation. Prevent the disease by practicing good habits such as regular watering and fertilizing the tree to keep it healthy.
Black gum trees are susceptible to heart rot fungal disease in which the heartwood and limbs decay from the inside out. There are several fungi that cause this disease, according to the University of California. Oak root fungus causes a white rot that appears between the bark and the underbark. This fungus enters the black gum tree through the root system. Artist’s conk is a fungus that enters the tree through wounds or openings in the bark. Rings, or conks, form on the bark near the ground. Varnish fungus rot is a slow moving white fungus that attacks the roots and trunk of black gum trees.
Prevent heart rot disease by keeping black gum trees healthy through regular fertilizing and watering. Use proper pruning techniques, such as pruning outside the ridge of the branch bark and .leaving a collar of wood that can heal.
Tupelo (Nyssa sylvatica) photo: John Hagstrom
Tree & Plant Care
Prefers moist, well-drained, acidic soils high in organic matter. Best in full sun.
Tree has a taproot, making it difficult to transplant, spring plant only.
Prune in late fall or during dormant season.
Disease, pests, and problems
Can develop chlorotic (yellowing) leaves in high pH soils.
Cankers and leaf spots are potential problems.
Disease, pest, and problem resistance
Tolerant of black walnut toxicity.
Native geographic location and habitat
Native to eastern North America from New England and southern Ontario south to central Florida and eastern Texas, as well as Mexico.
Found naturally growing on or above stream and ravine banks.
Bark color and texture
Distinct horizontal branching, mature bark has thick blocky ridges, similar to alligator skin.
Leaf or needle arrangement, size, shape, and texture
Alternate, dense leathery leaves are up to 5 inches long, dark green and elliptical in shape with smooth margins. Fall color is scarlet.
Flower arrangement, shape, and size
Dioecious (separate male and female trees), but sometimes each tree has some perfect flowers. Female trees need a male tree for pollination.
Small, greenish-white flowers appear on long stalks the same time leaves are emerging.
Female flowers in sparse clusters and male flowers in dense heads.
Fruit, cone, nut, and seed descriptions
Small, 1/2 inch, dark purple oval fruits (drupes) appears on female trees only.They are quite sour, hence the name.
Fruit ripens ripens in late September as leaves are changing color.
Cultivars and their differences
Afterburner® tupelo (Nyssa sylvatica ‘David Odum’): This cultivar grows 35 feet high and 20 feet wide. Very symmetrical shape (upright pyramidal to oval); excellent red fall color.
Wildfire tupelo (Nyssa sylvatica ‘Wildfire’): New foliage emerges bright red, then matures to a dark, glossy green. Fall color is yellow-orange to purple-red.
Black-gum is the only species of the genus Nyssa that is native to Canada.
Derivation of names
The reasons behind both the scientific and common names for this species are somewhat obscure. Although called black-gum, it produces no gum. The alternative name is black tupelo; tupelo is derived from the indigenous Creek words eto opelwu, which mean swamp tree because this tree often grows in wet and swampy sites. The genus name Nyssa may also allude to the tree’s natural wet habitat. It is named for Mount Nyssa, in Asia Minor, which in Greek mythology is where Zeus sent his son Dionysus to be raised by the water nymphs who lived there. The species name, sylvatica, means of the trees, from the Latin sylva meaning forest. .
In the past, black-gum has been used to make hatters’ blocks and pistol grips. Today, it may be used in the production of furniture, crates, and boxes.
Black-gum’s oily fruits are a source of food for many species of wildlife, including foxes, robins, ducks, wild turkeys, and European starlings. However, the fruits are too sour for human consumption. White-tailed deer and beavers eat the twigs and leaves. The flowers attract bees and other insects. When large enough, cavities may develop in its trunk that are used by wildlife for shelter.
Cherry tree peeling
Thanks for the pictures. You don’t mention if the tree seems to be growing poorly only that it has a dead branch. We had severely cold winters in 2014 and 2015 which damaged many trees especially those in poor health. Your problems may be related to these winter of have other causes. The presence of the white mold makes me think there is a wood rotting fungi inside the tree and it will slowly die.
The gummois (ooze on the tree) is a response by the tree to an injury much like running a fever when you are sick. The injury could be by an insect (Lesser peach tree borer or American plum borer both attach cherry trees) or a disease such as bacterial canker. These are all serious problems.
My guess it is bacterial canker and you should compare the pictures in the link with you tree.
The big wound on the south side of the tree is called Southwest injury and results when very cold weather and sunny skies in the winter cause the bark to warm up and cool down during the day and get very cold at night. This can kill the bark. The bark splits and the wood of the interior is exposed. You can see from your picture that the bark on either side of the wound is growing to cover the wound and that is a good sign. The peeling bark in your middle photo looks normal and caused by growth of the trunk below.
The white rot in the last photo is a wood rooting fungi that has gotten into the wood of the tree and is now spreading inside the tree and producing the fruit bodies (mushrooms) on the exterior of the tree. I see this fungus on many trees not just cherries it is called White bracket fungi (Irpex lacteus) This fungus is living on the wood and dead tissues of the tree.The trunk will become brittle and easily broken as the wood inside the tree is weakened. I see from your picture that fungus is in the trunk of the tree not just the dead branch. I attach a picture of a dead tart cherry tree with extensive White Bracket fungus.
I would suggest painting the wounds and exposed wood with INTERIOR latex paint.
Blight Killing Branches on Flowering Cherry Trees
By Gene Sumi
Flowering cherry trees at their best – no disease.
Flowering cherry trees, especially the late-blooming Kwanzan variety, have been hit with widespread dieback of branches and stems on their flowering cherry trees. The branch tips die back, leaving clusters of dead, brown leaves. The cause is a fungal disease called Brown Rot Blossom Blight. The blight attacks fruit trees such as fruiting and flowering apricots, cherries, nectarines, peaches and plums.
Fungus spores infect the tree blossoms in the spring, when the blooms begin to age. Many tiny black spores begin to cover the dying flowers. The spores become active and start to kill the branch tip and work back towards the trunk.
Once the dieback begins, the disease cannot be controlled. The only recourse is to prune off the dead portions of the branches and dispose of them in the trash. However, you can help prevent the reinfection of your plants by cleaning up all ground litter from the tree – it may still be harboring the blight spores. The tree should then be sprayed in early spring with a fungicide recommended for control of that fungus. They should be applied when the flower buds swell and begin to show petal color. The tree should be sprayed again after all the petals fall. The applications are done to kill any spores that may be present on the tree.
For the prevention of Brown Rot Blossom Blight, these are the recommended fungicides to be applied to fruit trees in early spring:
- Infuse, by Bonide. Active ingredient: Propiconazole
- 3-in-1 Insect, Disease & Mite Control by Bayer Advanced. Active ingredient: Tebuconazole.
- Serenade, by Agra Quest. Active ingredient: QST 713 strain of Bacteria subtilis.
- Sulfur Plant Fungicide by Bonide.
Sources: Oregon State and Scott Aker, horticulturist at the U.S. National Arboretum.
Cankers on cherry trees may be black knot fungus
If you have cherry or plum trees, now’s a good time to check for a disease called black knot fungus. The fungus can go unnoticed with summer foliage but is apparent when trees are winter-bare.
Also known as cherry knot fungus, the disease causes black tumor-like growths to form along branches. It attacks trees in the prunus family, namely cherry and plum trees. Pin cherry, amur chokecherry, ‘Princess Kay’ Canada plum and American plums are particularly vulnerable, experts say
“This disease is common in Minnesota; it’s everywhere in the state,” said Gary Johnson, University of Minnesota extension professor of urban and community forestry. “It’s not like Dutch elm disease that swoops in and kills. It’s a very, very slow death. Trees can actually live for a long time with the disease. Most of the time people cut the tree down before it dies because it looks so bad.”
“The callous tissue is loaded with spores,” said Bob Olen, horticulturist for the Minnesota Extension Service in St. Louis County. By the time the cankerous growth is noticeable, the disease is within the tree’s vascular system, cutting the flow of moisture and nutrients to the leaves, he said.
The fungus spores — which occur naturally in nature and become airborne — get inside the tree through any wound or opening, such as a break in the bark. Once inside, it moves through the trunk and branches, though the tree’s fruit isn’t initially affected.
“It spreads from plant to plant from pruners, insects, birds, anything that can carry the spores,” Johnson said. “About the only thing you can do is prune.”
If the fungus has girdled the trunk — more likely to happen with young trees without protective bark — there’s really nothing you can do, both Johnson and Olen said. If only branches are affected, regular pruning of the infected branches can control the disease, they said.
The most common mistake is not pruning enough, Johnson said. Because the disease is internal, branches need to be pruned at least a foot down from the coal-like growths.
Pruning away the black knots during winter before more spores are produced and released in spring is recommended. The removed branches should be burned or buried off site.
Care should be taken so the disease isn’t inadvertently spread during pruning. Johnson suggested sterilizing pruning tools between cuts by dipping them in rubbing alcohol and carefully igniting a flame using a cigarette lighter. The flame will kill the spores.
When more than half of a tree’s branches are infected, the tree probably is a lost cause, Olen said, because so little will remain of the tree after it’s pruned back to the leader branches. Once the disease is pervasive in a landscape, it’s difficult to eradicate, even with the removal of the diseased branches, he said.
“The real answer is to move to other species in the landscape if you can,” he said.
Johnson doesn’t recommend using chemicals to control the disease. But according to the South Dakota State University Extension Service, thiophanate-methyl fungicidal spray can be effective in preventing the disease on knot-free trees when applied several times just before buds open in the spring.
Starting with healthy nursery trees and resistant varieties also can prevent problems. They include Asian plum varieties which are more resistant than American varieties, according to the South Dakota extension service.
CANDACE RENALLS covers home, garden and food topics. She’s at (218) 723-5329 or e-mail: [email protected]