Nectria Canker Treatment – What Causes Nectria Canker
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By: Mary Ellen Ellis
Nectria canker on trees is a fungal infection. The pathogen known as nectria invades fresh wounds and damaged areas of bark and wood. If a tree is healthy, it can typically seal off the infection and recover with a callus formed. Weaker trees may get girdled and ultimately die. Know the signs of nectria canker, how to prevent it and what to do if you see it.
What is Nectria Canker?
What causes nectria canker disease is one of the several nectria fungal species. These fungi are opportunistic and attack trees at their weak spots from injury, pruning, root damage, freezing, pest infestations, and other diseases. Any damaged wood is susceptible to this pathogen and the resulting disease.
Signs of Nectria Canker
The characteristic sign of nectria canker is the formation of the cankers, wounds on twigs, stems, and trunks that look like sunken areas that may be discolored. The cankers may not be discovered until other signs of disease develop. These include girdled twigs and branches, dead branches that don’t produce leaves in the spring, and wilting on branches.
You may also see the fruiting bodies of nectria. They typically appear in the spring and summer months and are orange or red spheres that are very small. Eventually, they turn a lighter color and grow white spores on the surface.
Nectria Canker Treatment
Nectria rarely kills older, established trees. Most are able to fend off the fungus and form the characteristic calluses. Older trees that are not healthy may be vulnerable, but it is typically younger trees, especially those that are newly transplanted, that can be killed by nectria canker.
There is no cure for nectria canker, so it is important to take steps to prevent it affecting young and vulnerable trees. Pruning injuries can be a major source of infection, so avoid pruning trees in the fall, especially in wet conditions. Restrict pruning to dry weather and remove any branches or stems that have been infected with the fungus.
Freezing damage is another important way in which trees get infected. For young transplants, providing protection from freezing can prevent the disease. Avoid other types of injury and keep your trees healthy to minimize the risks from nectria infection. This means being careful with the lawnmower around trees, preventing or managing pests, and providing adequate water and nutrients.
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Locate the cankers on the branches of the apple trees. European canker fungus manifests itself as reddish brown lesions below leaf scars on smaller branches and lengthen to form ridged cankers. Nectria canker fungus produces puffy, cream- or pink-colored bumps, called sporodochia, that turn cankerous as the season progresses. Cankers originating from anthracnose and perennial canker bacteria resemble European cankers so closely that you can’t distinguish between them.
Mix together 9 parts water to 1 part chlorine bleach in a plastic container. Place the container next to the canker-infected apple trees.
Prune any diseased or damaged wood back to the first sign of healthy tissue with pruning shears or lopping shears. Make the pruning cuts at 45-degree upward angles to help prevent moisture from coming in contact with the exposed tissue. Sanitize the blades of the pruning or lopping shears after each cut by dipping them in the bleach solution.
Collect the infected wood and burn it. Fungal spores can still infect other plant life in the vicinity after removal through wind transfer.
Canker Diseases - Hardwoods
Cankers caused by Neonectria:
Cankers caused by Neonectria ditissima. Old name for the same fungus is Neonectria galligena (and an older name is Nectria galligena)
Neonectria ditissima on birch
A classic taget-shaped Neonectria canker on sassafras. Note old branch stub in the center where the canker started. The fungus entered a wound on this small branch and moved down the branch and into the main stem.
Cankers on branches produce sporodochia soon after infection. Here a small branch was killed by the fungus and sporodochia (black when dry but can be reddish colored when fresh) formed producing asexual spores.
Neonectria canker with perithecia (small reddish structures - a little hard to see) formed on some of the bark adhering to the canker face.
Red perithecia of Neonectria foemed on the edge of a canker. The perithecia produce ascospores that cause new infections.
Nectria Cankers on Honey Locust:
Nectria cinnabarina on a thornless and seedless cultivar of honey locust.
Sporodochia producing asexual sores are produced on the cankers.
Nectria cinnabarina sporodochium. This cushon-shaped asexual fruiting body swells when wet and produces asexual spores.
Perithecia of Nectria cinnabarina clustered on old sporodochia.
The wild type honey locust has large thorns and lots of seed pods. Cultivars selected that are thornless and seedless are very susceptible to cankers caused by Nectria cinnabarina. This fungus is usually a saprophyte on woody plants but is a serious pathogen on the thornless and seedless cultivars of honey locust.
Once N. ditissima establishes itself in a host, management should focus on sustaining the vitality of the tree or shrub. Remove and discard cankered branches during the winter when the fungus is dormant. Irrigate when conditions are dry to avoid the development of drought stress, fertilize if soils are deficient in minerals, prune to preserve sound branch structure, avoid wounding the bark and maintain a layer of mulch over as much of the root zone as possible.