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Tree Diseases

Tree Cold Sores: The Seiridium Canker

By: Lacey Russell, PhD | July 23rd, 2018

Seiridium, one of many tree diseases, is a cankerous, fungal disease that is found all over the country, just blowing in the wind. Seiridium canker is a major problem on cypress (Arizona, Italian, Leyland) and and Thuja species (also called arborvitae). It can also be a minor problem on junipers.

The fungus tend to infect trees that are stressed due to low rainfall. The trees may crack and “fork” due to the drought, leaving an opportunity for the disease to enter the tree.

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Seiridium canker is the asexual (anamorph) state of a fungus called Lepteutypa cupressi. Aggressive strains of the disease may kill small trees in less than a year while larger or weaker strains may take several years. Trees that are already under stress from environmental problems such as drought, poor soil, etc. may show more severe symptoms from the seiridium infection.

Japanese cedar (Cryptomeria japonica), and Sierra juniper (Juniperus occidentalis), and the variety of arborvitae called ‘Emerald Green Giant’ are reported to be resistant to the disease.

So, what's a canker?

A canker is an area on your tree or shrub where a bacterial or fungal infection has begun. The cankers become larger as the fungi or bacteria infect healthy tissue. Since the cambium in a canker is dead, no new xylem or phloem is formed, thus weakening the tree.

The tree continues growing, despite the canker, to produce healthy wood and bark around the infected area. This creates a sunken area at the canker site. If a canker covers enough of the circumference of a trunk, the tree becomes severely weakened.

Flagging Branches

If your tree is infected with seiridium, you may notice some branches that are turning brown and flagging (drooping brown). You will be able to distinguish these symptoms from those of drought or natural dieback because usually only one or two limbs will show the symptoms at first.

Oozing Cankers

If you follow the brown branches to the trunk you may notice a resinous oozing canker. This oozing resembles sap flow. The cankers aren’t usually near the shoot tips, but are located several feet down the branch close to the trunk.

The cankers can also occur on trees that do not yet show the flagging symptom. Although the limb is infected, the canker has not yet girdled the entire branch and it remains green. It is likely that these branches will discolor in a few weeks.

Keep in mind that although resin production and oozing is common with seiridium infections, old or slow growing trees may not have oozing cankers. If you scratch the surface of the cankered area, the woody tissue underneath is often gray or brown.

The Seiridium Life Cycle

Seiridium is a fungus and survives during cold or dry weather in infected bark tissue. During wet weather, the spores are released and spread to nearby hosts or uninfected branches. The spores are spread by splashing and water runoff, and can also be carried by contaminated pruning tools and infected plants that are moved from place to place. They may lodge in cracks and crevices in the tree or be transferred by insects.

Black, pustule-like fruiting bodies known as pycnidia may appear breaking through the bark when viewed under a hand lens. During rainy weather, these fruiting bodies release spores that are spread by splashing water, carrying infections to wounded twigs or stressed trees. If the infections spread to multiple branches or on the main trunk, the tree may die. This disease may kill large portions of the tree in spring and summer.

How to Control Seiridium

According to a study done in 2011, some fungicides such as thiophanate methyl and boscalid have been shown to decrease the growth and spread of the disease. Contact a tree health specialist to help you control the disease with a fungicide.

Keep Trees Happy

Seiridium canker tends to infect trees that are weakened by environmental stress.

Water your trees during periods of low to no rainfall (drought) and fertilize based on soil test recommendations.

Reduce the Spread of the Disease

Prune and throw away or burn infected limbs. Prune the limb 3 to 4 inches below the infected canker and don’t compost them or leave them lying around.

Fungal spores are so small and light that just a light rain can send them soaring into the air to find a new host. Put them in a trash bag then in a covered garbage can. Burning them is also a good way to kill the disease and get rid of the infected limb.

Be sure to practice sanitation pruning methods. The spores from the infected tree can easily transfer onto your tools only to infect a healthy tree or limb.

Seiridium canker spores love to land on wet leaves, especially those growing in a shady area. If you use overhead watering systems, try to water in the morning so the leaves have time to dry out during the day.

Sanitation Pruning Methods

There are a few ways you can clean your tools after working with an infected branch. You can spray them with a disinfectant such as Lysol or dip them in a 70% alcohol solution or a 10% bleach solution. Bleach can be very corrosive to metal, so alcohol is the preferred way to sanitize between branches. You will want to let it soak in the alcohol for a minute to be sure they are free from fungal spores.

Choose Resistant Plants & Trees

In the unfortunate situation where a tree dies from a Seiridium infection, it is best to remove and dispose of the tree. Replace it with something that is more resistant to the disease such as ‘Emerald green arborvitae’ or ‘Crytomeria japonica.’

Keep an Eye Out

Early detection and prevention are the best ways to manage this fungal disease. Walk around your landscape regularly to see if you spot any flagging branches on your cypress and or arborvitae trees.

Avoid overhead watering, fertilize according to soil test results, and be sure to water your trees during times of drought. Consult with a tree health specialist for advice on how to manage your landscape so that your plants are thriving and beautiful.

And, as always, don't just look out for your own trees but keep an eye on your neighbors trees as well. The best way to keep your trees from infection is to keep tree diseases from spreading through your neighborhood.

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