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Annosus Root Rot: A Closer Look

Everything You Need To Know About ARR

Trees are like members of our family who we make stand outside all day. Which is fine for the most part, because, well, they’re covered in bark and that means they’re less at risk of damage and infections. But, when it comes to problems like Annosus Root Rot, we begin to see just how much damage an acute fungal illness can do.

Join us, today, as we discuss “the most economically important forest pathogen in the Northern Hemisphere”.

Annosus Root Rot

Annosus Root Rot

A Definition Of Annosus Root Rot

Also known as heterobasidion annosum, ARR is a fungus that infects trees throughout the United States.

And the results are devastating, across the board. Considered one of the most destructive conifer diseases, ARR is responsible for the deaths of more than a billion U.S. dollars’ worth of trees, per year.

The disease primarily infects Southern Pines (such as loblolly, slash and shortleaf), and Eastern White Pine. It’s a summertime problem, for the most part, with basidiospores taking to the air and infecting trees which are susceptible to the disease.  

And which trees are more likely to fall prey to this condition? As it turns out, trees with damage done to the bark in the form of cuts or abrasions, leaving their soft underbellies exposed to the elements. Whatever the wound, once the airborne spores make their way to the tree, they enter and begin to grow through the heartwood and into the roots.

The end result? These cause decay in the root system, spreading throughout the tree’s roots, and leaving it much weaker. Diseased trees may be more likely to succumb to windthrow or broken branches and limbs.

In human pathology, when a deadly disease becomes airborne, we panic, because we all breathe and eat, and many of us walk around with open wounds. We’re aware of how susceptible we are to it, and this works similarly for trees. Annosus Root Rot is a deadly condition, and it doesn’t take much for it to spread.

How To Identify It

Like with many other spore-based diseases, one of the easiest signs for recognizing ARR is growths. Look for fruiting bodies or basidiocarps. These look like long, flat, bubbly mushroom caps, stretching around the body of the tree like an umbrella. These are white around the edges and dark brown in the middle.

As the disease progresses through its various stages, the bark changes color from pale yellow to a light brown. In its final stage, it turns white with a light streak of black spots.

How To Manage It

Any treatment of annosus root rot should start with isolation.

Using water agar with infected host tissue, you can produce conidiophores to eliminate the disease.

You can also isolate the disease with living sapwood from Picea abies, cutting out thin disks from the wood and laying them in Petri dishes. This is done in order to culture bacteria which, in turn, are placed on moist filter paper. While it may seem simple, this is a technique that allows spores to be captured from the air before they can do any damage. The asexual stage of the fungus actually forms on the disks during this time, rendering it harmless to your trees.

The three ways of managing this disease include:

  • silvicultural control measures, in which we plant species of trees which are less susceptible to infections


  • chemical methods, including prophylactic stump treatment with a solution of urea. This should be done immediately following the initial infection
  • biological control, in which another fungus with a neutralizing effect is applied to the infected area. The top contender for this treatment is known as Phlebiopsis gigantea.


Don’t Let ARR Get The Best Of You

Annosus root rot is a devastating tree disease and, left unchecked, can cause thousands of dollars in tree damages. But the active word there is “unchecked”. There are many steps you can take to help curb the negative impacts of ARR on your trees. You just need to take action without waiting too long.

Interested in learning more about this and other tree diseases, or just some basic yard maintenance and our tree removal services? Get in touch with us, today, and unearth the world in your backyard.

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