Hypoxylon Canker

By far, the most prevalent tree disease I encounter is Hypoxylon canker. It affects nearly every species of tree native in our area. The disease typically targets stressed trees during drought conditions, so you can imagine how central Texas is a great niche for this sapwood fungal disease.

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Hypoxylon is a native disease, unlike oak wilt which is believed to be introduced. I like to compare hypoxylon to the flu. It is out there, everywhere, all the time. You just need the right stresses and stars to align to come down with it and get sick. Hypoxylon works the same way. The spores are out there, all over the place. They are in the cracks in tree bark, in the soil, blowing in the air, everywhere. The main difference in my analogy here is that if you get the flu, you’ll probably just feel bad for some number of days. However, if your tree gets hypoxylon, it is highly likely going to die. “Is this tree going to make all my other trees get sick?” I get asked that questions regularly on sites where hypoxylon has been identified. This is a complicated question to answer. I’ll go back to my flu analogy. If you walk into a room where someone has the flu, are you going to get sick? Hard to say, isn’t it. If you are currently sleep deprived, been working hard outside and give the person a kiss, then, yes, you will probably get sick. If you are well rested, well nourished and keep some distance, then, maybe you’ll get by ok. Going back to trees, if a tree gets hypoxylon, it doesn’t mean every tree around it is going to get sick, but the chances go up. We call this disease pressure.

Prevention is the best medicine. We know this disease prays on drought stressed trees during extreme heat conditions. Watering your tree(s) is by far the best practice to help reduce the chances of getting hypoxylon. Beyond that, anything that helps improve the overall health of the tree and improves water retention in the soil is going to help. Good fertilization practices can help, pruning out diseased limbs can help, composting and mulching the soil can help. If you find this disease attacking a tree on your property, I highly recommend you look at developing a comprehensive plan for improving the growing conditions on your property.

There is no fungicide or other “treatment” out there to spray or inject into the tree to stop the disease progression. I’ve tried everything under the sun.

I’ve read and discussed with respected colleagues about a notion that there is some correlation between oak wilt and hypoxylon. Some people believe that hypoxylon can be: instigated by oak wilt infected trees, weaken trees to become prone to oak wilt infection or otherwise tied together somehow. I don’t buy any of these theories. For a long time, many “arborists” tried to diagnose just about all dying oaks as oak wilt. With that, all kinds of theories were conjured up. My eyes tell me that hypoxylon is totally capable of killing trees outside of any interaction with oak wilt. I have never seen a site where clues existed to indicated a tree caught oak wilt due to a hypoxylon infection.

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