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Monday - March 26, 2012

From: Austin, TX
Region: Southwest
Topic: Diseases and Disorders, Trees
Title: Hypoxylon Canker removal in Austin TX
Answered by: Brigid & Larry Larson


I have several oaks that appear to have been killed by Hypoxylon atropunctatum from last summer's drought. Is it safe to cut them down in March or does that risk spreading Oak Wilt too. Should I let them sit there dead until summer?


Mr Smarty Plants offers his condolences on the loss of your Oaks.  That always hurts. 

Your question evoked considerable discussion amongst the experts at the Ladybird Johnson Willdflower Center.  It's clear the trees need to be removed, but there were good arguments for either "right now" or "wait until next winter". A general concensus clearly recommended that you employ the services of a Texas Oak Wilt Certified Arborist and get a expert diagnosis of the trees condition and recommendation for how to go on.

The argument for waiting is the one you implied. When considering Oak Wilt, it’s just a bit late to be cutting trees down.  The standing advice is to prune from December into early February. The risk you induce by waiting is that the Hypoxylon Canker that is there may infect other trees.  You can have hope that this year this risk is minimal as the references linked below imply that healthy, well watered trees are not all that susceptable to the canker. There is also a risk, in truly advanced cases, that the tree wood will be weaked by the fungus and drop limbs or fall.  

The argument for "cutting now" is that you do have Hypoxylon Canker there.  Leaving the trees stand until summer or later is leaving a viable source of the fungal infection in place. The Florida Forest Service describes the fungal growth process.  In the spring or early summer, masses of spores called conidia are produced on the surface.  Later in the summer or fall, after the powdery conidia are gone, the fungal stromata thicken and produce another type of spores. These are the infective ascospores which are present later in the summer or fall.    The Florida Forest Service recommends removal of the tree. 

 The Oklahoma State Extension recommended “In a home setting, individual trees that have more than 15% of the crown area infected should be cut to ground level and burned. No stump should be left because stroma development has been observed even on very small stumps.” The Texas Forest Service also has a publication describing the course of the infection, and there are  several publications from TAMU including a 3-part fact-sheet. This one addresses managing Hypoxylon canker.

It makes sense to remove trees that can serve as viable sources of continuing infection, but at the same time one should be concerned about Oak Wilt as that is a continuing concern for the other trees.  One should take extreme care that the neighboring Oak trees are not damaged by the removal and follow the expected precautions following the work. This includes tool cleaning, not storing infected wood on the property, and all pruning cuts or other wounds, including freshly-cut stumps and damaged surface roots, should be treated immediately with a wound or latex paint to prevent exposure to contaminated insect vectors. I will repeat the recommendation of consulting a certified Oak Wilt Arborist!

Mr Smarty Plants has produced several answers concerning Hypoxylon Canker, most of them involve determining that this is the source of illness.  There are several other good links in these answers though. 


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