Great link.
Like most pathogens the fungi is ever present in the soil.
Trees vitality or vigour is what keeps it at bay. Root cutting allowed an entry if it was there.
However, when all is said and done the basic underlying principal remains, and I quote from your source:-
Quote:
Landscape trees with recent wilt symptoms should not be removed immediately. They may "recover" and perform fairly well with some environmental manipulation.
In general, the most resistant plants are those grown in moderately fertile soil in which the balance of major nutrients is tipped slightly toward high potassium and low nitrogen. Generously watered plants are often invaded less extensively than those under moderate to severe water stress.
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With soil conditioning, root growth, suppression to some degree of competing vegetation and an intelligent blend of the right soluble fertilizer you have a fighting chance.
To know if it is verticillium wilt from that document, pick out an infected looking branch and cut it off looking for the streaking.