If you notice the sudden death of large branches or sections  in your Sugar Maple or Norway maple , there's  a good chance that its either Nectria Canker or Verticillium Wilt.   

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These diseases affect many tree species but for the homeowner you are most likely to see it in your Maple trees.

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Both diseases are caused by a fungus that attack the living bark within the infected branches and choke off the lifeline of water and nutrients to the terminal leaves.  Nectria Canker invades from open wounds on the branch while Verticillium wilt moves  up from the soil.  Both diseases can spread from  the trunk - and from the trunk - up and down the tree.  Verticillium wilt tends to be more common in sugar maple and often can kill the tree.  Nectria Canker is more common in Norway Maple and may not kill the tree but cause significant dieback.

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If an infected tree survives the first year of infection, the tree can often isolate the fungus through a process called compartmentalization - basically the tree isolates the fungus to the area that it has already infected and keeps it from spreading the following year.  It doesn't always work but when it does , there is a chance for recovery.

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Pruning branch  areas infected with  Verticillium wilt will only marginally assist the tree as the disease is established within the trunk (coming from the roots) .  Pruning for Nectria Canker can lower the reserve of the fungus in the tree and offer some benefit.  

 The dead give away that these funguses have attacked your tree is the sudden rapid death of the branch -usually resulting in the leaves  going brown and staying on the branch;  and also  the dark staining of the living wood on the infected branch.  Nectria Canker will produce  spores that look like orange pimples on the wood late in summer or fall.  Veticillium wilt, as it is a soil borne disease does not produce a visible spore body.  

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