I had an email forwarded to me from the Minnesota Department of Natural Resources (DNR) about pruning oak trees. You should not prune oak trees in the months of April through July in Minnesota. Well, I guess you could prune your oak trees if you did not mind hiring a Professional Tree Service to remove your dead oak tree!

Oak wilt is a fungus that can affect all species of oak trees. The pathogen invades the water-conducting vessels in the oak tree and eventually kills the tree. Red oak trees are killed in about two months, bur oaks are killed in one to seven years and white oaks are a little tougher and can survive may be up to 20 years before dying. The sad fact is we have the knowledge to stop the spread of oak wilt.

There are two ways oak wilt spreads to uninfected trees. The oak wilt fungus can be spread by sap beetles. If you prune oak trees in the spring and early summer the open wound from pruning is just what the sap beetles need to spread oak wilt. No open wounds on the oak tree and it is much more difficult for the sap beetles to spread the disease.

The other way oak wilt spreads is through root grafts or roots from infected trees that have grown together underground with healthy oak trees. This spread of course would be very slow-moving the fungus underground in the root system from one tree to the next. The sap beetles are much more mobile and I am sure is the major reason oak wilt is spreading in Minnesota.

Oak wilt was first discovered in Minnesota around 1945. It is widespread in southern and southeastern Minnesota and moving northward. If you suspect you have a tree with oak wilt contact your local DNR forestry office or I am sure your local University of Minnesota Extension office could help too. Remember, do not prune oak trees in the months of April Through July!

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