Pruning is an important tree maintenance practice that improves tree structure and health. Typically, most trees are pruned during late winter and early spring before their buds break. However, oaks should be pruned during the dormant season (late November to early March) to prevent the spread of oak wilt, a deadly fungal disease. In fact, midwinter (February) is an ideal time to prune oaks.
Every year, many communities lose their valuable oak trees to oak wilt. This disease obstructs the movement of water in the tree, causing its leaves to wilt and eventually lead to its death. Species in the red oak group, like northern pin oaks, are highly vulnerable to this disease and can die within a month once infected. Species in the white oak group (white, bur, and swamp white) are common in our urban areas and are less susceptible to oak wilt. White oak groups may take months or years to decline. Oak wilt is widespread throughout Brown County and the southern part of the state.
Oak wilt spreads by two means - over land and below ground (through root graft unions). Over land, this disease is widely distributed due to the movement of a sap-feeding beetle that carries the oak wilt fungal spores. The beetles are active during the growing season, are attracted to the sap flowing from fresh wounds on the tree, and transmit the fungal spores into the tree tissue. Any wound to an oak tree during the growing season can pose a huge risk in getting infected with oak wilt disease. Human activities like construction damage, pruning during the growing season and transporting infected logs or firewood enhances the spread of this disease.
The following municipalities in Brown County have developed local ordinances restricting the pruning of oaks during the following time frames:
? Allouez: March 15-November 15
? Ashwaubenon: April 1-July 15
? Bellevue: April 1-November 1
? De Pere: April 1-September 1
? Green Bay: March 15-October 15
? Howard: April 1-July 1
? Suamico: April 15-July 15
Local arborists are active during the winter season, so schedule your oak pruning now and don't wait until the end of March. To find the list of certified arborists in our region visit: www.isa-arbor.com/faca/findArborist.aspx. To learn more about tree pruning, download the Extension publication at hort.uwex.edu or contact your local county Extension office.