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Oak Wilt Disease Creeping Its Way Into The Area


An oak tree in Harbert, MI. infected with the first confirmed case of the Oak Wilt disease west of St. Joseph, MI. was being cut down on Monday, March 6 by C & A Arborist.

The C & A Arborist crews were on-site cutting the tree down and properly shreddeing the wood to prevent the spread of the disease to nearby woods. Arborist Christian Siewert said it was significant because the Oak Wilt disease spreads in areas or epicenters and until this time, it has only been discovered north of the Harbor Country area.

This is the first identified case within Harbor Country. The spread is caused by beetles who attack a tree with an open cut, perhaps after a tree is trimmed during the wrong time of the year or if a tree is cut down and infected wood is not properly disposed of. If infected wood is stored, rather than destroyed by chipping, the beetles can infect the stored stored wood or firewood and spread the disease to standing healthy trees. The beetles attack the sap of the tree and eventually cut off the water and nutrients from reaching the body and limbs of the tree, thus strangling the tree. The leaves of the infected tree will then discolor, wilt and die.

Trees with fresh wounds, or cuts, are visited by beetles who transport spores of the fungus. Open wounds create avenues for the entry and spread of the infection. Damage to trees from construction, pruning, or severe storms may lead to new infection centers. It is advised to avoid injury to oaks during favorable conditions for infection, which occur in between April 15 and July 1 in southwest Michigan. At this time of the year the spore mats are present and the beetles are flying. Preventing injury caused by human activity is especially effective in avoiding the establishment of new infection centers on oak trees.

Oak wilt disease kills healthy red oaks and negatively affects white oaks. Once a red oak becomes infected with the oak wilt fungus, the tree will die, and there is no treatment to save the tree. Once an oak wilt infection is confirmed, however, treatments are available save surrounding oaks and stop the spread of the disease.

All red oaks are at risk and are susceptible to oak wilt. Red oaks are common urban and suburban landscape trees and are native to Southwest Michigan. The loss of these trees can have significant negative impacts.

Oak wilt moves slowly through the root system and can travel overland when new spores are moved by beetles from an infected tree to a freshly pruned or injured tree. Oak wilt can be moved farther distances through relocating firewood. An infected oak will drop its leaves in the summer. The disease spreads, killing nearby oaks from one year to next.

Once Oak Wilt has been established in Berrien County, if not managed, it will continue to spread killing all the red oaks in the area. It has been identified in Warren Dunes State Park and is being tended to by the DNR.

The public can prevent the spread of the disease by NOT pruning oak trees during their growth season, March through September. Never transport firewood, oak wilt is spread by the movement of infected wood.

Properly diagnosising Oak Wilt is essential before costly control efforts are begun. Foresters, arborists, or pathologists experienced with oak wilt can often diagnose the problem in the field using host species, symptoms, and mortality patterns.

Mike Dembrowski cuts down the tree
Mike Dembrowski cuts down the tree

Properly sampling suspect trees and culturing in qualified laboratory may be necessary in some cases. Oak trees with unhealthy symptoms may be suffering from another problem, which an arborist may be able to advise on.

Oak wilt usually occurs in discrete, spreading pockets of mortality, with trees on the margins of the infection center becoming infected over time. Declines may occur in discrete pockets, or over a fairly large area, but do not typically spread outward from an initial infection center. Once the oak wilt fungus becomes established in a stand that includes a high proportion of oak, it will often continue to spread through the grafted root systems of the trees, causing infection in healthy oaks. Siewert stated that the Harbor Country area is heavily populated with native oak trees and forests. A wide spread epidemic of this disease could have a very negative affect on the areas natural habitats. He stated that the Emerald Ash Borer killed all of the ash trees throughout Michigan, but he added, there were fewer Emerald Ash trees than there are native Oaks trees. The potential threat of this disease spreading is a much greater problem than the Emerald Ash Borer, said Siewert.

Once an oak tree becomes infected with oak wilt, there is no known chemical treatment that is capable of “curing” the disease; however, fungicide research is continuing. The development of new oak wilt pockets can be avoided, however, either by preventing the development of spore mats of the fungus on diseased trees or by preventing the transfer of fungal spores by beetles to healthy trees. In practice, this involves removing dead or diseased trees and avoiding injury to healthy trees.

For information or services contact C & A Arborists, Inc. at 19271 South Lakeside Rd in New Buffalo or call 269-756-9172 or 269-586-4258.

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Linda Henderson
Correspondent Linda Henderson, AKA Lois Lane, has been passionate about staying on top of late breaking news, ongoing municipal projects and local social events for the past eighteen years. Prior to joining New Buffalo Times, she was a Realtor in Bucktown and Lincoln Park in Chicago, Il. She says, “Waking up and seeing the beauty of Lake Michigan everyday keeps me going, along with my labradoodle and sidekick, Scruffy.”