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Oak Wilt


Ranger Steve Mueller

Ranger Steve Mueller

By Ranger Steve Mueller

 

Oak wilt can impact your home cooling when shade trees die by exposing the house to heat from the summer sun. The beauty of the yard, as well as a multitude of valuable wild neighbors surrounding your family, will disappear with an oak’s death. Prevention of oak wilt disease infection is important.

The spread of the disease can be most prevalent where new home construction occurs. Once the disease becomes established it is expensive to treat in both money and environment altering impacts.

Oak wilt is a fungal infection that clogs sapwood under the bark of oak trees. Trees ship water and nutrients upward through straw-like tubes called xylem. When the tubes become clogged and flow is stopped, the tree cannot survive. An infected tree can die within weeks. Think about it like very rapid coronary occlusion where blood can no longer supply your heart. The heart will cease to function and your entire body dies.

When water and nutrients are no longer transported throughout the tree, the leaves wilt, growing stems die, and the entire tree succumbs. Some oak species are more susceptible. The red oak group is at highest risk. The white oak group roots do not graft as extensively as red oaks and they have little plugs in their sapwood that slow the spread of fungus growth.

Grafting is common where roots overlap. You might be familiar with fruit tree grafting where a favorite apple variety can be grown on another apple tree by taking a cutting from a favored variety twig, remove a similar sized piece on another apple tree, insert the favored twig, and seal around the surgical implant. That might be an oversimplification but it is the basic process.

Where small oak roots come in contact, the thin outer bark between two roots wears and the inner tissues become interconnected. Once connected bark healing encases them together and material can flow from tree to tree. They are not Siamese twins but physiologically they are attached in a similar manner. They can be separated and it might be essential to stop the spread of oak wilt from progressing through an entire forest.

Forest treatment is expensive so prevention is the most important practice. Treatment is not detailed here.

From April Fool’s Day to the 4th of July is when it is important to prevent oak trees from experiencing open sores. Do not prune branches on oak species or cut down trees during that time. Notice oaks are specified. The fungus Ceratocystis fagacearum is the culprit killing agent. It is oak specific and can spread by two methods. One is from tree to tree through the root grafts referred to as “underground spread.”

The other is by “overland spread”. When tree bark is wounded by cutting branches, it allows sap to flow out and attracts tiny sap-feeding Nitudulid beetles that come to feast on the sweet-smelling sap. Infected trees have fungus blisters that produce spores that get on the bodies of the beetles. When the insect travels to a freshly wounded tree, the fungus is transferred and begins growth.

The adult beetles are active from early spring to the 4th of July. Completing tree and branch cutting by March and not resuming until July is important to prevent the spread of the disease.

During my forestry training I learned painting wounds with pruning sealer tree paint was not particularly important and was an unnecessary expense. Not all foresters agreed. Today applying it has become important to prevent beetle access to save oaks and should be used immediately when a tree is cut down or branches are cut.

Little things like where you place bird feeders is important. Chickadees and titmice take seeds to branches in their nature niche to peck sunflower seed hulls. In the process, they create small openings in branch bark that exposes sapwood to infection. Place feeders on other tree species or use shepherd hooks away from oaks.

Natural history questions or topic suggestions can be directed to Ranger Steve (Mueller) at odybrook@chartermi.net – Ody Brook Nature Sanctuary, 13010 Northland Dr. Cedar Springs, MI 49319 or call 616-696-1753.

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DNR advises earlier caution against oak wilt disease


Avoid unnecessary tree pruning, cutting 

Due to the unseasonably warmer temperatures this spring, the window for the transmission of oak wilt from diseased to healthy red oak trees has already started, the Department of Natural Resources announced today.

According to Dr. Robert Heyd, Forest Pest Management program manager for the DNR’s Forest Resources Division, oak wilt is a serious disease of oak trees – mainly red oaks, including northern red oak, black oak and pin oak – in Michigan and seven other neighboring Midwestern states. Red oaks will die within a few weeks after becoming infected, though white oaks are more resistant and the disease progresses more slowly. This year the disease risk for trees is especially high and ahead of schedule.

“The normal time-tested advice is to prevent oak wilt by not pruning or otherwise ‘injuring’ oaks from April 15 to July 15,” said Dr. Heyd. He said the spread of oak wilt occurs during this time of year as beetles move spores from fungal fruiting structures on last year’s oak wilt-killed trees to wounds on healthy oaks. Because of the warmer weather, the beetles that move oak wilt – and the oak wilt inoculum – are present in many areas.

 “Anyone who has lost trees to oak wilt knows not to cut trees from mid-April to mid-June,” Dr. Heyd explained. “But, with the warmer weather and the higher risk, the time frame has moved up much earlier. Prevention efforts – not cutting and pruning – really need to start now.”

Dr. Heyd said although oak wilt hasn’t been detected in every Michigan county, the need for vigilance is present statewide. “With the transport of firewood and other tree-related activities, you have to assume the risk is present, whether you live in metro Detroit or Menominee.”

Oak wilt has already been detected in the following counties: Alcona, Allegan, Alpena, Antrim, Barry, Benzie, Berrien, Calhoun, Cass, Cheboygan, Clinton, Crawford, Dickinson, Genesee, Gladwin, Grand Traverse, Iron, Kalamazoo, Kalkaska, Kent, Lenawee, Livingston, Macomb, Manistee, Menominee, Midland, Missaukee, Monroe, Montcalm, Montmorency, Muskegon, Newaygo, Oakland, Ogemaw, Oscoda, Ottawa, Roscommon, Saginaw, Shiawassee, St. Joseph, Van Buren, Washtenaw, Wayne and Wexford.

Springtime is a popular time for people to move firewood to vacation properties and other locations. During this April-to-June period, Dr. Heyd said it’s vital not to move wood from oak wilt-killed trees. These trees are often cut into firewood and moved, sometimes many miles from their original locations. Any wounding of oaks in this new area can result in new oak wilt infections as beetles move spores from the diseased firewood to fresh wounds on otherwise healthy trees.

The DNR recommends that anyone who suspects they have oak wilt-tainted firewood should cover it with a plastic tarp all the way to the ground, leaving no openings. This keeps the beetles away and generates heat inside the tarp, helping to destroy the fungus. Once the bark loosens on the firewood, the disease can no longer be spread.

New oak wilt sites have been traced to spring and early summer wounding from tree-climbing spikes, rights-of-way pruning, nailing signs on trees, and accidental tree-barking. If an oak is wounded during this critical time, the DNR advises residents to cover the wound immediately with either a tree-wound paint or a latex paint to help keep the beetles away.

Once an oak is infected, the fungus moves to neighboring red oaks through root grafts. Oaks within approximately 100 feet of each other – depending on the size of the trees – have connected or grafted root systems. Left untreated, oak wilt will continue to move from tree to tree, progressively killing more red oak over an increasingly larger area. These untreated pockets also serve as a source of inoculum for the overland spread of the disease.

Get more information on the background, symptoms and prevention of oak wilt at  http://michigansaf.org/forestinfo/Health/E2764-OakWilt.pdf.

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