Saturday 25 April 2015

What’s Affecting Your Trees?

Posted at 5:25 PM

Dutch Elm Disease

Affecting elm trees across Wisconsin, Dutch Elm Disease (DED) is one of the most destructive shade tree diseases in North America. Born of a fungus, and often spread by elm bark beetles, DED infects the water conducting system of elm trees, resulting in decreased or clogged water movement to the crown. The dehydration causes visual symptoms, as the infected tree begins to wilt and turn yellow or brown in color.

If the fungus enters the tree through the roots, symptoms may appear in the lower crown first and then continue to spread to the entire crown very rapidly. If the infection begins higher in the crown, symptoms often appear on individual branches, possibly in several locations, and progress downward. Symptoms are typically seen early in the summer (think 4th of July), but may also be exhibited any time during the growing season.

Luckily, DED is a manageable disease. The most effective treatment is to remove diseased trees or branches in areas with large elm populations to reduce breeding sites for elm bark beetles and to eliminate the source of the fungus. Fungicides have proved to show significant results in preventing the infection. Through a process known as macro-infusion, the fungicide is injected directly into the root flares of the tree, killing the fungus and preventing future infiltration. If you suspect that your tree has Dutch Elm Disease, contact your tree care professional right away to explore your treatment options.

Oak Wilt

Oak Wilt is another fungus that has significantly affected trees across the state. This fungus also invades the water supply system inside the tree, creating balloon-like bumps that plug water movement up the tree.

Oak Wilt can be spread both below and above ground. The fungus can spread when roots from diseased trees become intertwined with roots from a healthy tree. This generally occurs between oaks of the same species and is more common among red oaks. The disease can also be spread by sap-feeding beetles. Fungal mats caused by the disease develop under the bark of some trees and can force the bark to crack open. The fungus produces a sweet odor that attracts these beetles, which then fly to healthy oaks, carrying the fungus with them.

Oak Wilt can be very difficult to detect. Leaves on diseased oaks often develop yellow veins that eventually turn brown. Infected trees also lose their foliage much sooner than healthy oaks and may have visible narrow cracks in the bark leading to hollow areas between the bark and the wood that give off a distinctive odor similar to fermenting fruit.

The best treatment for oak wilt is to avoid it in the first place. To prevent the spread of Oak Wilt, avoid pruning, cutting or wounding oak trees from April until October or whenever temperatures are above 50 degrees. An often used control measure for oak trees that are located close to one another is the construction of a root graft barrier which disconnects any shared root systems between the trees. Finally, in areas where oak wilt is prevalent, trees may be effectively treated with a systemic fungicide injection to prevent the infection.

Once infected, oak trees in the red oak family (those with pointed lobed leaves) cannot be saved. The white oak family of trees (those with rounded lobed leaves) may be cured of the disease if it is detected and treated early. To have your oak trees examined for Oak Wilt and to discuss treatment options, please contact the disease control experts at First Choice Tree Care.