How to Detect and Control Beech Bark Disease

    PictureWhat is beech bark disease?

Beech bark disease is a disease of American beech (Fagus grandifolia) that occurs when an exotic scale insect, called beech scale (Cryptococcus fagisuga), colonizes beech
and makes them susceptible to invasion by one or several
species of canker-causing Neonectria fungi.

Native to Europe, beech scale was introduced into Nova Scotia, Canada around 1890. The scale and disease have been moving west and south across the United States and Canada since that time. The disease was first detected in Michigan in 2000. The scales are easily spread by the wind, birds, and as hitchhikers on infested firewood.

Would it kill a tree?

Fungal invasion creates regions of dead wood tissue (cankers)
beneath the bark. This restricts the flow of water and nutrients,
killing the tree over time. Most beech trees are susceptible to beech bark disease and will be killed. Research has shown that only a small percentage (<5%) of American beech is resistant to this disease. When the disease first establishes, about half of the large beech trees typically die. Infected trees are structurally weakened and very susceptible to trunk breakage during high winds.

Where is the beech scale found in WI?

Beech scale was first detected in east of Sturgeon Bay in Door County, Wisconsin in August 2009. Mortality of beech trees was also observed in the areas where scale populations were high. It is affecting Beech trees along Glidden Drive.

What does the beech scale look like?

Scales are tiny insects (0.5 to 1 mm) related to aphids. Like aphids, they have a long tube-like mouthpart called a ‘stylet’ that is inserted into the tree to feed. Adults lay eggs during the summer and the eggs hatch in the fall. Once the young scales find a suitable location on a beech tree, they insert their stylet into the tree and begin feeding. They lose their legs, become covered with a woolly wax, and remain there for the rest of their lives. They overwinter in this stage, and become adults in the spring.

What does the infestation by the beech scale look like?

When a beech tree is heavily infested with beech scale, the entire trunk may appear white. When scale infestation is light, there may only be tiny spots or patches of white wool on a tree trunk or a branch. Infestations often begin on rough surfaces such as rough bark, near old branch stubs, under large branches, wounds, cracks, or beneath mosses or lichens. Since many scales are washed down by rain, infestations are more commonly found on the lower part of a tree. At an early stage of scale infestation in a stand, “white wool” produced by the beech scale may resemble lint or a snowflake. It is common to find heavily infested trees next to lightly infested trees.

How does beech bark disease affect yard trees?

Diseased trees are a safety hazard because they can snap in high winds. In areas where failure of beech may be a hazard to people and structures, a tree may need to be removed once it is moderately infested with the scale.

How can I control attacks from the beech scale?

In Lower Michigan, invasion by the fungi occurs several years after initial infestation by beech scale. Keeping most of the scales off the tree may reduce the risk of infection by the fungus. A tree with only a few scales will produce fewer scale offspring, delaying population buildup. In a recent study conducted in Michigan, use of a variety of insecticides and fungicides was not effective in controlling beech scale or beech bark disease. However, physically scrubbing scales off the trees provided effective control. For high value landscape trees it is recommended that the scale insects be removed by physical scrubbing or by washing off with water using a high pressure sprayer.

                                                                                                     article courtesy of Carolyn Rock, naturalist at
                                                                                                                    Whitefish Dunes State Park