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Invasive Species: Diseases

Invasive Diseases

Species that are not native and also have the potential to harm human health or to harm natural, agricultural or silvicultural resources can be listed as prohibited or restricted by the State of Michigan. If a species is prohibited or restricted, it is unlawful to possess, introduce, import, sell or offer that species for sale as a live organism, except under certain circumstances.

Beech Bark Disease

(Cryptococcus fagisuga + Neonectria spp.)

Beech bark disease (BBD) is caused by both a sap-feeding scale insect and a fungus. American beech trees are first infested with beech scale. Scale feeding allows infection by the Neonectria fungus. The fungus kills the wood by blocking the flow of sap. Some infected trees break off in heavy winds before dying. The scales are covered with white wool, turning infested portions of the tree white.

More information: Beech bark disease

Beech Leaf Disease

(Litylenchus crenatae and potential associates)

Watch List

Beech leaf disease is associated with the microscopic worm Litylenchus crenatae, a nematode that enters and spends the winter in leaf buds, causing damage to leaf tissue on American beech and European and Asian beech species. Trees become susceptible to other diseases and can die within six years.   

More information: Beech leaf disease

Boxwood Blight

(Calonectria pseudonaviculata)

Boxwood blight is a serious fungal disease that attacks boxwood, a popular landscape shrub, as well as Japanese spurge, Allegheny spurge and sweet box.  The disease can quickly defoliate boxwood plants on the landscape and in nurseries.  This fungus can spread via the transport of infected plants that may not show any symptoms at the time of shipment and also from infected plant parts such as boxwood foliage in holiday greenery.

More information: Boxwood blight

Oak Wilt

(Bretziella fagacearum)

Oak wilt kills healthy red oaks. White oaks can also be affected but are more resistant and less vulnerable to mortality from the disease. Look for red oaks that suddenly drop their leaves in the summer. The disease spreads, killing nearby oaks from one year to the next.

More information: Oak wilt

Thousand Cankers Disease

(Pityophthorus juglandis + Geosmithia morbida)

Watch List

Thousand Cankers Disease involves an insect native to the southwestern U.S. The disease affects black walnut trees, a valuable economic and ecological resource in Michigan.

More information: Thousand cankers disease