Exotic Pests and Diseases Posing Threats To Northcentral Ohio Forests

The gypsy moth (Lymantria dispar), is a destructive defoliating insect pest that attacks oak forests throughout the northeastern United States. Gypsy moth has been present in Ohio since the early 1970’s and is now well established in the northern half of the state. Since the early 1990’s, gypsy moth has inhabited Mohican-Memorial State Forest (MMSF). Aggressive gypsy moth management strategies have protected most of the oak forests at MMSF. Gypsy moth have caused moderate levels of oak mortality, especially on drier sites and where management was delayed. Wet weather conditions have prevented outbreaks in recent years, but the gypsy moth is still present at MMSF. The risk of future outbreaks is still high if Ohio has normal or dry spring weather.

The hemlock woolly adelgid (HWA) is a small aphid-like insect that has caused eastern hemlock trees to decline and die in the northeast U.S. Hemlock trees are found in the steep, cool ravines and gorges that make Mohican-Memorial State Forest a special place. HWA has not been found infesting natural stands of hemlock trees in our state, however, the insect was discovered in two Ohio landscape plantings in 2002. The infested trees, found in Lake and Summit Counties, originated from out-of-state nurseries. Fortunately, these infestations did not escape the landscape trees and infest surrounding trees. These incidents show how easily HWA can be accidentally introduced into Ohio from another state.

American beech trees growing at Mohican-Memorial State Forest are potentially threatened by Beech bark disease (BBD).  This disease has been killing American beech trees in the eastern United States since the 1930's.  The disease is actually an interaction between the beech scale (a non-native insect) and Nectria fungi. The fungal pathogen infects bark wounds created by the scale insects.  BBD has killed beech trees in WV, PA, NY, NJ, ME, MI and NC.  The beech scale was first discovered in Ohio in 1985 at the Holden Arboretum in Lake County.  In 2003, Nectria fungus was found infecting beech tree bark at the Holden Arboretum, confirming BBD in Ohio.  It may be only a matter of time before this disease finds its way to MMSF.

Flowering dogwood trees add beauty and valuable wildlife food to Mohican-Memorial State Forest.  Dogwood anthracnose is a fungal blight affecting the leaves and twigs of flowering dogwood trees.  The disease weakens the trees and causes twig dieback.  Significant tree mortality has been linked to dogwood anthracnose, particularly at higher elevations in West Virginia and North Carolina.  Flowering dogwood trees at MMSF have been impacted and killed especially on the cooler, moister sites.  Fortunately, trees on warmer, drier sites with good air movement are less impacted.  So, while dogwoods are not doomed, this disease is an important factor to consider at MMSF.  Dogwoods on the edges of openings and other areas with more light and air movement can continue to flourish at Mohican.

The emerald ash borer (EAB) is a non-native insect pest of Asian origin that was discovered near Detroit, Michigan in May, 2002.  Positive identification of the insect followed in July, 2002.  EAB was also discovered in Ontario, Canada during the same summer.  EAB has subsequently been found in Northwestern Ohio, Central Ohio, northeastern Indiana, Virginia, and Maryland.  The larvae of this beetle develop in the living tissue beneath the bark of ash trees. Their feeding on these tissues causes decline and death of the host tree within 2-3 years.  This is a serious pest that could have tremendous impact on ash trees growing in Mohican-Memorial State Forest.

The sudden oak death (SOD) fungus has killed tens of thousands of oaks and tanoaks in California. The fungus causes only leaf spots and twig dieback on other hosts, many of which are commonly used in the nursery trade. SOD infected trees are also found in Europe.  Northern red oak have been infected and killed in the Netherlands and southern red oak have been similarly affected in England.   Pin oak, mountain laurel, sourwood, and witch-hazel have also exhibited susceptibility to the SOD fungus.  While the fungus causing this disease has not been found in Ohio, red oaks and other trees and shrubs at MMSF are certainly at risk if this disease becomes established here.