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  • Writer's pictureCT Trees

Exotic and Native

Tree Diseases in Connecticut – Exotic and Native

Disease Management Guide for CT Arborists (2015-2016) Prepared by Dr. Sharon M. Douglas (CT Agricultural Experiment Station)


Chestnut Blight Canker

Trees in landscapes, woodlots, and forests are subject to a wide variety of problems that threaten their health and the safety of people and property in their vicinity. Tree health problems can affect the aesthetics of the tree or can pose more serious consequences such as disfigurement, economic loss due to reductions in yield and quality, tree death, and threats to safety.

Diseases have also changed the composition of the forest and landscape. For example, until the early 1900’s, the American chestnut was one of the most dominant and important hardwood tree species in the forests of the eastern United States. It was prized for its commercial value as a source of lumber, pulpwood, poles, tannins, railroad ties, and edible nuts.

With the introduction of the fungus Cryphonectria parasitica, a species that was not native to the U.S., chestnut trees became infected with the chestnut blight fungus and the tree was almost completely eliminated from the forest. Today, sprouts continue to grow from old stumps although they usually succumb to disease.

Diseases can be associated with newly introduced exotic pathogens or can be associated with native pathogens that become more problematic for any variety of reasons, including tree stress, changes in climate, or introduction into new ecosystems.

Arborists, tree wardens and other tree care workers who are in the front line in tree care have shown that they can play an invaluable role in helping to prevent or contain infestations by being aware of these exotic problems, and by reporting possible findings of their occurrence as soon as they are noticed.  The goal of this page is an attempt to assist in this effort by providing links to several of the organisms that have been identified as being of specific concern for Connecticut.

Non-Native Diseases That Threaten Connecticut Trees

Among the most well known exotic, introduced tree diseases are white pine blister rust, chestnut blight, and Dutch elm disease.  Other exotic, introduced diseases that threaten Connecticut trees and have been found in the U.S. but have not yet been detected in the state are Ramorum Blight (aka Sudden Oak Death), oak wilt, bacterial leaf scorch, and plum pox.  The list of new and potentially invasive pathogens continues to grow world-wide, with new diseases being described every year.  For example,  the new fungal disease called Chalara ash dieback is reaching epidemic proportions in the United Kingdom after the first detection in 2012.

Ramorum Blight (Sudden Oak Death)

General Information About Ramorum Blight

Federal Regulations and Host List for Ramorum Blight

Decision/Triage Key for Sampling

Oak Wilt

General Information About Oak Wilt

Recent Detection of Oak Wilt in New York

Bacterial Leaf Scorch

General Information About Bacterial Leaf Scorch

Plum Pox

General Information About Plum Pox

Plum Pox Eradication Program

 Native Diseases That Threaten Connecticut Trees

There is a long list of diseases that pose some level of threat to shade and forest trees in the state.  These are diseases caused by pathogens that aren’t introduced or exotic, but they can still cause problems with serious consequences.  This list changes as new discoveries are made.  Among the list of native tree diseases that plant pathologists consider of importance are the recently identified thousand cankers disease, Phytophthora bleeding cankers,  and several needle cast diseases,including  Swiss and Lophodermium.

Thousand Cankers Disease

General Information About Thousand Cankers Disease



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