May | June 2010


g r o w i n g Walnut canker a


concern


Healthy black walnut tree.


Black walnut branch infected with Thousand Canker disease.


Missouri has adopted an external quarantine on move- ment of wood from black walnut (Juglans nigra) from 11 Rocky Mountain and Western states in an effort to prevent introduction to the state of Thousand Canker disease, caused by the pathogen Geosmithia morbida sp. nov and the insect that vectors it, Pityophthora jug- landis. The regulation applies to nursery stock, bud- wood, scionwood, green lumber, logs, stumps, roots, branches, and composted and uncomposted chips.


Meanwhile, USDA’s Animal & Plant Health Inspec- tion Service (APHIS) has conducted a preliminary risk assessment that concluded that introduction of Thousand Canker disease into the native range of the black walnut (most of the eastern U.S.) would threat- en a timber resource worth $500 billion.


39


Black Walnut Tree infected with Thousand Canker disease.


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