Damaging Agents
The most serious disease of Juglans cinerea is butternut decline or butternut canker. In the past the causal organism of this disease was thought to be a fungus, Melanconis juglandis. Now this fungus has been associated with secondary infections and the primary causal organism of the disease has been identified as another species of fungus, Sirococcus clavigignenti-juglandacearum. The fungus is spread by a wide-ranging vectors, so isolation of a tree offers no protection. Symptoms of the disease include dying branches and stems. Initially, cankers develop on branches in the lower crown. Spores developing on these dying branches are spread by rainwater to tree stems. Stem cankers develop 1 to 3 years after branches die. Tree tops killed by stem-girdling cankers do not re-sprout. Diseased trees usually die within several years. Completely free-standing trees seem better able to withstand the fungus than those growing in dense stands or forest. In some areas, 90% of the butternut trees have been killed. The disease is reported to have eliminated butternut from North and South Carolina. The disease is also reported to be spreading rapidly in Wisconsin. By contrast, black walnut seems to be resistant to the disease.
The hybrid between Butternut and the Japanese Walnut is commonly known as the 'Buartnut' and shows resistance to the Butternut Canker. At Prospect Rock Permaculture, researchers are back-crossing Butternut to Buartnut, creating 'Butter-Buarts' which should have more Butternut traits than Buartnuts. They are selecting for resistance to the Butternut Canker.
Bunch disease also attacks butternut. Currently, the causal agent is thought to be a mycoplasma-like organism. Symptoms include a yellow witches' broom resulting from sprouting and growth of auxiliary buds that would normally remain dormant. Infected branches fail to become dormant in the fall and are killed by frost; highly susceptible trees may eventually be killed. Butternut seems to be more susceptible to this disease than black walnut.
The common grackle has been reported to destroy immature fruit and may be considered a butternut pest when populations are high.
Butternut is very susceptible to fire damage, and although the species is generally wind firm, it is subject to frequent storm damage.
The species is not listed as threatened federally in the US, but is listed as "Special Concern" in Kentucky, "Exploitably Vulnerable" in New York State, and "Threatened" in Tennessee.
The Committee on the Status of Endangered Wildlife in Canada placed the Butternut on the endangered species list in Canada in 2005.
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