Field guide to exotic pests and diseases: Chestnut blight

Cryphonectria parasitica (Murr.) Barr.

Typical young cankers on American chestnut

Orange-red fruiting bodies on American chestnut

Distribution: Japan, China, Korea, USA, Canada, Italy and throughout Europe.

Hosts: chestnut, oak, red maple, shagbark hickory, and eucalyptus.

Signs: characterised by cankers that kill bark and usually cambium and sapwood of twigs, branches, and trunks. Leaves and shoots wilt and die. From a distance, the prominent signs are yellow and brown leaves on one or more branches and eventually dead leafless branches. Typical canker on young, smooth-barked stems are recognised by the yellow-brown to orange surface colour representing the small fruiting structures of the pathogen. Cankers on thick barked trees are inconspicuous until splits and cracks expose the buff-coloured inner bark. Adventitious sprouts may develop from below a canker indicating its position on the host. Entire trees may die if the trunk is girdled.

Likely pathway: nuts/seeds, nursery stock, bark, lumber and wood packaging material including dunnage.

Potential impact: one of the most serious plant diseases in North America. Within 50 years the disease spread to the extremes of the natural range of the American chestnut, destroying the economic and aesthetic value of one of America’s most versatile trees.

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