Vascular Wilts
Dutch Elm Disease - Symptoms and elm bark beetles
Leaf symptoms
Vascular discoloration in xylem after removing the bark. Heathy xylem would be white.
Elms respond to infection by producing vascular occlusions with host response chemicals (phenolics) and also morphological barriers like tyloses. Tyloses are cells along the vessels that balloon out into the vessel lumen causing a blockage.
Root graft between two elm trees.
European elm bark beetles
Egg laying galleries of the European elm bark beetle are made along with the grain of the wood (up and down)
Egg laying gallery of European elm bark beetle with larval galleries coming out from the sides of it.
Exit holes in the bark where mature elm bark beetles left the tree. Adult beetles carry the fungus causing Dutch elm disease from the diseased wood to healthy trees when they do their maturation feeding.
Feeding site at twig crotch caused by the European elm bark beetle. As the beetle feeds on the healthy tree, spores of the fungus enter the xylem of the elm.
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Native elm bark beetles
Egg laying galleries of native elm bark beetle. Direction of the main egg laying gallery is across the grain.
A relatively small branch with many North American elm bark beetle galleries. Even small diameter stems can be used for egg laying and lots of new beetles can emerge.
An elm log with galleries of both the European and North American elm bark beetles.
Elm bark
Tree inspectors often need to know how to identify elm in wood piles since having elm wood can serve as a place for bark beetles to bred. The bark of elm has very characteristic layering that other hardwood trees do not have.