An elm bark beetle's life revolves around elm trees. It breeds in
dead and dying elms, and depends exclusively on elm tissue for food,
this creates a devastating cycle for elms, when the Dutch elm disease
fungus Ophiostoma nova ulmi becomes part of the cycle. Thousands
of eggs can be laid by the adult females in one piece of wood the
size of a fireplace log. If the tree died from Dutch elm disease
every beetle that hatches and emerges as an adult from that wood
may be carrying the fungus. They will be looking for a healthy elm
on which to feed and will inadvertently inoculate the tree with
Dutch elm disease via the spores carried on their bodies. The majority
of new infections, and the bulk of the losses to Dutch elm disease,
are due to this method of transmission. That is why prompt detection,
removal, and destruction of dying elms is so critically important.
This
wound on this small 4 year old twig was caused by a beetle that
introduced Dutch Elm disease to this tree.
The
Beetle Scolytus multistriatus spreads the disease from
sick to healthy Elms
Root
grafts can also spread the disease from sick to neighboring
healthy elms
Root Graft Spread of
Dutch Elm Disease
The other method of disease transmission between elms is through
grafted roots. When elms
are growing near each other their roots come in contact in the
soil and graft together. In the absence of a vascular wilt disease
such as Dutch Elm disease, this is an advantage for the trees.
The Dutch Elm disease fungus however can pass from diseased
to healthy trees through these grafted roots and continue to
spread indefinitely through a stand of elms.
