56 Nebraskaland • June 2019
O ak wilt is a serious fungal disease that threatens
Nebraska oak trees (Quercus spp.). Oak wilt damages the
vascular system of the oak tree, disrupting the flow of water
and nutrients, and can ultimately kill an infected oak tree. It
has been confirmed in 24 states, including Nebraska.
Trees in the red oak group, which includes red and pin
oaks, are highly susceptible to oak wilt. The white oak
group, including bur, swamp white and white oak, are less
susceptible.
Infection of red oaks most often occurs in spring and early
summer, and leads to rapid death. Leaves of infected trees
may turn bronze to tan, starting at the leaf tip and moving
back toward the base. Rapid leaf drop is another indicator of
an oak wilt infection. Peeling bark from infected branches
will reveal black to gray vascular discoloration, another
symptom of an oak wilt infection.
Symptoms in white oaks often appear later in the season
and progress more slowly. Infected white oaks may show leaf
drop and branch dieback for several years before dying.
Infected trees will produce a fungal mat under the bark.
Pressure caused by the fungal mat causes the bark to split,
and the spores to become exposed. Sap beetles are attracted
to these wounds and the sweet scent of the spores. The
spores are sticky and become attached to the beetles as they
feed. The beetles then carry the oak wilt spores on their
bodies to uninfected trees, where they cause new infections.
Root grafts, where the roots of two trees fuse together, can
also spread oak wilt.
There is no cure for oak wilt. To minimize the risk of
spreading the disease, avoid pruning oak trees between
April and July, as the pruning wounds may attract beetles.
Infected logs and firewood can disperse spores to uninfested
areas as well. Don't move firewood. Help protect Nebraska's
trees by getting your firewood where you plan to burn it.
PROTECT OUR OAK
By Julie Van Meter, State Entomologist, Nebraska
Department of Agriculture
INFECTED
LEAVES.
PHOTO
BY
C.E.
SELISKAR,
BUGWOOD.ORG
MIXED BAG
