Fall (October) is a great
time to plant trees, but it is also important that we protect
the trees that we have. The major disease threat to live and
red oak trees in our area is oak wilt. The disease is
expressed in red oaks (Texas, Schumard, Blackjack) by a
healthy tree showing fall-like coloring in late spring or
early fall and dying. The live oak usually dies slower (2
months to two years after showing initial symptoms), an
agonizing time for the tree's owner because once symptoms are
evident there is nothing to do to save the tree. Watch for the
characteristic veinal necrosis on leaves from infected live
oaks. The area on the veins is red, brown, or yellow and the
area in between is green.
Oak wilt is easy to prevent
and difficult to treat. Because the disease travels through
the interconnected roots of live oaks at 100 feet per year
once the infection is in a neighborhood, you must trench a
break in the roots around the infected trees (plus 100 feet).
Trenching is disruptive, expensive, and difficult in an urban
neighborhood. Everybody must cooperate and tolerate the
removal of fences, shrubs, outbuildings, etc.
Individual trees can be
protected with the chemical Alamo injected by a trained
applicator but it is also expensive (approximately $7 to $18
per inch of diameter). It protects the tree from infection but
does not stop the spread of the disease or cure the infected
tree.
Prevent the diseases spread
by painting all wounds on live oaks and red oaks. Keep a spray
can of pruning paint in your garage to immediately paint any
wound on your trees. Pruning, weed-eater and machinery cuts on
the trunk and exposed roots are especially susceptible to
infection. Sap beetles carry the disease spores from an
infected red oak to the wound on a live or red oak. The paint
stops them. Every minute you wait after the wound occurs
increases the chance of infection. The first two days are most
critical. We no longer say there are windows of safety because
of cold weather or hot weather. Central Texas weather is too
unpredictable and changeable--paint every wound all year long.
Firewood from red oaks can
also rarely be a source of the oak wilt infection. Protect
your neighborhood by managing firewood to avoid infection. It
is not necessary to reduce the use of the fireplace in order
to stop the spread of oak wilt. Smoke from infected wood
burning is NOT a threat! The fungus is destroyed by heat and
will not even survive in dry firewood. If you utilize red oak
firewood, try to purchase wood from trees that have not been
infected or killed from oak wilt. Only wood that has been
cured for an entire summer should be stored in the vicinity of
uninfected red or live oaks. If you bought oak firewood for
this winter and are unsure of its age or origins, use it up
before spring.
