Michigan State University Extension
Ornamental Plants plus Version 3.0 - 00001680
11/12/99
Verticillium Wilt
Cause: Verticillium is a soil fungus that infects the
roots of a tree or shrub but does not cause a rot. The
fungus grows into the water- and food-conducting tissues
that feed a section of the plant. Thus, Verticillium wilt
often will occur on just one half or one section of a
tree, the section fed by the infected root. Plants may be
infected when bought from a nursery but show no symptoms.
The stress of transplanting then can cause collapse.
Symptoms: Infected trees do not grow well and may have
yellowed leaves, exhibit leaf scorch, have sparse crowns,
show branch dieback, or may set heavy crops of seed. On
severely infected trees the leaves on some branches may wilt
and die or the whole tree may wilt and die. The symptoms
may vary from year to year as trees can compartmentalize the
fungus if the tree is otherwise healthy.
Control: Remove severely infected plants and wilted branches
from surviving trees. Do not chip the wood but rather it
should be burned. Infested chips can cause the fungus to
spread to previously uninfected soil.
Plants with lighter infections should be watered regularly
during dry periods. Regular fertilization may help infected
trees compartmentalize the fungus. Apply the fertilizer in
the spring and use an equal analysis fertilizer such as 12-
12-12. Do not use high nitrogen fertilizer and be sure to
get the fertilizer 12 to 15 inches deep.
Resistant species can help reduce the incidence of
verticillium. The following genera and species are listed as
resistant. Some of the plants listed here have
characteristics that would make them relatively undesirable
as ornamentals.
Arborvitae (Thuja)
Beech (Fagus)
Birch (Betula)
Crab Apple (Malus)
Flowering Dogwood (Cornus florida)
Douglas-fir (Pseudotsuga)
Fir (Abies)
Ginkgo
Hackberry (Celtis)
Hawthorn (Crataegus)
Hickory (Carya)
Holly (Ilex)
Honeylocust (Gleditsia)
Hop Hornbeam (Ostrya)
Hornbeam (Carpinus)
Juniper (Juniperus)
Katsura Tree (Cercidiphyllum)
Larch (Larix)
European Mountain Ash (Sorbus aucuparia)
Mulberry (Morus)
White and Bur Oak (Quercus alba, Q. macrocarpa)
Pawpaw (Asimina)
Pine (Pinus)
London Planetree (Platanus acerifolia)
Poplar (Populus)
Pyracantha
Spruce (Picea)
Sweet Gum (Liquidambar)
Sycamore (Platanus occidentalis)
Willow (Salix)
Yew (Taxus)
Zelkova
Oak Wilt
Symptoms: Wilt, defoliation and the premature drop of
leaves help distinguish this vascular wilt from other
causes of wilting. In red oaks, the leaves may wilt and curl
and then fall to the ground or they may turn brown and stay
on the branches.
On white oaks the leaves will turn brown starting at the
leaf tip. Only a few branches will wilt and on these
branches the leaves will curl and stay on the tree.
Cause: Oak wilt is caused by a fungus carried by sap-
feeding beetles and certain other insects that visit
wounds in bark. The disease has caused serious losses in
Midwestern states, including Illinois and Wisconsin and
the Upper Peninsula of Michigan. Infected red oaks die
within a few weeks, but white oaks may linger on for two
to three years of decline. Studies in the Midwest have
determined that infection occurs from mid-May through
June. During this time, oaks should not be pruned,
climbed with shoe irons or otherwise wounded. The disease
can spread down a row of oaks as diseased roots infect
healthy roots of nearby trees. Roots of trees belonging
to one species often graft with one another, and this
facilitates disease spread.
Control: Infected trees should be removed and wood,
including stumps, split before April 1. Otherwise, the wood
will bloom with the fungus beneath the bark and insects will
seek the spores and carry them to healthy trees. If used for
firewood, the pile should be covered with a tarp and black
plastic and left until the following August. The bottom of
the tarp should be sealed with soil so that insects can not
get to the fungal pads that form on infected wood.
Closely planted trees should be treated to remove the
chance of root grafting. This is best done by passing a
root cutting blade 2 feet deep at the midpoint between the
trees. This severs root connections between trees.
Alternatively, a soil fumigant can be placed at an
appropriate concentration in holes 2 feet deep and 8
inches apart along the midpoint between two trees to kill
intermingling roots. Fumigants are not as effective as the
mechanical severing of roots, can cause damage to healthy
trees and must be carried out by a licensed professional
pesticide applicator.
Insects that carry the fungus will visit pruning wounds made
in early summer. Prune in winter and cover the wound with
pruning paint to help avoid oak wilt infections.
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to commercial products or trade names does not imply
endorsement by MSU Extension or bias against those not
mentioned. This information becomes public property upon
publication and may be printed verbatim with credit to MSU
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a commercial product or company.
This file was generated from data base ZZ on 01/19/00.
Data base ZZ was last revised on 11/12/99.
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