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How to Manage Pests
UC Pest Management Guidelines
Floriculture and Ornamental Nurseries
Verticillium Wilt
Pathogens: Verticillium dahliae and V. albo-atrum
(Reviewed 1/02,
updated 1/02)
In this Guideline:
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SYMPTOMS
Symptoms vary somewhat with the kind of plant and the environment, but some
symptoms are common to most situations. The leaves may wilt and turn yellow,
first at the margins and between the veins, then they turn tan or brown and die
starting from the base to the tip of the plant or branch. Dead leaves usually
fall; sometimes they remain attached. Woody plants often are affected first on
one side, and affected branches usually die. The water-conducting tissues
(sapwood) of infected plants are often discolored with
dark streaks occurring in the
xylem tissue; discoloration varies with the species but frequently is an olive green, dark brown, or
black. In some plants there is little or no discoloration (including olive,
ash, and roses).
COMMENTS ON THE DISEASE
Verticillium wilt, one of the most wide-spread and destructive soilborne
diseases of plants, affects a large number of herbaceous and woody species
throughout the world. The causal fungus, Verticillium dahliae, infects
susceptible plants through the roots and plugs the water conducting tissues.
Susceptible flower crops include China aster, chrysanthemum, cineraria, dahlia,
geranium, gerbera, heather, marigold, peony, pelargonium, rose, snapdragon,
statice, stock, and strawflower. The V. dahliae fungus forms microscopic
black resting structures (microsclerotia) capable of surviving in soil for many years in the absence of a
susceptible plant. When a susceptible plant is planted in soil infested with
the fungus, the microsclerotia germinate and infect the plant. Long rotations
with nonsusceptible plants are not effective in controlling the fungus.
The fungus also produces conidia that can be transported in irrigation water;
however, they are not long-lived. The fungus can be disseminated by leaves
dropping from infected plants and being blown around by the wind.
MANAGEMENT
Many horticultural crop plants have been selected or bred for resistance to the
fungus. Use resistant cultivars and pathogen-free plants whenever possible.
Avoid fields previously used for susceptible crops (eg. tomato, cotton,
potatoes, strawberries, as well as the ornamentals listed above). Remove and
destroy any plants that exhibit symptoms of Verticillium wilt. Soil fumigation
or soil solarization in sunny climates can be useful.
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Amount to Use |
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SOIL FUMIGATION |
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METHYL BROMIDE*/CHLOROPICRIN* |
Label rates |
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COMMENTS: Inject into soil and cover immediately with
plastic tarps. Planting can take place a few days after removal of
plastic covers; a few plants, however, (e.g., Alliums, carnations,
and snaps) are sensitive to and may be damaged by inorganic bromide
that remains in soil. For sensitive species, leach the bromide from
the soil with water before planting. Methyl bromide does not usually
kill all of the microsclerotia of Verticillium dahliae, the
fungus that causes Verticillium wilt. When this disease occurs it
is necessary to include chloropicrin in the fumigant. |
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Permit required from county agricultural commissioner
for purchase or use. |
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UC IPM Pest Management Guidelines: Floriculture and Ornamental Nurseries
UC ANR Publication 3392
Diseases
R. D. Raabe (emeritus), Environmental Science, Policy, and Management (ESPM),
UC Berkeley
M. E. Grebus, Plant Pathology, UC Riverside
C. A. Wilen, UC IPM Program, UC Cooperative Extension, San Diego Co.
A. H. McCain (emeritus), Environmental Science, Policy, and Management (ESPM),
UC Berkeley
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