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How to Manage Pests
UC Pest Management Guidelines
Avocado
Verticillium
Wilt
Pathogen: Verticillium
dahliae
(Reviewed 1/07,
updated 1/07)
In this Guideline:
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The entire tree or only one or several branches wilt suddenly when
infected with Verticillium. Leaves turn
brown and die, but the dead leaves usually remain on the tree for several
months. Brown to gray-brown streaks are
visible in the xylem of the branches or roots when the bark is removed. Trees
with Verticillium wilt often send
out new, vigorous shoots within a few months after the initial wilting. If well
cared for, affected trees often recover completely with no reoccurrence of the
disease. However, not all trees survive an infection and disease symptoms sometimes
reoccur after an apparent recovery.
Verticillium dahliae fungus
infects many hosts, including various berry and flower crops, cotton, eggplant,
olive, pepper, stone fruit trees, strawberry, and tomato. Verticillium wilt is present throughout the state but is less
common in avocado than root rot and canker diseases. Verticillium
dahliae persists for years as microsclerotia
in soil. Microsclerotia and spores move in water and wind and spread in
infested organic matter and soil that is moved. The fungus infects through
feeder roots, and then moves up in the water-conducting xylem system, retarding
or preventing water movement to foliage from the roots.
No known methods are effective in curing infected trees. Trees often
recover completely and display no further symptoms, even though they are still
infected. After dieback ceases and new growth begins, prune off dead branches.
Provide optimal irrigation and modest fertilization to promote new growth. If
a tree dies from Verticillium, remove it
and replant with a nonhost crop or fumigate the planting hole and surrounding
soil before replanting with avocado. In areas where V. dahliae is known
to occur, plant Mexican rootstocks instead of the more Verticillium-susceptible
Guatemalan rootstocks. Do not plant avocado on land where crops susceptible to Verticillium wilt
have previously grown. Do not interplant avocado with other hosts of Verticillium, which
are listed in publications such as Plants
Resistant or Susceptible to Verticillium Wilt (UC
ANR Publication 2703). Even if they have recovered, do not use trees that have
been affected with Verticillium wilt as
a source of budwood or seed.
Common name
(trade name) |
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| Amount to Use |
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| When choosing a pesticide, consider information relating
to environmental quality. |
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| A. |
METHYL BROMIDE* |
350-450
lb/acre or
1 lb/100 sq ft |
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COMMENTS: Use allowed only under a
Critical Use Exemption permit. Use low rate on sandy loam and high rate on
heavier soils with high clay content. Inject 7-8 inches, 12-18 inches apart,
and tarp immediately. Do not plant for at least 1 month. Fumigants such as
methyl bromide are a prime source of volatile organic compounds (VOCs), which
are a major air quality issue. Fumigate only as a last resort when other management strategies have not been successful or are not available. |
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UC IPM Pest Management Guidelines: Avocado
UC ANR Publication 3436
Diseases
B. A. Faber, UC Cooperative
Extension, Santa Barbara/Ventura counties
G. S. Bender, UC Cooperative Extension, San Diego County
H. D. Ohr (emeritus), Plant Pathology, UC Riverside
Acknowledgment for contributions to the diseases section:
L. J. Marais, Plant Pathology, UC Davis
J. A. Menge, Plant Pathology, UC Riverside
R. Hofshi, Hofshi Foundation, Fallbrook, CA
J. S. Semancik, Plant Pathology, UC Riverside
J. A. Downer, UC Cooperative Extension, Ventura County
U. C. Kodira, Plant Pathology, UC Davis
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