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How to Manage Pests
UC Pest Management Guidelines
Floriculture and Ornamental Nurseries
Rust
Pathogens: Puccinia spp. and others
(Reviewed 1/02,
updated 1/02)
In this Guideline:
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SYMPTOMS
Rust pustules appear as powdery masses of yellow, orange, purple, black, or
brown spores on leaves and sometimes on stems. Pustules are usually found on
the undersides of leaves.
COMMENTS ON THE DISEASE
The rust fungi are obligate parasites in the order Uredinales. Many have
complicated life cycles that include four different spore stages and two
distinctly different hosts. Other rusts produce all or sometimes only one type
of spore and infect only one kind of plant. Stem rust (Puccinia graminis)
of wheat alternates between barberry (Berberis spp.) and
wheat (Triticum vulgare) and all four spore stages are produced. Rose
rust also produces all four spore stages but only roses (Rosa spp.) are
infected.
Uredospores ("repeating" spores) are produced in pustules that appear yellow,
orange, or brown as a result of masses of spores. Uredospores are windborne and
infect the plant through stomata. Water is required for short periods (6-8
hours or less) for germination and infection. Heavy dew is often sufficient.
Once infection has occurred, water is no longer needed for the continued
development, and the infection and spore production will continue for the life
of the leaf.
Some rusts, including rose rust (Phragmidium mucronatum), may survive
the winter on leaves that do not fall. Rose rust also survives as teliospores
(dark, overwintering spores) that form in fall. These spores survive in a
dormant stage on fallen leaves. It is recommended that leaves with teliospores
be removed, rapid composted, or buried.
MANAGEMENT
Rust diseases are favored by moderate temperatures that favor the growth of the
host. Rust spores can be killed by high temperatures. Some rust infections,
such as geranium rust (Puccinia pelargoni-zonalis), can be eradicated by
hot water treatment of cuttings, but some damage to the host can occur.
Because water is necessary for infection, overhead irrigation should be avoided
when rust is a problem. If possible, eliminate alternate hosts if they occur
and prune off infected stalks.
Chrysanthemum white rust, caused by Puccinia horiana, is under
an eradication program in California. If you have this disease contact
your agricultural commissioner. See specific guidelines under the DISEASE
CONTROL OUTLINE FOR CHRYSANTHEMUM.
CONTROL
There are several fungicides that can be used to protect plants from infection.
Mancozeb as a protectant and myclobutanil as an eradicant are generally
effective against all rusts while triadimefon is effective against only
specific rusts.
Common name
(trade name) |
Amount to Use
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| A. |
MANCOZEB |
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(Dithane) 75W |
1-1.5 lb/100 gal water
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COMMENTS: Provides protection only; must be applied before
infection. |
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| B. |
MYCLOBUTANIL |
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(Systhane) 40WSP |
4 oz/100 gal water
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| C. |
TRIADIMEFON |
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(Strike, Bayleton) 25WDG |
2-4 oz/100 gal water
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COMMENTS: Because this material is closely related to
growth retardant materials, it can have a toxic effect on certain
plants, such as greenhouse roses. Provides general control of some
rusts. |
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| D. |
AZOXYSTROBIN |
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(Heritage) |
1-4 oz/100 gal water
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COMMENTS: Apply as a broadcast or banded spray targeted
at the foliage or crown of the plant. |
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| E. |
WETTABLE SULFUR |
1-3 lb/100 gal water
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COMMENTS: Use a wetting agent. Not as effective as other
materials. |
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| F. |
CHLOROTHALONIL* |
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(Daconil Zn) 38.5% |
23-32 fl oz/100 gal water
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COMMENTS: Provides protection only; must be applied before
infection. |
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| G. |
PROPICONAZOLE |
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(Banner Maxx) |
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COMMENTS: Controls white rust of chrysanthemums but may
cause phytotoxic symptoms on some cultivars. |
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| H |
NEEM OIL |
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(Triact) 90EC |
Label rates
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COMMENTS: Registered for landscape and nursery ornamentals,
neem has some protectant properties against rust, but is not effective
for rust on rose. Apply on a 14-day schedule. |
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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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