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How to Manage Pests
UC Pest Management Guidelines
Floriculture and Ornamental Nurseries
Downy Mildew
Pathogens:
Peronospora spp., Plasmopara spp., and Bremia sp.
(Reviewed 3/09,
updated 3/09)
In this Guideline:
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The name downy mildew is somewhat descriptive of the appearance of
the white, lavender, or purple sporulation that occurs usually
on the undersides of leaves. Downy mildew leaf lesions are often angular in
shape and delimited by veins. Pale yellow or
necrotic areas
often are visible from the upper side of the leaf. Extensive disease can result
in the death of large portions of the leaves.
In some plants when young shoots are infected the fungus may
become systemic and the resultant growth is stunted, malformed, and discolored.
In contrast with powdery mildews, the
downy mildews are more host specific and require very wet conditions to flourish.
Water is required for infection and humidity above 90% is needed for
sporulation. Growth of the pathogens is favored by cool temperatures.
Downy mildew spores are usually short-lived although they may
survive several days under cool, moist conditions. They are airborne and when
they land on a susceptible plant and there is free water, germination and
infection occurs, generally in 8 to 12 hours. Some downy mildews also produce a
sexual spore that can survive dry conditions, which enables the pathogen to
survive in the absence of the host. Downy mildews are favored by moist and cool
conditions (40° to 60°F).
| Common name |
Amount to Use |
R.E.I.+ |
| (trade name) |
|
(hours) |
|
| When choosing a fungicide, consider the general
properties of the fungicide as
well as information relating to environmental impact. |
| |
| A. |
MANCOZEB |
| |
(Dithane) 75 |
1–1.5 lb/100 gal water |
24 |
| |
MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M3) |
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COMMENTS: A protectant fungicide. Thorough coverage is important for control. |
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| B. |
MEFENOXAM |
| |
(Subdue Maxx) |
1-2 oz/100 gal water |
48 |
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MODE OF ACTION GROUP NAME (NUMBER1): Phenylamide (4) |
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COMMENTS: Use allowed in California under a 24(c) registration. |
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| C. |
COPPER 50%# |
1–2 lb/100 gal water |
24 |
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MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M1) |
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COMMENTS: A protectant fungicide. Growth of some plants may be
reduced by this material; follow label directions carefully to reduce the
risk of phytotoxicity. Not all copper compounds are approved for use in organic production; be sure to check individual products. |
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| D. |
FOSETYL-AL |
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(Aliette) |
2.5 lb/100 gal water |
12 |
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MODE OF ACTION GROUP NAME (NUMBER1): Phosphonate (33) |
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COMMENTS: For control of downy mildew on roses. Spray to wet using no more than 400 gal/acre. |
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UC IPM Pest Management Guidelines: Floriculture and Ornamental Nurseries
UC ANR Publication 3392
Diseases
S. T. Koike, UC Cooperative Extension Monterey County
C. A. Wilen, UC IPM Program, UC Cooperative Extension San Diego County
Acknowledgment for contributions to Diseases:
R. D. Raabe, (emeritus) Environmental Science, Policy, and Management (ESPM), UC Berkeley
A. H. McCain, (emeritus) Environmental Science, Policy, and Management (ESPM), UC Berkeley
M. E. Grebus, Plant Pathology, UC Riverside
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