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How to Manage Pests
UC Pest Management Guidelines
Spinach
Downy Mildew
Pathogen: Peronospora
farinosa f. sp. spinaciae
(Reviewed 11/05,
updated 11/05)
In this Guideline:
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SYMPTOMS
Initial symptoms of downy mildew consist of bright yellow spots that
form on cotyledons and leaves of all ages. With time, these spots can enlarge
and become tan and dry. Close inspection of the underside of the leaf often
reveals the purple growth of the fungus (sporangia and
sporangiospores). If disease development is
extensive, leaves appear curled and distorted and may take on a blighted effect
as a result of numerous infection sites.
COMMENTS ON THE DISEASE
Downy mildew is clearly the most widespread and destructive spinach
disease in California. Like all downy mildews, this pathogen requires cool, wet
conditions for infection and disease development. The heavy canopy of densely
planted spinach retains much moisture and creates ideal conditions for
infection and disease development. Spores (called sporangia) are dispersed in
the air from plant to plant and field to field by winds and splashing water. Peronospora
farinosa f. sp. spinaciae infects only spinach and a few Chenopodium weed
species. The pathogen exists as distinct genetic races.
In the field the pathogen can grow and spread rapidly, resulting
in widespread crop damage if environmental conditions are favorable. In
addition to loss of quality due to spots, the downy mildew infections can also
break down and rot if packed in bags and cartons.
MANAGEMENT
The use of resistant cultivars is the most effective means of
controlling spinach downy mildew. During the past 50 years in California, each
outbreak of a new downy mildew race was later matched by the development of
resistant spinach lines. A recent example of this pathogen/cultivar cycle took
place in early 1998 when race 4-resistant cultivars were infected by races
5 and 6. Researchers and plant breeders are currently developing cultivars
resistant to the new races. All foliar fungicide materials are protectants and
for best results must be applied before infection occurs and before symptom
development.
Organically Acceptable Methods
Cultural controls are acceptable for use on organically grown produce.
| Common Name |
Amount/Acre |
P.H.I.+ |
| (trade name) |
|
(days) |
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| A. |
MEFENOXAM |
up to 1 lb a.i./acre/season for all formulations |
21 |
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MODE OF ACTION: A PA(Group 4)1 acylalanine fungicide. |
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COMMENTS: A systemic fungicide applied to soil or plant
foliage. There are several use recommendations that apply to all Ridomil
formulations labeled for spinach. Do not exceed a total of 1.4 lb
a.i./acre/growing season when using a combination of Ridomil Gold EC, Ridomil
Gold GR, and Ridomil Gold/Copper. Plantback restrictions apply to some cereal
grains and other food and feed crops. None of these products are registered for use in a greenhouse. |
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(Ridomil Gold) EC |
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COMMENTS: This liquid formulation is an emulsifiable
concentrate and is registered for use in spinach as a soil application only.
Applications may be made banded over the row, preplant incorporated, or
injected with liquid fertilizer. Consult the label for specific application guidelines |
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...OR... |
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(Ridomil Gold) GR |
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COMMENTS: This is a granular formulation registered for use in
spinach as a soil application only. Applications may be preplant incorporated or preemergence. Consult the label for specific application guidelines. |
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...OR... |
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(Ridomil Gold/Copper) WP |
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COMMENTS: This combination is for foliar application to
spinach. Up to 2 applications are allowed per crop but curative applications
greatly increase the risk of the fungus developing insensitivity to this active ingredient. |
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| B. |
FOSETYL-AL |
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(Aliette 80 WDG) |
2–5 lb |
3 |
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MODE OF ACTION: A phosphonate (Group 33)1
fungicide.
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COMMENTS: A systemic fungicide applied to the foliage. Apply
when conditions favor disease development and continue on a 7–21 day
interval. Use sufficient water volume for good coverage. Do not exceed 7
applications per season. Do not apply in less than 10 GPA. Speckling on
leaves sometimes can occur after application with this product. Follow label
recommendations with respect to mixing compounds, buffers, surfactants, and other adjuvants. |
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| C. |
ACIBENZOLAR-S-METHYL |
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(Actigard) 50WG |
0.75 oz |
7 |
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(Blockade) 50WG |
0.75 oz |
7 |
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MODE OF ACTION: A benzo-thiadiazole (Group P)1
fungicide.
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COMMENTS: May cause leaf twisting or other growth responses.
Only for use in Santa Clara, Monterey, San Luis Obispo, Santa Barbara,
Ventura, Los Angeles, San Diego, Santa Cruz, San Benito, and San Mateo counties. See label for plantback restrictions. |
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| D. |
PHOSPHOROUS ACID |
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(Fosphite) |
1–2 qt |
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MODE OF ACTION: A phosphonate (Group 33)1
fungicide.
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COMMENTS: Do not apply with copper-based fungicides or
fertilizers. Allow 10 days before applying a copper-based compound to a crop
treated with this product or 20 days before applying this product to a copper-treated crop. |
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| E. |
COPPER HYDROXIDE |
Label rates |
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MODE OF ACTION: A multi-site contact (Group M)1
inorganic fungicide.
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COMMENTS: Copper sprays are only marginally effective even when several applications are made. |
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UC IPM Pest Management Guidelines: Spinach
UC ANR Publication 3467
Diseases
S. T. Koike, UC Cooperative
Extension, Monterey Co.
M. LeStrange, UC Cooperative Extension, Tulare Co.
F. F. Laemmlen, UC Cooperative Extension, Santa Barbara Co.
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