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How to Manage Pests
UC Pest Management Guidelines
Cucurbits
Powdery Mildew
Pathogens: Sphaerotheca fuliginea (=Podosphaera xanthii) and Erysiphe cichoracearum (=Golovinomyces cichoracearum)
(Reviewed 12/09,
updated 12/09)
In this Guideline:
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All cucurbits are susceptible to powdery mildew, but the disease is
less common on watermelon than on other cucurbits. Powdery mildew first appears
as pale yellow spots on stems, petioles, and leaves. These spots enlarge as the
white, fluffy mycelium grows over plant surfaces and produces spores, which
give the lesions a powdery appearance. Affected leaves become dull, chlorotic,
and may show some degree of wilting in the afternoon heat; eventually they
become brown and papery.
Powdery mildew of cucurbits may occur at any time in coastal and
desert production areas but is more common in fall in the San Joaquin Valley
and Sacramento Valley. The disease may be caused by one of two species of mildew
fungi, although E. cichoracearum is rare. Several races of each fungus also
exist. The pathogens generally overwinter on weeds and their spores can be
carried long distances by air currents. Infection is favored by high humidity
(50 to 90%), and disease development is favored by vigorous plant growth and
moderate temperatures.
Plant resistant varieties, follow good sanitation practices, and
control weeds. Carefully monitor fields, even those with powdery mildew resistant
varieties, because there is recent evidence that plant resistance-breaking
races are present in California. If multiple fungicide applications are needed
to control powdery mildew, alternate materials with different modes of action
especially if using fungicides with medium to high resistance potential
(azoxystrobin-Quadris, myclobutanil-Rally, pyraclostrobin –Cabrio,
pyraclostrobin/boscalid-Pristine, trifloxystrobin-Flint, and
trifumizole-Procure). Apply a treatment when disease symptoms first occur and
repeat if symptoms reappear.
| Common name |
Amount/Acre |
R.E.I.+ |
P.H.I.+ |
| (trade name) |
|
(hours) |
(days) |
|
| Not all registered pesticides are listed. Always read label of product
being used. |
| |
| A. |
TRIFLUMIZOLE |
| |
(Procure) 50WS or 480SC |
4–8 oz or 4-8 fl oz |
12 |
0 |
| |
MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3) |
| |
COMMENTS: Do not apply more than 40 oz of Procure 50WS or 40 fl oz of Procure 480SC/acre/season. |
| |
| B. |
MYCLOBUTANIL |
| |
(Rally) 40W |
2.5–5 oz |
24 |
0 |
| |
MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3) |
| |
COMMENTS: Do not apply more than 1.5
lb/acre/season. |
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| C. |
PYRACLOSTROBIN/BOSCALID |
| |
(Pristine) |
12.5–18.5 oz |
12 |
0 |
| |
MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) and Carboxamide (7) |
| |
COMMENTS: Do not make more than one application before
alternating to a fungicide with a different mode of action other than Group 11. |
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| D. |
MICRONIZED SULFUR# |
| |
(Microthiol) |
4–6 lb |
24 |
0 |
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MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M2) |
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COMMENTS: Thiolux is not labeled for pumpkins but Microthiol
is. Sulfur can injure plants, especially when temperatures reach 95°F. Do not use on sulfur-sensitive varieties. |
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| E. |
QUINOXYFEN |
| |
(Quintec) |
4–6 fl oz |
12 |
3 |
| |
MODE OF ACTION GROUP NAME (NUMBER1): Quinoline (13) |
| |
COMMENTS: Registered for use on melons, including cantaloupe and watermelon. Do not apply more than 24 fl oz/acre/season. |
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| F. |
AZOXYSTROBIN |
| |
(Quadris) |
11–15.4 fl oz |
4 |
1 |
| |
MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) |
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COMMENTS: Do not apply more than one application before rotating to a fungicide with a different mode of action (i.e., group number) |
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| G. |
TRIFLOXYSTROBIN |
| |
(Flint) |
1.5–2 oz |
12 |
0 |
| |
MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) |
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COMMENTS: Do not apply more than one application before rotating to a fungicide with a different mode of action (i.e., group number) |
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| H. |
PYRACLOSTROBIN |
| |
(Cabrio) |
16 oz |
12 |
0 |
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MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) |
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COMMENTS: Do not apply more than one application before rotating to a fungicide with a different mode of action (i.e., group number). |
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| I. |
KRESOXIM-METHYL |
| |
(Sovran) |
3.2 -4.8 oz |
12 |
0 |
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MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) |
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COMMENTS: Do not apply more than one application before rotating to a fungicide with a different mode of action (i.e., group number). |
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| J. |
POTASSIUM BICARBONATE# |
| |
(Kaligreen) |
2.5–5 lb |
4 |
1 |
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MODE OF ACTION: An inorganic salt. |
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COMMENTS: Use the higher rate when disease pressure is severe.
Direct contact with the fungus is required for control. Conditionally allowed in an organically certified crop; check with your certifier. |
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| K. |
CINNAMALDEHYDE |
| |
(Cinnacure) |
0.25–1 gal |
4 |
0 |
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MODE OF ACTION: A botanical fungicide. |
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COMMENTS: Make no more than two consecutive applications
before rotating to a fungicide with a different mode of action. May not provide good control under all conditions. |
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UC IPM Pest Management Guidelines: Cucurbits
UC ANR Publication 3445
Diseases
R. M. Davis, Plant Pathology, UC Davis
T. A. Turini, UC Cooperative Extension, Imperial County
B. J. Aegerter, UC Cooperative Extension, San Joaquin County
J. J. Stapleton, UC IPM Program, Kearney Agricultural Center, Parlier
Acknowledgment for contributions to Diseases:
W. D. Gubler, Plant Pathology, UC Davis
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