How to Manage Pests
UC Pest Management Guidelines
Carrot
Cercospora Leaf Blight
Pathogen: Cercospora carotae
(Reviewed 10/05,
updated 10/05)
In this Guideline:
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Cercospora blight can occur on any above ground carrot tissue.
However, symptoms are usually most severe and obvious along leaflet margins.
Infection sites initially appear as a brown spot with a dark brown margin. A
chlorotic halo often develops around these spots. As the disease progresses,
the leaflets become yellowed and curl at the margins. Lesions on leaf petioles,
stems, and flower parts are usually elongated and dark brown. Under heavy
disease pressure, severe loss of foliage may occur.
Cercospora blight is usually of minor importance in California but
often occurs in coastal carrot-growing regions. Cercospora carotae can be seedborne, but also survives between crops on
plant debris or in the soil. Infection occurs over a wide range of temperatures
with an optimum at 82°F.
Cultural Control
Use disease-free seed or treat seed with fungicides before planting.
Destroy diseased crop refuse by plowing it under to insure decomposition and
practice 2- to 3-year crop rotations.
Organically Acceptable Methods
Cultural controls are acceptable for use on organically grown produce.
Monitoring and Treatment Decisions
In fields with a history of Cercospora leaf blight, start fungicide
applications when conditions are conducive to disease development or when
disease is observed.
| Common name |
Amount/Acre |
P.H.I.+ |
| (trade name) |
|
(days) |
|
| Seed
Treatment
|
| A. |
THIRAM 50 WP |
8
oz/100 lb seed
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COMMENTS: Treated seed must not be used
for or mixed with food or animal feed. Treat only enough for immediate use;
do not store excess treated seeds beyond planting time.
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| After
Planting
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| A. |
AZOXYSTROBIN |
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(Quadris) |
9.2–15.4 fl oz |
0 |
| |
MODE
OF ACTION: A Qol (Group 11)1 fungicide.
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COMMENTS: Do not make more than one application
before rotating to a fungicide with a different mode of action. Do not make
more than four foliar applications of strobilurin fungicides per crop.
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| B. |
CHLOROTHALONIL |
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(Bravo Weatherstik) |
1.5-2 pt |
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MODE
OF ACTION: A multi-site contact (Group M)1 chloronitrile fungicide. |
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COMMENTS: Apply in sufficient water to
obtain good coverage. Repeat applications at 7- to 10-day intervals as needed
to maintain control. May be applied by sprinklers. Check the product label
for specific application requirements.
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| C. |
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: Repeat applications at 7- to
14-day intervals, depending on disease severity.
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| D. |
PYRACLOSTROBIN |
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(Cabrio) EG |
8–12 oz |
0 |
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MODE
OF ACTION: A Qol (Group 11)1 fungicide.
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COMMENTS: Do not make more than two
sequential applications before rotating to a fungicide with a different mode
of action. Do not make more than three applications of strobilurin fungicides
per crop.
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| E. |
TRIFLOXYSTROBIN |
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(Flint) |
2–3 oz |
7 |
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MODE OF ACTION: A Qol (Group 11)1 fungicide. |
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COMMENTS: To limit potential for resistance development do
not apply more than 3 sequential applications or a total of 4 applications
of all strobilurins per season. Do not apply more than 12 oz/acre/year. |
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UC IPM Pest Management Guidelines: Carrot
UC ANR Publication 3438
Diseases
R. M. Davis, Plant
Pathology, UC Davis
F. F. Laemmlen, UC Cooperative Extension, Santa Barbara Co.
J. Nunez, UC Cooperative Extension, Kern Co.
T. A. Turini, UC Cooperative Extension, Imperial Co.
Acknowledgment for contributions to the diseases section:
B. W. Falk, Plant Pathology, UC Davis
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