UC IPM Online UC ANR home page UC IPM home page

UC IPM Home

Search

SKIP navigation
How to Manage Pests

Home & garden
Agriculture
Natural environments
Exotic & invasive

Weather data & products
Degree-days
Interactive tools & models

Identification Galleries

Natural enemies
Weeds

Educational Resources

Publications & more
Workshops and events
Training programs
Pesticide information

Research and IPM

Grants programs
Funded-project results

 
  Printer-friendly version

How to Manage Pests

UC Pest Management Guidelines

| More pests | More crops | About guidelines |

Irregular brown spots on carrot leaves and streaks on petioles caused by bacterial leaf blight.

Carrot

Bacterial Leaf Blight

Pathogen: Xanthomonas campestris pv. carotae

(Reviewed 1/09, updated 1/09)

In this Guideline:

SYMPTOMS

Bacterial leaf blight is often first noticed in fields as brown areas about 3 to 4 feet in diameter. Leaf symptoms appear as irregular brown spots, often beginning on the leaf margins. Lesions initially have an irregular, yellow halo and may appear watersoaked. Spots coalesce and cause a leaf blight and dark brown streaks develop on leaf petioles. Floral parts may also be blighted. A sticky amber-colored bacterial exudate, which is a diagnostic sign of the disease, may be present on leaves or observed flowing downward on petioles and flower stalks.

COMMENTS ON THE DISEASE

Xanthomonas campestris pv. carotae is seedborne and survives on and is spread with carrot seed. The bacteria also survive in carrot debris but cannot survive in the soil in the absence of debris. Rain or sprinkler irrigation is required for optimum disease development. Warm weather favors infection and disease development. Optimum temperatures are between 77° and 86°F; infection does not occur below 65°F. The pathogen is dispersed in splashing water. Plant-to-plant spread may occur under heavy dew conditions.

In most carrot-growing areas bacterial blight does not warrant control. In a few areas, such as the Antelope Valley, severe outbreaks may occur.

MANAGEMENT

Cultural Control
Plant Xanthomonas-indexed seed or treat seed in a hot water dip. Use furrow or drip irrigation rather than sprinklers. Turn under carrot residue to hasten decomposition. Avoid continuous carrot culture by using a 2- to 3-year crop rotation scheme.

Organically Acceptable Methods
Cultural controls, hot water dips, and sprays of certain copper sulfate formulations are acceptable for use on organically grown produce.

Monitoring and Treatment Decisions
Assay seed and treat if pathogen is found. Foliar treatments occasionally necessary if rainy weather persists.

Common name Amount/Acre R.E.I.+ P.H.I.+
(trade name)   (hours) (days)
When choosing a pesticide, consider information relating to environmental impact.
 
SEED TREATMENT
A. HOT WATER DIP#   NA NA
  COMMENTS: Soak seed in hot water (126°F; 52°C) for 25 minutes.
 
FOLIAR TREATMENT
A. COPPER SULFATE# Label rates 12 0
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M1)
  COMMENTS: Repeat applications at 7- to 14-day intervals, if necessary, to maintain control. Not all copper compounds are approved for use in organic production so be sure to check individual products.
 
B. COPPER HYDROXIDE
  (Champ, Kocide 2000, etc.) Label rates 24 0
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M1)
 
+ Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
# Acceptable for use on organically grown produce.
1 Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of actions (for more information, see http://www.frac.info/). Fungicides with a different group number are suitable to alternate in a resistance management program. In California, make no more than one application of fungicides with mode of action Group numbers 1, 4, 9, 11, or 17 before rotating to a fungicide with a different mode of action Group number; for fungicides with other Group numbers, make no more than two consecutive applications before rotating to fungicide with a different mode of action Group number.
NA Not applicable.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Carrot
UC ANR Publication 3438
Diseases
J. Nunez, UC Cooperative Extension, Kern County
R. M. Davis, Plant Pathology, UC Davis
T. A. Turini, UC Cooperative Extension, Fresno County
Acknowledgment for contributions to Diseases:
B. W. Falk, Plant Pathology, UC Davis
F. F. Laemmlen, UC Cooperative Extension, Santa Barbara County

Top of page

Statewide IPM Program, Agriculture and Natural Resources, University of California
All contents copyright © 2009 The Regents of the University of California. All rights reserved.

For noncommercial purposes only, any Web site may link directly to this page. FOR ALL OTHER USES or more information, read Legal Notices. Unfortunately, we cannot provide individual solutions to specific pest problems. See How to manage pests, or in the U.S., contact your local Cooperative Extension office for assistance. /PMG/r102100811.html revised: January 26, 2009. Contact webmaster.