How to Manage Pests

UC Pest Management Guidelines

Citrus

Septoria Spot

Pathogen: Septoria citri

(Reviewed 9/08, updated 9/08)

In this Guideline:


Symptoms

Early symptoms of Septoria spot appear as small, light tan to reddish brown pits on fruit, 0.04 to 0.08 inch (1 to 2 mm) in diameter, which usually do not extend beyond the oil-bearing tissue. Advanced lesions are blackish, sunken, extend into the albedo (white spongy inner part of rind), and are up to 0.8 to 1.2 inch (20 to 30 mm) in diameter. Dark brown to black fruiting bodies often develop in these lesions, which usually do not extend beyond the oil-bearing tissue. The spots are much more conspicuous after the fruit has changed from green to yellow or orange. Small spots may develop into large, brown blotches during storage or long-distance transportation. Septoria citri may also cause similar spotting on leaves or twigs that are weakened by frost or pests.

Comments on the Disease

The Septoria fungus causes spotting of Valencia oranges, late-season navel oranges, and occasionally of lemons and grapefruit. It occurs in the San Joaquin Valley and interior districts of southern California during cool, moist weather.

Infections begin when Septoria conidia are transported throughout the tree by rainfall. The spores germinate with additional moisture from rain or dews and commonly infect cold-injured fruit tissue and mechanical injuries. The damage to the rind lowers the grade of the fruit and results in culling.

Septoria spot may be confused with copper injury and other abiotic and biotic agents.

Management

Apply a preventive copper spray in late fall or early winter, just before or after the first rain. In years with heavy rainfall, additional applications may be necessary.

For California oranges (Navels and Valencias) shipped to Korea:

  • Make the first spray between October 15 and November 30.
    • Use a minimum of 2.5 lb metallic zinc equivalent per acre and a minimum of 1.65 lb metallic copper equivalent per acre. When using 1.65 lb copper equivalent use a minimum of 2 lb hydrated lime, and when using 4 lb copper equivalent, use a minimum of 4 lb hydrated lime.
    • Apply as a dilute application with a minimum of 400 gallons per acre.
    • Higher rates of zinc, copper, and lime may be used as local conditions warrant but do not exceed manufacturer's label rates.
    • Bordeaux sprays also meet the preharvest requirements for exporting oranges to Korea. Use a minimum of 3.3 lb metallic zinc, 1.65 lb metallic copper, and 20 lb hydrated lime in no less than 400 gallons per acre. Mix in following order: zinc, then copper, followed by lime.
  • Cover the entire tree canopy; skirt sprays are not acceptable.
Common name Amount to use R.E.I.‡ P.H.I.‡
(example trade name)   (hours) (days)

  Calculate impact of pesticide on air quality
 
When choosing a pesticide, consider the general properties of the fungicide as well as information relating to environmental impact. Not all registered pesticides are listed. Always read label of product being used.
 
A. FIXED COPPER+ZINC SULFATE+HYDRATED LIME# See comments See comments
  MODE OF ACTION GROUP NAME (FRAC NUMBER1): Multi-site contact (M1)
  COMMENTS: Use rates under MANAGEMENT for oranges to be exported to Korea. Not all copper compounds are approved for use in organic production; be sure to check individual products. For tank mixes, observe all directions for use on all labels, and employ the most restrictive limits and precautions. Never exceed the maximum a.i. on any label when tank mixing products that contain the same a.i. Use the restricted entry interval and preharvest interval of the product with the most restrictive label of those used in the tank mix.
 
B. ZINC SULFATE+COPPER SULFATE+HYDRATED LIME#
  (3-2-6-100) 10–25 gal/tree See comments See comments
  MODE OF ACTION GROUP NAME (FRAC NUMBER1): Multi-site contact (M1)
  COMMENTS: For use on grapefruit, oranges, and lemons. Apply in 100 gal water from Oct.–Dec. or just before or after first rain. In the Central Valley increase the amount of hydrated lime to 20 lb for the control of leafhoppers, if populations of this pest are high; if populations are low, use the 6 lb rate. Hydrated lime helps prevent copper toxicity under certain environmental conditions. Use rates under MANAGEMENT for oranges to be exported to Korea. For information on making Bordeaux mixture, see UC IPM Pest Note: Bordeaux Mixture, ANR Publication 7481. Be sure to follow label directions as well. For tank mixes, observe all directions for use on all labels, and employ the most restrictive limits and precautions. Never exceed the maximum a.i. on any label when tank mixing products that contain the same a.i. Not all copper compounds are approved for use in organic production; be sure to check individual products. Use the restricted entry interval and preharvest interval of the product with the most restrictive label of those used in the tank mix.
 
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.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Citrus
UC ANR Publication 3441

Diseases

  • J. E. Adaskaveg, Plant Pathology, UC Riverside
Acknowledgment for contributions to Diseases:
  • J. A. Menge, Plant Pathology, UC Riverside
  • H. D. Ohr, Plant Pathology, UC Riverside

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