How to Manage Pests

UC Pest Management Guidelines

I have had a number of requests to identify fruit spotting on lemons.  It turns out to be Septoria fungus which can show up on leaves, stems and fruit.  The key to this is to make sure there is a fungicide on the  tree in the fall before the wet weather kicks in

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