Symptoms and Signs
Early symptoms of Septoria spot appear as small, light tan to reddish brown pits on fruit, 0.04 to 0.08 inch (1–2 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 (20–30 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, 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 disseminated throughout the tree by rainfall. The spores germinate with additional moisture from rain or dew 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 manufacturers' 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 | REI‡ | PHI‡ | |
|---|---|---|---|---|
| (Example trade name) | (hours) | (days) | ||
| Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least likely to cause resistance are at the top of the table. When choosing a pesticide, consider information relating to the pesticide’s properties and application timing, honey bees, and environmental impact. Always read the label of the product being used. | ||||
| A. | FIXED COPPER/ZINC SULFATE/HYDRATED LIME# | See comments | See comments | See comments |
| MODE-OF-ACTION GROUP NAME (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 (NUMBER1): Multi-site contact (M1) | ||||
| COMMENTS: For use on grapefruit, oranges, and lemons. Apply in 100 gal water from October through December 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 numbers of this pest are high; if numbers 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 (Total amount (lb/acre): Metallic Zn 2.5–4, Cu 1.65–3, and Lime 2–4 lbs). 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. | ||||
| C. | AZOXYSTROBIN/DIFENCONAZOLE | |||
| (Quadris Top) | 10–15.4 fl oz | 12 | 0 | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) and demethylation inhibitor (DMI) (3) | ||||
| COMMENTS: Apply in a 7- to 21-day interval. Do not apply more than 61.5 fl oz of product per season or 0.5 and 1.5 lb of difenoconazole or azoxystrobin, respectively, per crop. Do not make more than two sequential applications before rotating to a non-QoI group. May be applied by ground or by air. Use a sufficient amount of water to provide thorough coverage. Use a minimum of 10 gal/acre for aerial applications. | ||||
| D. | FLUOPYRAM/TRIFLOXYSTROBIN | |||
| (Luna Sensation) | 5.0–7.6 fl oz | 12 | 7 | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): Succinate dehydrogenase inhibitor (SDHI) and quinone outside inhibitor (11). | ||||
| COMMENTS: Apply in a 7- to 21-day interval. Do not apply more than 27.1 fl oz of product per season or 0.446 and 0.5 lb of fluopyram or trifloxystrobin, respectively, per acre per year. Do not make more than two sequential applications before rotating to a non-SDHI (7) or non-QoI (11) group. May be applied by ground, air, or chemigation. Use a sufficient amount of water to provide thorough coverage. Use a minimum of 10 gal/acre for aerial applications. | ||||
| E. | FLUXAPYROXAD/PYRACLOSTROBIN | |||
| (Priaxor) | 5.5–6.5 fl oz | 12 | 0 | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): Succinate dehydrogenase inhibitor (SDHI) and quinone outside inhibitor (11). | ||||
| COMMENTS: Apply in a 10- to 21-day interval. Do not apply more than 44 fl oz of product per season or no more than four applications per year. Do not make more than two sequential applications before rotating to a non-QoI or non-SDHI groups. May be applied by ground or by air. Use a sufficient amount of water to provide thorough coverage. Use a minimum of 10 gal/acre for aerial applications. | ||||
| F. | POLYOXIN-D | |||
| (Oso) | 3.75-13 fl oz | 4 | 0 | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): chitin synthase inhibitor (19). | ||||
| COMMENTS: Apply in a 7- to 14-day interval. Do not apply more than 4.2 oz a.i. per season or no more than six applications per year. Do not make more than two sequential applications before rotating to non-chitin synthease inhibitor. Should be applied by ground using a sufficient amount of water to provide thorough coverage. | ||||
| ‡ | Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) 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. 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. |