How to Manage Pests

UC Pest Management Guidelines

Citrus

Brown Rot

Pathogen: Phytophthora spp.

(Reviewed 9/08, updated 9/08)

In this Guideline:


Symptoms

Symptoms appear primarily on mature or nearly mature fruit. Initially, the firm, leathery lesions have a water-soaked appearance, but they soon turn soft and have a tan to olive brown color and a pungent odor. Infected fruit eventually drop. Occasionally, twigs, leaves, and blossoms are infected, turning brown and dying.

Comments on the Disease

Brown rot is caused multiple species of Phytophthora when conditions are cool and wet. Brown rot develops mainly on fruit growing near the ground when Phytophthora spores from the soil are splashed onto the tree skirts during rainstorms; infections develop under continued wet conditions. Fruit in the early stage of the disease may go unnoticed at harvest and infect other fruit during storage.

Management

Brown rot management relies on prevention. Pruning tree skirts 24 or more inches above the ground can significantly reduce brown rot.

One spray of copper fungicide between October and December before or just after the first rain may provide protection throughout the wet season. When rainfall is excessive, you may have to repeat the spray in January or February. Spray the skirts to about 4 feet above ground. Spraying the ground underneath the trees also reduces brown rot infections.

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# Label rates 24 0
  MODE OF ACTION GROUP NAME (FRAC NUMBER1): Multi-site contact (M1)
  COMMENTS: Where danger of copper injury is severe, apply in a mixture with 0.33–1 lb of hydrated lime per lb of dry copper fungicide. Not all copper compounds are approved for use in organic production; be sure to check individual products.
 
B. ZINC SULFATE+COPPER SULFATE+HYDRATED LIME#
  (3-2-6-100) 10–24 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. Mix in 100 gal water. Apply from October through December, or just before or after first rain. Conveniently packaged, neutral copper zinc spray-dried materials to give equivalent metal content (0.6–0.8lb of metallic copper/100 gal water) may also be used if 4 oz of casein spreader-sticker are added per 100 gal water. More concentrated formulations of some materials may be applied at low volumes. Where danger of copper injury is severe, these products may be modified to make them safer by adding 0.33–1 lb of hydrated lime per/lb of dry copper fungicide. 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.
 
C. BORDEAUX# (3-4.5-100) 10–24 gal/tree See comments See comments
  MODE OF ACTION GROUP NAME (FRAC NUMBER1): Multi-site contact (M1)
  COMMENTS: For use on lemons, oranges, and grapefruit where there is no history of copper injury. Mix in 100 gal water. Not all copper compounds are approved for use in organic production; be sure to check individual products. For information on making Bordeaux mixture, see UC IPM Pest Note: Bordeaux Mixture,. 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. Use the restricted entry interval and preharvest interval of the product with the most restrictive label of those used in the tank mix.
 
D. FOSETYL-AL
  (Aliette) 80WDG 5 lb/acre 12 30
  MODE OF ACTION GROUP NAME (FRAC NUMBER1): Phosphonate (33)
  COMMENTS: For use on all susceptible citrus. Apply in 100 gal/acre; spray to wet when conditions favor disease development. Do not exceed 4 applications of this product per year.
 
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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