How to Manage Pests

UC Pest Management Guidelines

Citrus

Brown Rot

Pathogen: Phytophthora spp.

(Reviewed 9/08, updated 4/14)

In this Guideline:


Symptoms

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

Comments on the Disease

Brown rot is caused by 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

Grove Management

Brown rot management primarily 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. In addition to copper, other products effective against brown rot include the phosphonate and phenylamide fungicides. Phosphonates are applied as foliar and fruit or soil treatments, whereas phenylamides are applied as soil treatments for brown rot control. For soil applications, microsprinkler irrigation applications may be used.

Postharvest Packinghouse Treatments to Prevent Fruit Decay

Potassium phosphite fungicides may be applied in aqueous dilutions to fruit alone or in combination with other postharvest fungicide treatments to manage nonvisible infections that occurred before harvest or protect fruit from brown rot infection after harvest during storage, distribution, and marketing. Use high-volume flooder or dip treatments for maximum coverage of fruit. Heated (125–136°F) fungicide solutions optimize performance of the potassium phosphite treatment.

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.
 
PREHARVEST
 
A. FIXED COPPER# Label rates See label 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 to 1 lb of hydrated lime per pound 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 to 1 lb of hydrated lime per pound 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 WDG) 5 lb/acre 12 30
  MODE-OF-ACTION GROUP NAME (FRAC NUMBER1): Phosphonate (33)
  COMMENTS: For use on all susceptible citrus. Apply in 500 gal/acre; spray to wet when conditions favor disease development. Do not exceed four applications of this product per year.
 
E. POTASSIUM PHOSPHITE
  (Fungi–Phite) 2 qt/acre 4 0
  MODE-OF-ACTION GROUP NAME (FRAC NUMBER1): Phosphonate (33)
  COMMENTS: For use on all susceptible citrus. Apply in 100 to 250 gal/acre; spray to wetness when conditions favor disease development. Do not exceed four applications of this product per year.
 
F. MEFENOXAM
  (Ridomil Gold) 1–3 qt/acre 48
  (Ridomil Gold) soil drench: 1–1.5 fl oz/100 gal water 48
  MODE-OF-ACTION GROUP NAME (FRAC NUMBER1): Phenylamides (4)
  COMMENTS: For use on all susceptible citrus. Apply to soil beneath the tree or through irrigation (i.e., chemigation) to reduce inoculum on roots and prevent high inoculum levels that are then splashed on to fruit during rain or irrigation periods. Make applications before flushes of root growth or twice a growing season. Apply March through April followed by one or two applications at three-month intervals to coincide with root flushes; rate depends on tree size and the number of applications per year. Apply 0.5 to 1 inch water after application. As a drench, apply 5 gallons around tree base within the watering ring. As a soil surface spray, spray the soil surface beneath the tree canopy and use sufficient water to obtain coverage of the soil surface wetted by irrigation. Follow immediately with irrigation sufficient to wet the soil 1 foot deep.
 
POSTHARVEST
 
A. POTASSIUM PHOSPHITE 4 pt/acre 4 0
  (Prophyt)
  MODE-OF-ACTION GROUP NAME (FRAC NUMBER1): Phosphonate (33)
  COMMENTS: For use on all susceptible citrus. Apply aqueous dilutions to fruit alone or in combination with other postharvest fungicide treatments to prevent brown rot decay in storage. Use high-volume flooder or dip treatments for maximum coverage of fruit. Heated (125–136°F) fungicide solutions optimize performance of the potassium phosphite treatment. After treatment, dry fruit on sponge and PVC rollers prior to fruit coating or wax applications. Do not apply potassium phosphite directly in fruit coatings or waxes.
 
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 R.E.I. exceeds the P.H.I. 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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