How to Manage Pests

UC Pest Management Guidelines

Citrus

Anthracnose

Pathogen: Colletotrichum gloeosporioides

(Reviewed 9/08, updated 9/08)

In this Guideline:


Symptoms

Symptoms of anthracnose on citrus include twig dieback, premature leaf drop, dark staining on fruit and postharvest fruit decay. Dying leaves and twigs become covered with dark fungal spores by which the pathogen spreads.

Anthracnose may blemish the rind tissue of mature Valencia and navel oranges, grapefruit, and occasionally lemon. The disorder affects mainly fruit on stressed trees with old, dead wood.

Comments on the Disease

The anthracnose fungus usually infects weakened twigs. The disease is most common during springs with prolonged wet periods and when significant rains occur later in the season than normal. During wet or foggy weather, anthracnose spores drip onto fruit, where they infect the rind and leave dull, reddish-to-green streaks on immature fruit and brown-to-black streaks on mature fruit (tear stains). Anthracnose tearstain often occurs with Septoria spot. The Septoria fungus itself and possibly certain environmental conditions may also cause tear staining. The stain cannot be washed off, but the disorder is generally not severe enough to require preventive actions. Certain conditions, however, such as applications of insecticidal soaps, which damage the protective wax on the fruit peel, can increase the severity of this disease.

Management

If treatment appears to be necessary, make applications in fall that are directed at the whole tree. Good coverage is important.

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. AZOXYSTROBIN
  (Abound) 2F 12–15.5 fl oz 4 0
  MODE OF ACTION GROUP NAME (FRAC NUMBER1): Quinone outside inhibitor (11)
 
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 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. 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.
 
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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