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How to Manage Pests

UC Pest Management Guidelines

| More pests | More crops | About guidelines |

Young fruit killed by Botrytis rot.

Citrus

Botrytis Diseases And Disorders

Pathogen: Botrytis cinerea

(Reviewed 9/08, updated 9/08)

In this Guideline:

SYMPTOMS

The Botrytis pathogen commonly infects tissue through injuries and forms gray, velvety mats of sporulating tissues. Infected twigs may die back several inches. Infected blossoms often result in increased fruit drop and in injuries to the developing fruit. These fruit injuries are evident as ridges on mature fruit that result in a lower graded crop during marketing. The name "gray mold" is used to describe the disease when it occurs as fruit decay during postharvest storage.

COMMENTS ON THE DISEASE

Botrytis cinerea is a ubiquitous fungus that causes disease on twigs, leaves, blossoms, and fruit of citrus in areas with prolonged wet and cool conditions. Generally, the organism is a minor pathogen of citrus; lemons are infected more commonly than other citrus crops.

MANAGEMENT

General preventive measures, such as avoiding mechanical injury, protecting against frost and brown rot, and pruning regularly to improve air movement may help reduce the incidence of Botrytis diseases. Treatments with copper and benzimidazole fungicides before rain or fog may help to reduce the blossom and fruit phases of the disease. Under prolonged cool, wet environmental conditions, frequent treatments are required and these may not be economical. Postharvest treatments may be required in wet years to prevent fruit decay during storage and marketing.

Common name Amount to Use R.E.I.+ P.H.I.+
(trade name)   (hours) (days)
When choosing a pesticide, consider the general properties of the fungicide as well as information relating to environmental impact.
 
PREHARVEST (BLOSSOM AND FRUIT INJURIES)
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.
 
POSTHARVEST (GRAY MOLD FRUIT DECAY)
A. FLUDIOXONIL
  (Graduate) 16-32 oz NA NA
  MODE OF ACTION GROUP NAME (FRAC NUMBER1): Phenylpyrrole (12)
  COMMENTS: Use as a dip, drench, flood, or spray. See label for dilution rates. For maximum control, treat once before and once after storage; do not make more than two applications.
 
B. PYRIMETHANIL
  (Penbotec) 400SC Label rates NA NA
  MODE OF ACTION GROUP NAME (FRAC NUMBER1): Anilinopyrimidine (9)
 
+ 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.
NA Not applicable.

IMPORTANT LINKS

[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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Statewide IPM Program, Agriculture and Natural Resources, University of California
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