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UC Pest Management Guidelines


Sporulation on the surface of a fruit infected with Monilinia fructicola.

Prune

Brown Rot on Fruit

Pathogens: mostly Monilinia fructicola and M. laxa

(Reviewed 6/06, updated 4/09)

In this Guideline:


SYMPTOMS AND SIGNS

Fruit with brown rot infections are shriveled and develop powdery tan masses of spores. Individual fruit may be infected, but rotted fruit usually occur in clusters that are stuck together.

COMMENTS ON THE DISEASE

Injured fruit and fruit that touch each other are the most susceptible to brown rot infections. Most clustered, rotted fruit are separated from healthy fruit during harvest operations. The drying process protects fruit from further postharvest rots.

MANAGEMENT

Removing or turning under thinned fruit helps reduce fruit brown rot. Thinned fruit can be a source of inoculum for brown rot on ripening fruit, especially if they are left where they will come in contact with irrigation water. Unlike brown rot on peach and nectarine, control of brown rot blossom and twig blight (spring brown rot) of prune does not appear to have any effect on harvest levels of brown rot on fruit.

Fungicides are preventive, not eradicative; they must be applied to uninjured fruit before infections occur. Injured fruit cannot be protected from rot caused by Monilinia with the use of preharvest sprays. Apply preharvest sprays as needed 4 to 6 weeks before harvest.

Fruit damage sample. In mid-July, take a fruit damage sample to assess the overall effectiveness of the current year's IPM program and to determine next year's needs. For details, see FRUIT EVALUATION AT HARVEST. Record results on a monitoring form (84 KB, PDF).

Common name Amount to Use R.E.I.+ P.H.I.+
(trade name)   (hours) (days)

  Calculate impact of pesticide on air quality
The following materials are listed in order of usefulness in an IPM program, taking into account efficacy. When choosing a pesticide, also consider information relating to environmental impact. Not all registered pesticides are listed. Always read label of product being used.
 
PREHARVEST
A. PYRACLOSTROBIN/BOSCALID
  (Pristine) 10.5–14.5 oz/acre 12 0
  MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) and Carboxamide (7)
 
B. THIOPHANATE METHYL
  (Topsin-M) 70WP 8 oz/100 gal water 12 1
  MODE OF ACTION GROUP NAME (NUMBER1): Methyl benzimidazole (1)
  COMMENTS: Addition of a narrow range oil (superior, supreme) at 1–2% increases the effectiveness of this material and will aid in aphid control. Strains of Monilinia fructicola resistant to thiophanate methyl have been found in California. If resistance has occurred in your orchard, do not use this fungicide. Use only 1 application of thiophanate methyl/year, and always apply with a fungicide of different chemistry.
 
C. FENHEXAMID
  (Elevate) 1–1.5 lb/acre 12 0
  MODE OF ACTION GROUP NAME (NUMBER1): Hydroxyanilide (17)
  COMMENTS: Apply when conditions favor disease development. Do not apply more than 6 lb/acre/season.
 
D. MYCLOBUTANIL
  (Rally) 40W 2.5–6 oz 24 0
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
  COMMENTS: Do not apply more than 2.75 lb/acre/season.
 
POSTHARVEST
A. FLUDIOXONIL
  (Scholar) 50WP 8 oz/100 gal water NA NA
  MODE OF ACTION GROUP NAME (NUMBER1): Phenylpyrrole (12)
  COMMENTS: Treats 200,000 lb fruit using a spray-application system.
 
B. THIOPHANATE METHYL
  (Topsin-M) 70W 8 oz/100 gal water NA NA
  MODE OF ACTION GROUP NAME (NUMBER1): Methyl benzimidazole (1)
  COMMENT: Sporadic control may occur if fruit treated is infected with spores of benzimidazole-resistant strains of Monilinia spp. If resistance has occurred in your orchard, do not use this fungicide.
 
+ 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.
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: Prune
UC ANR Publication 3464
Diseases
W. D. Gubler, Plant Pathology, UC Davis
J. E. Adaskaveg, Plant Pathology, UC Riverside
C. Pickel, UC IPM Program, Sutter/Yuba counties
W. H. Olson, UC Cooperative Extension, Butte County
F. J. A. Niederholzer, UC Cooperative Extension, Sutter/Yuba counties
Acknowledgment for contributions to Diseases:
B. L. Teviotdale, Kearney Agricultural Center, Parlier

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