UC IPM: UC Management Guidelines for Brown Rot on Fruit on Prune

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 6/06)

In this Guideline:

Symptoms
Comments on the disease
Management

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.

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.

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 (100KB, PDF).

Common name

Amount to Use

P.H.I.+

(trade name)

(days)

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.

PREHARVEST

PYRACLOSTROBIN/BOSCALID

(Pristine)

10.5–14.5 oz/acre

MODE OF ACTION: A Qol (Group 11)¹ and carboxamide (Group 7)¹ fungicide.

THIOPHANATE METHYL

(Topsin-M) 70WP

8 oz/100 gal water

MODE OF ACTION: A MBC (Group 1)¹ thiophanate fungicide.

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.

FENHEXAMID

(Elevate)

1–1.5 lb/acre

MODE OF ACTION: A hydroxyanilide (Group 17)¹ fungicide.

COMMENTS: Apply when conditions favor disease development. Do not apply more than 6 lb/acre/season.

MYCLOBUTANIL

(Rally) 40W

2.5–6 oz

MODE OF ACTION: A DMI (Group 3)¹ triazole fungicide.

COMMENTS: Do not apply more than 2.75 lb/acre/season.

POSTHARVEST

FLUDIOXONIL

(Scholar) 50WP

8 oz/100 gal water

MODE OF ACTION: A PP (Group 12)¹ fungicide.

COMMENTS: Treats 200,000 lb fruit using a spray-application system.

THIOPHANATE-METHYL

(Topsin-M) 70W

8 oz/100 gal water

MODE OF ACTION: A MBC (Group 1)¹ thiophanate fungicide.

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.

+	P.H.I. = Preharvest interval. Do not apply within this many days of harvest.
¹	Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of actions. Fungicides with a different Group number are suitable to alternate in a resistance management program. For more information, see http://www.frac.info/.

More information on prune fungicides

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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
F. J. A. Niederholzer, UC Cooperative Extension, 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 the diseases section:
B. L. Teviotdale, Kearney Agricultural Center, Parlier

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How to Manage Pests

UC Pest Management Guidelines

Prune

Brown Rot on Fruit

Pathogens: mostly Monilinia fructicola and M. laxa

SYMPTOMS

COMMENTS ON THE DISEASE

MANAGEMENT

More information on prune fungicides

PUBLICATION