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Peach shoot and fruit killed by brown rot fungus.

Nectarine

Brown Rot Blossom and Twig Blight

Pathogens: Monilinia fructicola, occasionally Monilinia laxa

(Reviewed 6/10, updated 6/10)

In this Guideline:


SYMPTOMS AND SIGNS

Young blossom spurs and associated leaves collapse to form shoot blight. Gum exudes at base of infected flowers. Cankers on blighted twigs have tan centers with dark margins. Gray brown spore masses form on diseased flower parts and twig cankers under high humidity.

Monilinia fructicola overwinters on mummified fruit that either fall to the ground in late fall or early winter, or remain in the trees. In spring, apothecia form on mummies that are on the ground; these apothecia release ascospores at the same time as the trees bloom. Ascospores serve as primary inoculum for brown rot in many orchards. Mummies in the trees as well as those on the ground may also produce conidia, which may serve as the primary source of inoculum in some years. Twig lesions apparently do not produce spores.

COMMENTS ON THE DISEASE

Although all flower parts except the sepals are susceptible to infection by M. fructicola, only infection of the stamens leads to the development of blossom and twig blight.

MANAGEMENT

Bloom sprays to reduce blossom and twig blight help minimize loss to ripe fruit rot at harvest. Removal of fruit remaining on trees soon after harvest and before they become mummies may help prevent reinfection of blossoms the following bloom.

Chemical Control
Make a treatment at 20 to 40% bloom and again at 80 to 100% bloom on susceptible varieties or if heavy rainfall and other conditions are occurring that result in high susceptibility to infection. Early season varieties, especially the low-chilling ones, only need a single spray.

Aerial applications are generally not as effective as properly applied ground sprays but may be necessary when the orchard floor is wet. To help recduce development of resistance to fungicides, be sure to rotate chemicals that have different mode of action Group numbers.

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.
 
A. TEBUCONAZOLE/TRIFLOXYSTROBIN
  (Adament 50 WG ) 4–8 oz/acre 5 days 1
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3) and Quinone outside inhibitor (11)
 
B. PROPICONAZOLE
  (Bumper, Tilt) 4 oz/acre Tilt: 12
Bumper: 24
0
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
 
C. TEBUCONAZOLE
  (Elite, etc. 45WP) 4–8 oz/acre 12 0
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
  COMMENTS: Do not apply more than 3 lb/acre/season.
 
D. FENBUCONAZOLE
  (Indar 75WSP) 2 oz/acre 12 0
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
  COMMENTS: Do not apply more than 1 lb/acre/season.
 
E. IPRODIONE
  (Rovral 4) 1–2 pt/acre 24 see comments
  MODE OF ACTION GROUP NAME (NUMBER1): Dicarboximide (2)
  COMMENTS: Addition of a narrow range oil (superior, supreme) at 1–2% increases the effectiveness of this material. May not be used after petal fall.
 
F. METCONAZOLE
  (Quash) 2.5–3.5 oz/acre 12 14
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
  COMMENTS: Do not make more than 3 applications/season.
 
G. PYRACLOSTROBIN/BOSCALID
  (Pristine) 10.5–14.5 oz/acre 12 0
  MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) and Carboxamide (7)
 
H. THIOPHANATE METHYL
  (Topsin-M, etc. 70WP) 8 oz/100 gal water 12 1
  MODE OF ACTION GROUP NAME (NUMBER1): Methyl benzimidazole (1)
  COMMENTS: Strains of Monilinia fructicola resistant to thiophanate methyl are common, especially in the Sacramento and northern San Joaquin Valleys. If resistance has occurred in your orchard, do not use this fungicide; otherwise, one application at early bloom is usually sufficient. If brown rot is severe, or an extended bloom period is accompanied by rainfall, make a second application using a fungicide with a different group number.
 
I. CYPRODINIL
  (Vangard WG) 5 oz/acre 12 2
  MODE OF ACTION GROUP NAME (NUMBER1): Anilinopyrimidine (9)
  COMMENTS: Do not apply more than 10 oz/acre/year.
 
J. PYRIMETHANIL
  (Scala SC) 18 fl oz 12 2
  MODE OF ACTION GROUP NAME (NUMBER1): Anilinopyrimidine (9)
 
K. FENHEXAMID
  (Elevate 50 WDG) 1–1.5 lb/acre 12 0
  MODE OF ACTION GROUP NAME (NUMBER1): Hydroxyanilide (17)
 
L. MYCLOBUTANIL
  (Rally 40W) 2.5–6 oz/acre 24 0
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
  COMMENTS: Do not apply more than 3.25 lb/acre/season.
 
+ 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 a fungicide with a different mode of action Group number.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Nectarine
UC ANR Publication 3451
Diseases
J. E. Adaskaveg, Plant Pathology, UC Riverside
R. A. Duncan, UC Cooperative Extension Stanislaus County
K. R. Day, UC Cooperative Extension, Tulare County
Acknowledgment for contributions to Diseases:
B. L. Teviotdale, Kearney Agricultural Center, Parlier
W. D. Gubler, Plant Pathology, UC Davis

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