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UC Pest Management Guidelines


Scab lesions on peach fruit.

Nectarine

Scab

Pathogen: Cladosporium carpophilum

(Reviewed 6/10, updated 6/10)

In this Guideline:


SYMPTOMS AND SIGNS

Scab affects foliage, young shoots, and fruit, but damage is the result of fruit infections. Fruit infections appear as dark lesions on ripening fruit, most commonly on the upper surface, and may grow together to form large blotches. Lesions may have green or yellowish blotches that turn grayish when spores are produced.

COMMENTS ON THE DISEASE

Primarily a problem on nectarines in the northern San Joaquin Valley during wet spring weather. The fungus that causes scab overwinters in lesions on first-year twigs. Spores are produce in these lesions when humidity exceeds 70% beginning at bloom and lasting several weeks. Spores are spread by air movement and splashing water and will infect developing fruit, although it may take several weeks for lesions to appear.

MANAGEMENT

In orchards with a history of scab, applications of a fungicide within 3 weeks after full bloom, and again at 5 weeks if disease was severe the previous year, will reduce fruit infection. Fungicides applied during bloom for brown rot and at petal fall to control shot hole will also reduce the spread of scab if appropriate fungicides are chosen.

Take a fruit damage sample at harvest to assess the effectiveness of the current year's IPM program and to determine the needs of next year's program, see FRUIT EVALUATION AT HARVEST. Record results (115 KB, PDF) for harvest sample.

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. TRIFLOXYSTROBIN
  (Gem) 3.8 oz 12 1
  MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
 
B. AZOXYSTROBIN
  (Abound) 12.3–15.4 fl oz/acre 4 0
  MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
  COMMENTS: Do not apply more than two applications before alternating with a fungicide that has a different mode of action group number.
 
C. 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.
 
D. PYRACLOSTROBIN/BOSCALID
  (Pristine) 10.5–14.5 oz/acre 12 0
  MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) and Carboxamide (7)
  COMMENTS: To reduce the potential for resistance, do not make more than 5 applications of this or other Group 11 or 7 fungicides per season. Do not make more than 2 sequential applications of this product.
 
E. CHLOROTHALONIL
  (Echo 720) 3.125–4.125 pt/acre 12 see comments
  (Bravo Ultrex DF) 2.8-3.8 lb/acre 12 0
  (Bravo Weather Stik) 3.125–4.125 pt/acre 12 0
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M5)
  COMMENTS: Do not use with or closely following oil sprays. Do not apply Echo 720 after shuck split.
 
F. THIOPHANATE METHYL
  (Topsin-M, etc. 70WP) 8 oz/100 gal water 12 1
  MODE OF ACTION GROUP NAME (NUMBER1): Methyl benzimidazole (1)
 
G. CAPTAN 50WP
  (various products) 2 lb/100 gal water (dilute spray) 24 0
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M4)
  COMMENTS: Do not apply in combination with, immediately before, or closely following oil sprays.
 
H. ZIRAM 76DF 2–2.5 lb/100 gal water (dilute spray) 48 30
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M3)
 
+ 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.

IMPORTANT LINKS

[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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