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UC Pest Management Guidelines


Russet scab on developing prunes.

Prune

Russet Scab

(Reviewed 6/06, updated 4/09)

In this Guideline:


SYMPTOMS AND SIGNS

Russet scab, also known as lacey scab, is a physiological disorder that causes a superficial russeting of fruit; most prevalent on stylar end.

COMMENTS ON THE DISEASE

Russet scab develops in years of excessive rain during and soon after bloom. Research has shown that prunes with 75% scab are not contributing to off grade.

MANAGEMENT

Treat just before or at full bloom in fresh market prunes.

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. CAPTAN 50WP 6 lb 4 days 0
  (various products)
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M4)
  COMMENTS: Do not apply in combination with, immediately before, or closely following oil sprays.
 
B. CHLOROTHALONIL
  (Bravo Weather Stik) 3.125–5.5 pt 12 0
  (Echo 720) 3.125–4.125 pt 12 0
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M5)
  COMMENTS: Use higher rate on trees taller than 20 ft and lower rate on smaller trees. Do not use with or closely following oil sprays.
 
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.
+ 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.

[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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