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UC Pest Management Guidelines


Powdery mildew on young peach fruit.

Nectarine

Powdery Mildew

Pathogen: Sphaerotheca pannosa and Podosphaera leucotricha

(Reviewed 6/10, updated 6/10)

In this Guideline:


SYMPTOMS AND SIGNS

Symptoms of powdery mildew can be seen on the terminal leaves of shoots, which are covered in powdery, white fungal growth. Leaves become misshapen and puckered, and fruits develop powdery, white spots that cause scars on mature fruit.

COMMENTS ON THE DISEASE

Sphaerotheca pannosa survives as mycelium in bud scales and as cleistothecia. Growth of the pathogen is favored by cool, moist nights and warm days. Generally, fruit is susceptible only up to time of pit hardening, but later infections can occur. Certain cultivars are more susceptible.

Occasionally the apple powdery mildew fungus, Podosphaera leucotricha, will attack nectarine fruit. Inoculum is produced only in apple orchards.

MANAGEMENT

Management of powdery mildew on nectarines focuses on protecting fruit from infections. Watch for the disease during routine monitoring. Avoid growing nectarines near apple varieties that are highly susceptible to powdery mildew, such as Jonathan, Gravenstein, and Rome Beauty. If nearby apples are expected to cause mildew problems on nectarines, control the disease on apples or apply a fungicide to nectarines at jacket split.

Organically Acceptable Methods
Sulfur sprays are acceptable for use in an organically certified crop.

Chemical Control
Apply one of the fungicides listed below from bloom until pit hardening or later when necessary. Up to three applications may be necessary in seasons when nights are cool and moist and daytime temperatures are warm. Early treatments are the most important and most effective. It is important to alternate materials of a different chemistry to prevent the development of resistance to a fungicide.

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. MYCLOBUTANIL
  (Rally 40W) 2.5–6 oz/acre 24 0
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
 
B. QUINOXYFEN
  (Quintec) 7 fl oz/acre 12 7
  MODE OF ACTION GROUP NAME (NUMBER1): Quinoline (13)
  COMMENTS: Use allowed under a Supplemental Label. Re-treat at 10 to 14 day interval if necessary.
 
C. SULFUR DUST# 50 lb/acre see label see label
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M2)
  COMMENTS: Do not apply within 3 weeks of an oil application.
 
D. WETTABLE SULFUR# 5–10 lb/100 gal water see label see label
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M2)
  COMMENTS: Do not apply within 3 weeks of an oil application.
 
E. WETTABLE SULFUR#
  . . . PLUS . . .
  LIQUID LIME SULFUR# Label rates see label see label
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M2)
  COMMENTS: Do not apply within 3 weeks of an oil application.
 
F. 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)
 
G. 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.
 
H. PROPICONAZOLE
  (Bumper, Tilt) 4 oz/acre Tilt: 12
Bumper: 24
0
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
 
I. 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.
 
J. METCONAZOLE
  (Quash) 3.5–4 oz/acre 12 14
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
  COMMENTS: Do not make more than 3 applications/season.
 
K. 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.
 
L. THIOPHANATE METHYL
  (Topsin-M 70WP) 8 oz/100 gal water 12 1
  MODE OF ACTION GROUP NAME (NUMBER1): Methyl benzimidazole (1)
 
+ 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.
# Acceptable for use on organically grown produce.
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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