How to Manage Pests

UC Pest Management Guidelines

Peach

Powdery Mildew

Pathogens: Sphaerotheca pannosa and Podosphaera leucotricha

(Reviewed 4/10, updated 4/10, pesticides updated 9/15)

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 can scar over as the fruit mature.

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 peach fruit. Inoculum is produced only in apple orchards.

MANAGEMENT

Management of powdery mildew on peaches focuses on protecting fruit from infections. Watch for the disease during routine monitoring. Avoid growing peaches 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 peaches, control the disease on apples or apply a fungicide to peaches 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. It is important to alternate materials of a different chemistry to prevent the development of resistance to a fungicide. Early treatments are the most important and most effective.

Common name Amount per acre REI‡ PHI‡
(Example trade name)   (hours) (days)

UPDATED: 9/15
Calculate impact of pesticide on air quality
When choosing a pesticide, consider its usefulness in an IPM program by reviewing the pesticide's properties, efficacy, application timing, and information relating to resistance management, honey bees, and environmental impact. Not all registered pesticides are listed. Always read the label of the product being used.
 
A. MYCLOBUTANIL
  (Rally 40WSP) 2.5–6 oz 24 0
  MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
 
B. QUINOXYFEN
  (Quintec) 7 fl oz 12 7
  MODE-OF-ACTION GROUP NAME (NUMBER1): Quinoline (13)
  COMMENTS: Re-treat at 10 to 14 day interval if necessary.
 
C. SULFUR DUST# 50 lb 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
  (Adamant 50WG) 4–8 oz 5 days 1
  MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3) and Quinone outside inhibitor (11)
 
G. TEBUCONAZOLE
  (Elite, 45WP) 4–8 oz 120 (5 days) 0
  MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
  COMMENTS: Do not apply more than 3 lb/acre per season.
 
H. PROPICONAZOLE
  (Bumper, Tilt) 4 fl oz 12 0
  MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
 
I. FENBUCONAZOLE
  (Indar 2F) 6 fl oz 12 0
  MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
  COMMENTS: Do not apply more than 1 lb/acre per season.
 
J. METCONAZOLE
  (Quash) 3.5–4 oz 12 14
  MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
  COMMENTS: Do not make more than 3 applications per season.
 
K. PYRACLOSTROBIN+BOSCALID
  (Pristine) 10.5–14.5 oz 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) 1 1/2 lb/acre 12 1
  MODE-OF-ACTION GROUP NAME (NUMBER1): Methyl benzimidazole (1)
 
Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) 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: Peach
UC ANR Publication 3454

Diseases

J. E. Adaskaveg, Plant Pathology, UC Riverside
R. A. Duncan, UC Cooperative Extension Stanislaus County
J. K. Hasey, UC Cooperative Extension Sutter/Yuba counties
K. R. Day, UC Cooperative Extension Tulare County

Acknowledgment for contributions to Diseases:
W. D. Gubler, Plant Pathology, UC Davis
B. L. Teviotdale, Kearney Agricultural Center, Parlier

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