Agriculture: Peach Pest Management Guidelines

Powdery Mildew

  • Powdery mildew: Podosphaera leucotricha, Sphaerotheca pannosa
  • 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)
    Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least likely to cause resistance are at the top of the table. When choosing a pesticide, consider information relating to the pesticide's properties and application timing, honey bees, and environmental impact. 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.
    Text Updated: 09/15
    Treatment Table Updated: 09/15