Agriculture: Almond Pest Management Guidelines

Scab

  • Fusicladium carpophilum
  • Symptoms and Signs

    Grayish black, soft looking spots form on leaves, fruit, and twigs. Young lesions are indistinct small yellow specks, best seen by holding a leaf up to the light. Lesions usually are not visible until late spring or early summer.

    Comments on the Disease

    The fungus survives in twig lesions, and spores are spread by wind or rain. The disease is favored by prolonged wet spring weather, and is most prevalent in the Sacramento Valley. Severe scab infections cause early defoliation; if left uncontrolled for several years, infected trees will become weakened. The disease often occurs in sprinkler-irrigated orchards where water reaches foliage.

    Management

    To determine if a fungicide application is warranted, follow the sampling and treatment threshold guidelines in the section DORMANT SPUR SAMPLING. Record observations in a sampling form (PDF).

    Scab may be controlled by shot hole fungicide sprays. However, a scab treatment may be required if rain occurs into mid- to late spring. One application as late as 5 weeks after petal fall can protect against scab, but an earlier application (2 weeks after petal fall) may improve control.

    In severe outbreaks, dormant or delayed dormant applications of copper with oil or liquid lime sulfur can be used effectively to reduce and delay sporulation of twig infections in spring. Copper and oil has been found to be the most effective delayed dormant treatment, and when used in combination with petal fall applications of protective fungicides, the disease can be effectively managed.

    Scab resistance to quinone outside inhibitor fungicides (also known as strobilurins) has been documented; do not use FRAC mode-of-action group number 11 fungicides in these orchards.

    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.
    DORMANT
    A. LIME SULFUR#
    (various) Label rates See label See label
    MODE-OF-ACTION GROUP NAME (NUMBER1): Multi-site contact (M2)
    COMMENTS: Can improve spring control of scab, especially if a wet spring delays treatment. Check with your certifier to determine which products are organically acceptable.
    B. COPPER
    (various) Label rates See label See label
    MODE-OF-ACTION GROUP NAME (NUMBER1): Multi-site contact (M1)
    . . . PLUS . . .
    NARROW RANGE OIL#
    (various) Label rates See label See label
    MODE-OF-ACTION: Contact
    COMMENTS: Not all copper and oil products are organically acceptable; check with your certifier.
    C. CHLOROTHALONIL
    (Bravo Weather Stik) Label rates See label See label
    MODE-OF-ACTION GROUP NAME (NUMBER1): Multi-site contact (M1)
    . . . PLUS . . .
    NARROW RANGE OIL#
    (various) Label rates See label See label
    MODE-OF-ACTION: Contact
    COMMENTS: Apply as dormant or delayed dormant treatment. Do not apply within two weeks of bud swell.
    PETAL FALL (beginning of sporulation of twig infections)
    A. FLUOPYRAM/TRIFLOXYSTROBIN
    (Luna Sensation) 5.0-7.6 fl oz 12 14
    MODE-OF-ACTION GROUP NAME (NUMBER1): succinate dehydrogenase inhibitor (7) and Quinone outside inhibitor (11)
    COMMENTS: Do not make more than two successive applications, and no more than four per season, to limit the development of resistance.
    B. AZOXYSTROBIN/PROPICONAZOLE
    (Quilt Xcel) 17.5-26.0 fl oz 12 60
    MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) and demethylation (sterol) inhibitor (3)
    COMMENTS: Do not make more than two successive applications, and no more than four per season, to limit the development of resistance.
    C. PYRACLOSTROBIN/FLUXAPYROXAD
    (Merivon) 5–6.5 fl oz 12 14
    MODE-OF-ACTION GROUP NAME (NUMBER1): quinone outside inhibitor (11) and succinate dehydrogenase inhibitor (7)
    COMMENTS: Do not make more than three applications per season of Merivon to limit the potential for the development of resistance.
    D. PYRACLOSTROBIN/BOSCALID
    (Pristine) 10.5–14.5 oz 12 25
    MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) and succinate dehydrogenase inhibitor (7)
    COMMENTS: Do not make more than four applications per season of QoIs or succinate dehydrogenase inhibitor and no more than two sequential applications before rotation to a different mode of action fungicide to limit the potential for the development of resistance.
    E. AZOXYSTROBIN
    (Abound) 12.0–15.5 oz 4 28
    MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
    COMMENTS: Do not apply more than two sequential sprays before alternating with a fungicide that has a different mode of action. Do not apply more than four applications of strobilurin fungicides per year or apply more than 92.3 fl oz/acre per season.
    F. TRIFLOXYSTROBIN
    (Gem 500SC) 3.8 oz 12 14
    MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
    COMMENTS: Do not apply within 14 days of harvest or after hullsplit. Do not make more than four applications per season and no more than two sequential sprays of QoI or SDHI fungicides to limit the potential for the development of resistance.
    G. METCONAZOLE
    (Quash) 3.0 oz 12 25
    MODE-OF-ACTION GROUP NAME (NUMBER1): demethylation (sterol) inhibitor (3)
    COMMENTS: Do not make more than two successive applications and no more than four per season to limit the development of resistance. Do not apply after hullsplit.
    H. AZOXYSTROBIN/DIFENOCONAZOLE
    (Quadris Top) 14 oz 12 28
    MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) and demethylation (sterol) inhibitor (3)
    COMMENTS: Do not make more than two successive applications, and no more than four per season, to limit the development of resistance.
    I. THIOPHANATE-METHYL
    (Topsin M 70WSB) 1.5 lb 72 (3 days) See label
    MODE-OF-ACTION GROUP NAME (NUMBER1): Methyl benzimidazole (1)
    COMMENTS: Strains of scab pathogen resistant to thiophanate-methyl may occur. Do not apply more than once a year.
    J. CHLOROTHALONIL
    (Bravo Weather Stik, Echo 720) Label rates See label See label
    MODE-OF-ACTION GROUP NAME (NUMBER1): Multi-site contact (M5)
    COMMENTS: Do not apply one week before or after a treatment containing oil or an oil-based pesticide.
    K. ZIRAM
    (Ziram 76DF) 8 lb 48 0
    MODE-OF-ACTION GROUP NAME (NUMBER1): Multi-site contact (M3)
    COMMENTS: Do not apply more than 32 lb/acre per season. Do not apply later than 5 weeks after petal fall.
    L. CAPTAN
    (various 50WP) Label rates See label See label
    MODE-OF-ACTION GROUP NAME (NUMBER1): Multi-site contact (M4)
    COMMENTS: Do not apply in combination with, immediately before, or closely following oil sprays.
    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 these two intervals is the minimum time that must elapse before harvest may occur.
    # Acceptable for use on organically grown produce.
    1 Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of action. 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: 08/17
    Treatment Table Updated: 08/17