Agriculture: Nectarine Pest Management Guidelines

Brown Rot Blossom and Twig Blight

  • Monilinia fructicola, occasionally Monilinia laxa
  • Symptoms and Signs

    Young blossom spurs and associated leaves collapse to form shoot blight. Gum exudes at base of infected flowers. Cankers on blighted twigs have tan centers with dark margins. Gray brown spore masses form on diseased flower parts and twig cankers under high humidity.

    Monilinia fructicola overwinters on mummified fruit that either fall to the ground in late fall or early winter, or remain in the trees. In spring, apothecia form on mummies that are on the ground; these apothecia release ascospores at the same time as the trees bloom. Ascospores serve as primary inoculum for brown rot in many orchards. Mummies in the trees as well as those on the ground may also produce conidia, which may serve as the primary source of inoculum in some years. Twig lesions apparently do not produce spores.

    Comments on the Disease

    Although all flower parts except the sepals are susceptible to infection by M. fructicola, only infection of the stamens leads to the development of blossom and twig blight.

    Management

    Bloom sprays to reduce blossom and twig blight help minimize loss to ripe fruit rot at harvest. Removal of fruit remaining on trees soon after harvest and before they become mummies may help prevent reinfection of blossoms the following bloom.

    Chemical Control

    Make a treatment at 20 to 40% bloom and again at 80 to 100% bloom on susceptible varieties or if heavy rainfall and other conditions are occurring that result in high susceptibility to infection. Early season varieties, especially the low-chilling ones, only need a single spray.

    Aerial applications are generally not as effective as properly applied ground sprays but may be necessary when the orchard floor is wet. To help recduce development of resistance to fungicides, be sure to rotate chemicals that have different mode of action Group numbers.

    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. TEBUCONAZOLE+TRIFLOXYSTROBIN
      (Adament 50WG) 4–8 oz 5 days 1
      MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3) and Quinone outside inhibitor (11)
     
    B. PROPICONAZOLE
      (Bumper, Tilt) 4 oz 12 0
      MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
     
    C. TEBUCONAZOLE
      (Elite 45WP) 4–8 oz 5 days 0
      MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
      COMMENTS: Do not apply more than 3 lb/acre per season.
     
    D. FENBUCONAZOLE
      (Indar 2F) 6 oz 12 0
      MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
      COMMENTS: Do not apply more than 1 lb/acre per season.
     
    E. IPRODIONE
      (Rovral 4) 1–2 pt 24 See comments
      MODE-OF-ACTION GROUP NAME (NUMBER1): Dicarboximide (2)
      COMMENTS: Addition of a narrow range oil (superior, supreme) at 1–2% increases the effectiveness of this material. May not be used after petal fall.
     
    F. METCONAZOLE
      (Quash) 2.5–3.5 oz 12 14
      MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
      COMMENTS: Do not make more than 3 applications per season.
     
    G. PYRACLOSTROBIN+BOSCALID
      (Pristine) 10.5–14.5 oz 12 0
      MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) and Carboxamide (7)
     
    H. THIOPHANATE METHYL
      (Topsin-M 70WP) 1 1/2 lb 12 1
      MODE-OF-ACTION GROUP NAME (NUMBER1): Methyl benzimidazole (1)
      COMMENTS: Strains of Monilinia fructicola resistant to thiophanate methyl are common, especially in the Sacramento and northern San Joaquin Valleys. If resistance has occurred in your orchard, do not use this fungicide; otherwise, one application at early bloom is usually sufficient. If brown rot is severe, or an extended bloom period is accompanied by rainfall, make a second application using a fungicide with a different group number.
     
    I. CYPRODINIL
      (Vangard WG) 10 oz 12 2
      MODE-OF-ACTION GROUP NAME (NUMBER1): Anilinopyrimidine (9)
      COMMENTS: Do not apply more than 10 oz/acre per year.
     
    J. PYRIMETHANIL
      (Scala SC) 18 fl oz 12 2
      MODE-OF-ACTION GROUP NAME (NUMBER1): Anilinopyrimidine (9)
      COMMENTS: Do not apply within 2 days of fruit harvest or make more than 2 applications of a Group 9 fungicide within 30 days of harvest.
     
    K. FENHEXAMID
      (Elevate 50WDG) 1–1.5 lb 12 0
      MODE-OF-ACTION GROUP NAME (NUMBER1): Hydroxyanilide (17)
      COMMENTS: Do not apply more than 6 lb/acre per season and avoid making more than 2 consecutive applications with this material.
     
    L. MYCLOBUTANIL
      (Rally 40W) 2.5–6 oz 24 0
      MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
      COMMENTS: Do not apply more than 3.25 lb/acre per season.
    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.
    1 Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of actions. 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: 06/10
    Treatment Table Updated: 09/15