Agriculture: Citrus Pest Management Guidelines

Anthracnose

  • Colletotrichum gloeosporioides
  • Symptoms and Signs

    Symptoms of anthracnose on citrus include twig dieback, premature leaf drop, dark staining on fruit and postharvest fruit decay. Dying leaves and twigs become covered with dark fungal spores by which the pathogen spreads.

    Anthracnose may blemish the rind tissue of mature Valencia and navel oranges, grapefruit, and occasionally lemon. The disorder affects mainly fruit on stressed trees with old, dead wood.

    Comments on the Disease

    The anthracnose fungus usually infects weakened twigs. The disease is most common during springs with prolonged wet periods and when significant rains occur later in the season than normal. During wet or foggy weather, anthracnose spores drip onto fruit, where they infect the rind and leave dull, reddish to green streaks on immature fruit and brown to black streaks on mature fruit (tear stains).

    Anthracnose tear stains often occur with Septoria spot. The Septoria fungus itself, and possibly certain environmental conditions, may also cause tear staining. The stain cannot be washed off, but the disorder is generally not severe enough to require preventive actions. Certain conditions, however, such as applications of insecticidal soaps, which damage the protective wax on the fruit peel, can increase the severity of this disease.

    Management

    If a fungicide application is necessary, make applications in the fall that are directed at the whole tree. Good coverage is important.

    Common name Amount to use 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‚Äôs properties and application timing, honey bees, and environmental impact. Always read the label of the product being used.
     
    A. AZOXYSTROBIN
      (Abound 2F) 12–15.5 fl oz 4 0
      MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
      COMMENTS: Apply in a 7- to 21-day interval. Do not apply more than 92.3 fl oz of product per season or 1.5 lb of azoxystrobin per crop. Do not make more than two sequential applications before rotating to a non-QoI group. May be applied by ground or by air. Use a sufficient amount of water to provide thorough coverage. Use a minimum of 10 gal/acre for aerial applications.
     
    B. AZOXYSTROBIN/DIFENCONAZOLE
      (Quadris Top) 10–15.4 fl oz 12 0
      MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) and Demethylation inhibitor (DMI) (3)
      COMMENTS: Apply in a 7- to 21-day interval. Do not apply more than 61.5 fl oz of product per season or 0.5 and 1.5 lb of difenoconazole or azoxystrobin, respectively, per crop. Do not make more than two sequential applications before rotating to a non-QoI group. May be applied by ground or by air. Use a sufficient amount of water to provide thorough coverage. Use a minimum of 10 gal/acre for aerial applications.
     
    C. FLUOPYRAM/TRIFLOXYSTROBIN
      (Luna Sensation) 5.0–7.6 fl oz 12 7
      MODE-OF-ACTION GROUP NAME (NUMBER1): Succinate dehydrogenase inhibitor (SDHI, 7) and quinone outside inhibitor (11).
      COMMENTS: Apply in a 7- to 21-day interval. Do not apply more than 27.1 fl oz of product per season or 0.446 and 0.5 lb of fluopyram or trifloxystrobin, respectively, per acre per year. Do not make more than two sequential applications before rotating to a non-SDHI (7) or non-QoI (11) group. May be applied by ground, air, or chemigation. Use a sufficient amount of water to provide thorough coverage. Use a minimum of 10 gal/acre for aerial applications.
     
    D. FLUXAPYROXAD/PYRACLOSTROBIN
      (Priaxor) 5.5–6.5 fl oz 12 14
      MODE-OF-ACTION GROUP NAME (NUMBER1): Succinate dehydrogenase inhibitor (SDHI) and quinone outside inhibitor (11).
      COMMENTS: Apply in a 10- to 21-day interval. Do not apply more than 44 fl oz of product per season or no more than four applications per year. Do not make more than two sequential applications before rotating to a non-QoI or non-SDHI groups. May be applied by ground or by air. Use a sufficient amount of water to provide thorough coverage. Use a minimum of 10 gal/acre for aerial applications.
     
    E. ZINC SULFATE/COPPER SULFATE/HYDRATED LIME#
      (3-2-6-100) 10–25 gal/tree See comments See comments
      MODE-OF-ACTION GROUP NAME (NUMBER1): Multi-site contact (M1)
      COMMENTS: For use on grapefruit, oranges, and lemons. Apply in 100 gal water from October through December or just after first rain. In the Central Valley, increase the amount of hydrated lime to 20 lb for the control of leafhoppers if there are high numbers of this pest; if numbers are low, use the 6 lb rate. Hydrated lime helps prevent copper toxicity under certain environmental conditions. Not all copper compounds are approved for use in organic production; be sure to check individual products. For tank mixes, observe all directions for use on all labels, and employ the most restrictive limits and precautions. Never exceed the maximum a.i. on any label when tank mixing products that contain the same a.i. Use the restricted entry interval and preharvest interval of the product with the most restrictive label of those used in the tank mix.
    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. 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 fungicide with a different mode-of-action group number.
    Text Updated: 01/19
    Treatment Table Updated: 01/19