Agriculture: Caneberries Pest Management Guidelines

Late Leaf Rust

  • Pucciniastrum americanum
  • Symptoms and Signs

    Late leaf rust infects red and purple raspberry and is not a systemic pathogen. As the name late leaf rust suggests, later in the season (beginning in July) many small rust spots are found on the older, lower leaves of raspberries. These spots first turn yellow and then brown. In severe cases plants can be defoliated, and the rust can also infect flowers and fruit. Yellow uredinia and powdery urediniospores form on the bottom sides of leaves. In fall, telia and teliospores appear as brown growth within existing uredinia.

    Comments on the Disease

    Because this pathogen's alternate host, white spruce (Picea glauca), is not common in coastal California where caneberries are cultivated, the fungus probably overwinters as mycelium within remaining canes and produces urediniospores in spring. These spring urediniospores then infect growing plants. Spores of P. americanum are spread by wind, and infection of leaves is favored by high relative humidity.

    Management

    As with yellow rust, any method that improves air circulation in the raspberry hedgerow is helpful in mitigating the spread and development of this disease. Also, the removal of infected floricanes and primocanes is useful in that it removes an important source of inoculum. The dry conditions in a macrotunnel greatly limit the infestation of late leaf rust, provided the tunnels are constructed before ideal conditions for infestation begin. In the Monterey Bay area, this generally means mid- to late July.

    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.
     
    DELAYED DORMANT
    A. FIXED COPPERS# Label rates 24 0
      MODE-OF-ACTION GROUP NAME (NUMBER1): Multi-site contact (M1)
      COMMENTS: For organically certified produce, check with your certifier for acceptable copper formulations.
     
    FIRST BLOOM
    A. FIXED COPPERS# Label rates 24 0
      MODE-OF-ACTION GROUP NAME (NUMBER1): Multi-site contact (M1)
      COMMENTS: For organically certified produce, check with your certifier for acceptable copper formulations.
     
    B. PYRACLOSTROBIN+BOSCALID
      (Pristine) 18.5–23 oz 12 0
      MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) and Succinate dehydrogenase inhibitor (7)
     
    C. PYRACLOSTROBIN
      (Cabrio EG) 14 oz 12 0
      MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
     
    D. MYCLOBUTANIL
      (Rally 40WSP) 1.25–3 oz 24 0
      MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
      COMMENTS: Initiate applications as early as budbreak and continue at 10- to 14-day intervals. Shorter intervals may be used under heavy disease pressure. Do not apply more than 10 oz/acre per season.
    # Acceptable for use on organically grown produce.
    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: 12/09
    Treatment Table Updated: 06/15