Agriculture: Floriculture and Ornamental Nurseries Pest Management Guidelines

Fungal Leaf Spots, Blights, and Cankers

  • Alternaria blight of carnation: Alternaria saponariae (formerly A. dianthi)
  • Black spot of rose: Diplocarpon rosae
  • Cercospora leaf spot of statice: Cercospora insulana
  • Leaf blotch of peony: Cladosporium paeoniae
  • Leaf spot of aster: Stemphylium callistephi
  • Ovulinia petal blight of azalea: Ovulinia azaleae
  • Symptoms and Signs

    Foliar diseases caused by plant pathogenic fungi result in a wide range of symptoms that vary greatly depending on the particular pathogen and the host plant. Leaf spots (also called leaf lesions) are discrete, diseased sections of leaves that initially may be dull green or yellow in color, but later turn brown, black, or display another abnormal color. Leaf spot shapes also vary greatly, but usually are oval, oblong, or round. Leaf petioles can also develop such spots. The occurrence and merging of numerous leaf spots results in the infection of large portions of the foliage; such symptoms are called blights. Infections on twigs and branches can cause cankers, which are sunken, discolored, and cracked areas in the woody tissue. In many cases, the mycelium and fruiting structures of the pathogenic fungi will grow on top of the diseased leaf spot, blight, and canker areas.

    Comments on the Disease

    There are many different kinds of foliar fungal diseases of flower and nursery crops. In many cases these fungi are host specific and will only infect one plant species. Most of these organisms produce spores that are spread by wind currents and splashing water from rain or sprinklers. Moist, humid conditions are needed for infection and disease development. Some of these fungi are carried in the seed; all can be carried in infected cuttings and other propagative material.

    Management

    Use pathogen- and disease-free seed, cuttings, transplants, and other propagative materials. Implement sanitation measures when dealing with containers, flats, benches, pruning tools, and other items that come in contact with plants. Avoid using overhead sprinkler irrigation. Rogue out diseased cuttings, transplants, and plants. Sanitize hands or gloves after handling diseased plants. Fungicides provide some control.

    Common name Amount to use REI‡
    (Example trade name) (hours)
    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. Strobilurins such as AZOXYSTROBIN, PYRACLOSTROBIN, TRIFLOXYSTROBIN and FLUOXASTROBIN
      (Heritage, Compass O 50WDG) Label rates See label
      MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
    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.
    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.
    Text Updated: 11/20
    Treatment Table Updated: 11/20