Pacific Northwest 1998 An Online Guide to Plant Disease Control

FactSheets offer superior print quality for the page you are currently viewing. Using Microsoft's Internet Explorer has given best printing results.
Glossary
Guide Home
Search

OSU Extension Office
 
Plum, Flowering -- Brown Rot Blossom Blight
 
Cause: The fungi Monilinia fructicola and M. laxa can incite both a blossom blight, a twig and branch dieback. Fungi survive year to year on infected twigs, branches, old flower parts, or mummified fruit of other Prunus sp. Conidia are produced on infected plant debris in the tree when the temperature is above 40°F. A small, mushroom-like structure (apothecium) can be produced on fruit that drops to the ground. Wind and rain blow spores (conidia and ascospores) to healthy blossoms in spring to begin the infection process during wet weather. Infection does not occur below 50°F and will occur for M. laxa above 55°F. Flowers can be blighted any time floral tissue is exposed but are most susceptible at full bloom. More spores can be produced on this tissue, initiating several more disease cycles during the spring. Under severe conditions, non-flowering shoots or leaves can be infected directly. Both fruiting and ornamental plums (purple leaf plums), peaches, nectarines, prunes, cherries, almonds, and apricots are susceptible. Susceptible cultivars include Prunus X cistena, P. X blireiannna while resistant cultivars include P. cerasifera ‘Frankthrees’ (Mt. St. Helens), ‘Krauter Versuvius,’ ‘Newport,’ and ‘Thundercloud.’
Symptoms: Infected flower parts turn light brown and may develop areas of buff-color (M. fructicola) or gray (M. laxa) spores. Infected petals may look water soaked, which can be mistaken for frost injury. Flowers generally collapse as the fungus invades through the pedicel. Infected flowers often adhere to twigs and spurs through harvest or even winter. Depending on the fungus and plant infected, the disease may continue into twigs or spurs. Lesions may remain discrete or girdle the twig, causing all distal portions to die. Profuse gumming also may occur in these areas. Again, buff or gray spores (in sporodochia) may develop on these necrotic twigs.

Shoot dieback and dead flowers due to brown rot.

 
Cultural control: These must be supplemented by chemical control methods especially in the wettest areas such as west of the Cascades.
  1. Remove and destroy infected twigs and branches in summer.
  2. Use moderate amounts of nitrogen fertilizer.
  3. Plant resistant cultivars.
Chemical control: Do not use on edible fruit or within 12 months of harvest. Only one (1) or two (2) applications during bloom are needed most years. Fungi are at risk of developing resistance to many of these chemicals; rotate materials of different families from application to application. See labels for details.
  1. 26 GT Fungicide at 1 to 2.5 quarts/A. 12-hr reentry.
  2. Banner MAXX at 2 to 4 fl oz/100 gal water. 24-hr reentry.
  3. Daconil Weather Stik at 1.4 pints/100 gal water. Daconil can be used in home gardens. 12-hr reentry. H
  4. OHP 26 GT-O at 1 to 2.5 qt/100 gal water with a maximum of 2.5 qt/A. Limit to two (2) applications per year to aid resistance management. 12-hr reentry.
  5. Spectracide Immunox at 1 fl oz/gal water.
  6. Thiophanate-methyl-based products. 12-hr reentry.
    1. Cleary’s 3336 WP at 12 to 16 oz/100 gal water.
    2. Halt (by ferti-lome) at 2.5 tsp/gal water is registered for home use. H
Content edited by: on January 1, 2009
 
Top

In print since 1954 and on the web since 1996. Questions or comments, please contact us.