Pacific Northwest 1998 An Online Guide to Plant Disease Control

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OSU Extension Office
 
Peach -- Brown Rot
See Also: Cherry -- Brown Rot Blossom Blight and Fruit Rot
 
Cause: The fungi Monilinia fructicola and M. laxa can incite both a blossom blight, a twig and branch dieback, and a fruit rot of several Prunus sp. including many ornamental and fruit trees. Fungi survive year to year on infected twigs, branches, old flower parts, or mummified fruit. Conidia are produced on infected plant debris in the tree when the temperature is above 40°F. A small, mushroomlike 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 will occur for M. laxa above 55°F. Infection may occur at any temperature above freezing with 24 hours wetness. 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.

Some infections may be symptomless until fruit begins to ripen. Ripening fruit also is highly susceptible to infection, and many more disease cycles can occur near harvest. Peach and nectarine fruit that fall to the ground due to lack of pollination, thinning, or overripeness can significantly increase inoculum and the amount of fruit rot at harvest. Fruit infected in the orchard may not show symptoms until it is in storage or in transit. High nitrogen fertilization also is associated with increased levels of brown rot.

Both fruiting and ornamental cherries, peaches, nectarines, prunes, plums, almonds, and apricots are susceptible. The disease is more a problem west of the Cascades. Surveys of eastern Washington packinghouses during 2000 and 2001 found very little brown rot on peaches and nectarines.

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. On peach, the disease continues into twigs or spurs. Lesions may remain discrete or may girdle the twig, causing all distal portions to die. Profuse gumming also may be in these areas. Again, buff or gray spores (in sporodochia) may develop on these necrotic twigs.

Fruit symptoms begin as small, dark spots that enlarge rapidly. Fruit remains fairly firm and dry relative to a watery rot caused by Rhizopus sp. Production of masses of buff-colored spores is equally rapid in the necrotic area. Peaches may have concentric rings of gray sporulation as the rot takes a few days to encompass the entire fruit.

Note the zones of gray sporulation on the lowest peach.

Rotted peaches mummify and may cling to the tree well into the next growing season.

Blossom infections result in necrotic lesions on the stem. This stem has completely died back.

This shows brown rot of the blossom which results in a twig canker. Note the ooze droplet at the end of the brown cankered area, and sporulation on the blossom.

 
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. Remove and destroy all mummified fruit in and around the tree. Cultivating or burying old fruit before the growing season will not reduce the risk of this disease. However, removing fallen fruit (due to thinning or lack of pollination) can significantly reduce the amount of rot at harvest.
  3. Control insects that could wound and injure fruit.
  4. Avoid wounding fruit during harvest.
  5. Cool fruit rapidly after harvest.
  6. Use moderate amounts of nitrogen fertilizer.
  7. A short (2.5 min) soak in hot water (122°F) has reduced postharvest decay in nectarines and peaches. Some additives have increased efficacy of this treatment.
Chemical control: Apply fungicides during the blossoming period at early pink bud, full bloom, and/or petal fall to control the blossom blight phase. In California, one or two sprays are sufficient most years if a product with systemic (translaminar) activity is used. Fruit rot sprays can be applied before harvest if wet weather is expected. To reduce the possibility of resistant fungal strains, alternate or tank-mix fungicides that have a different mode of action. Alternating Indar and Rally for example, is not suggested since both have the same mode of action.
  1. Abound at 12 to 15.5 fl oz/A. Alternate with other fungicides. Do not apply more than 4 times/year or 2 sequential sprays. May be applied the day of harvest. Sprayers used for Abound should not be used on apples such as Gala, Cox's Orange Pippin and McIntosh. 4-hr reentry.
  2. AuxiGro WP at 4 oz/A plus a silicone-based surfactant. For blossom blight only. Unknown efficacy in the PNW. 4-hr reentry.
  3. Botran 75 W at 1.3 to 5.3 lb/A. Do not apply within 10 days of harvest. 12-hr reentry.
  4. Bravo Weather Stik at 3.1 to 4.1 pints/A. Do not apply after shuck split. Do not use more than 20.5 pints/A/season. 12-hr reentry.
  5. Captan 80 WDG at 2.5 to 5 lb/A. Applications may be made day of harvest. Hi-Yield Captan Fungicide 50 WP may be used in Oregon home gardens at 2 Tbsp/gal water.
  6. Echo 720 at 3.1 to 4.1 pints/A, for blossom blight only. Do not apply after shuck split. 12-hr reentry.
  7. Elevate 50 WDG at 1 to 1.5 lb/A. Applications may be made up to and including the day of harvest. Do not use more than 6 lb/A/season. 12-hr reentry.
  8. Elite 45 DF at 4 to 8 oz/A. Do not apply more than 3 lb/A per crop season. Can be applied up to and including day of harvest. 12-hr reentry.
  9. Indar 2F at 6 fl oz/A plus a wetting agent. Do not exceed 48 fl oz/A/season. 12-hr reentry.
  10. Iprodione based products. Do not apply after petal fall or more than two (2) times per season. Generally good control if resistance is not a problem. 24-hr reentry.
    1. Iprodione 4L AG at 1 to 2 pint/A.
    2. Nevado 4F at 1 to 2 pint/A.
    3. Rovral 4 Flowable at 1 to 2 pint/A.
  11. Microthiol Disperss(80% sulfur) at 10 to 20 lb/A. Do not use a spreader sticker. Only slight control; not recommended for use during bloom. 24-hr reentry.
  12. Orius 45 DF at 4 to 8 oz/A. Can be applied through the day of harvest. 12-hr reentry.
  13. Pristine at 10.5 to 14.5 oz/A. Do not use more than 2 consecutive applications or more than 5 times/year. Can be used day of harvest. 12-hr reentry.
  14. Propiconazole-based fungicdes are registered. Limited to 4 applications (2 during bloom and 2 before harvest). May be used up to and including day of harvest.
    1. Bumper 41.8 EC at 4 oz/A. Do not use on Stanley-type Plums. 24-hr reentry.
    2. Orbit at 4 oz/A. Do not use on Stanley type Plums earlier than 21 days before harvest.12-hr reentry.
    3. PropiMax EC at 4 fl oz/A. Do not use on Stanley type Plums earlier than 21 days before harvest.24-hr reentry. 24-hr reentry.
    4. Tilt at 4 oz/A. Do not use on Stanley type Plums earlier than 21 days before harvest. 12-hr reentry.
  15. Quash at 2.5 to 4 oz/A. Do not make more than 3 applications/year or within 14 days of harvest. Group 3 fungicide. 12-hr reentry.
  16. Quilt (propiconazole + azoxystrobin) at 14 fl oz/A. Do not apply more than two (2) sequential sprays. May be applied the day of harvest. 12-hr reentry.
  17. Rally 40 WSP at 2.5 to 6 oz/A. Can be applied up to the day of harvest. Not as good as the manufacturer’s other DMI-type fungicide, Indar. Use Eagle 20 EW at 2 to 3 fl oz/100 gal water for landscape use. 24-hr reentry.
  18. Scala SC at 9 to 18 fl oz/A. Do not apply more than 3 applications alone, more than 54 oz/A/season, or within 2 days of harvest. Not for cherry—only for apricot, peach, prune and plum. 12-hr reentry.
  19. Spectracide Immunox at 0.5 fl oz/gal water. May be applied up to the day of harvest. Do not use more than 7 times per season.
  20. Syllit FL at 3 pt/A. Blossom blight only. Do not use after petal fall. 48-hr reentry.
  21. Thiram Granuflo at 3.9 to 5.1 lb/A. Do not apply within 7 days of harvest. Also serves as an animal repellant. 24-hr reentry.
  22. Topsin 4.5 FL at 20 to 30 fl oz/A plus another fungicide with good protection activity. Do not apply within 1 day of harvest. Halt (by ferti-lome) is registered for home use. 12-hr reentry.
  23. Vangard 75 WG at 5 oz/A. For blossom blight only. Do not apply more than 10 oz/A/season. Tank-mix with another fungicide to improve efficacy and to manage resistance. 12-hr reentry.
  24. Ziram 76 DF at 6 to 8 lb/A. Do not apply within 30 days of harvest. Generally, gives slight control. 48-hr reentry.
Notes: Fixed copper products are registered but due to low level of control are not recommended.
Biological control:
  1. Serenade MAX (Bacillus subtilis strain QST 713) at 1 to 3 lb/A. Labeled only for fruit rot control. Active ingredient is a protein. 4-hr reentry.
Content edited by: Jay W. Pscheidt on January 1, 2009
 
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