Brown Rot of Stone Fruits (Monilinia fructicola)

Brown rot is a fungus that may cause serious damage to stone fruits during wet seasons. Prolonged wet weather during bloom may result in extensive blossom infection. Early infections appear as a blossom blight or twig canker. Later infections appear as a rot of ripening fruit on the tree and in storage. Spring infections arise from mummified fruit of the previous season that remains attached to the tree or has fallen to the ground.

• Symptoms
• Life Cycle
• Disease Management
  • Cultural Control
  • Chemical Control
  • Stone Fruit Fungicide Table - Resistance Management Groups

Symptoms:

Apricot brown rot - shoot blight

Blossom Blight: Infected blossoms wilt, shrivel and become covered with greyish mold. Petals may appear light brown or water-soaked, similar to frost injury. Blighted blossoms do not produce fruit.

The amount of blossom blight directly affects the amount of fruit rot. Dead blossoms may stick to spurs and twigs until harvest, providing a source of spores for the fruit rot phase.

Twig Blight and Canker: On peaches and apricots the infection may spread to twigs, causing brownish, oval cankers that may girdle and kill twigs. Gumming may also occur on infected twigs.

Fruit Rot: Fruit rot first appears as small, circular brown spots that increase rapidly in size causing the entire fruit to rot. Greyish spores appear in tufts on rotted areas. Infected fruit eventually turn into shriveled, black mummies that may drop or remain attached to the tree through the winter. Brown rot can be serious on injured fruit such as cherries split by rain.

Brown rot on plum, cherry, apricot and peach fruit Cherry and peach photographs courtesy Agriculture & Agri-Food Canada

Young green fruit can be infected just before shuck fall, but the infection often remains inactive until near maturity.

Brown rot can spread after harvest. Mature fruit can decay in only 2 days under warm conditions.

Note that Botrytis rot is also common, particularly on cherries, and symptoms appear similar to brown rot. Correct diagnosis of the rot present is an important consideration when selecting fungicides.

Life Cycle:

Spring infection: Two types of spores are produced in spring which can infect blossoms. Conidia are produced on cankers and fruit mummies in the tree. Apothecia (small mushroom like structures) form on mummies lying on the ground. The apothecia discharge ascospores during the bloom period, but don't contribute to fruit infection later in season. Fruit mummies hanging in the tree are thought to be the main source of initial inoculum in the BC interior.

Secondary Infection: Spores produced on blighted blossoms provide a source of infection for ripening fruit. Infected fruit become covered with greyish spores which spread by wind and rain to healthy fruit. Insects may also contribute to spread of brown rot spores.

Conditions for infection: Brown rot is more of a problem during wet seasons. Prolonged wet weather during bloom may result in extensive blossom infection. The length of wet periods required for blossom infection depends upon the temperature. The chart below illustrates the length of wet period required for blossom infection to occur at various temperatures.

Temperature	Hours of Wet Required For Blossom Infection
26oC	2
21oC	3
16oC	4
07oC	6-7
04oC	11-12

Disease Management

1. Orchard sanitation: Remove and destroy fruit mummies when pruning. Prune out any cankered or dead twigs as they are found. Removing rotten fruit from the tree will reduce initial inoculum. Removing fallen fruit from the ground is less practical, but may be an option in small blocks or for organic growers. Although sanitation alone is not sufficient to control brown rot in most commercial orchards, it is a good IPM control strategy. Sanitation will decrease inoculum levels, which will improve the effectiveness of fungicide sprays. Fungicidal control may not be as good as desired when disease pressure is very high.
2. Pruning: Some cherry varieties such as Lapins tend to produce large clusters of fruit. Brown rot may develop in these clusters more easily due to difficulty of obtaining good fungicide coverage and slower drying of fruit in the middle of the clusters. When pruning remove excessive branches to allow for increased air flow and shorten current season’s growth to reduce fruit cluster formation.
3. Avoid injuring or bruising fruit at harvest. Pick only sound fruit. Discard fruit with brown spots or rot. Dispose of culls and rotted fruit promptly by burying. Pre-cool and keep fruit in cold storage until it reaches destination.

Chemical Control

1. Blossom - Orchards with a history of brown rot require one or more sprays to protect blossoms. Spray when first blossoms open. If wet weather occurs repeat spray at 50 per cent bloom and at full bloom. Select blossom sprays from the following lists of fungicides:

   (a) Cherries: Rovral (iprodione), Indar (fenbuconazole), Topas or Mission (propiconazole), Elevate (fenhexamid), Lance (boscalid), Captan (Maestro), Nova (myclobutanil), Bravo 500 (chlorothalonil), Senator (thiophanate-methyl) or Funginex (triforine). Note: Do not exceed 3 Bravo applications per year, and do not apply Bravo after shuck split to avoid fruit injury. Do not apply Vangard to cherries, as it is no longer registered for cherry and will cause severe leaf burning on some varieties.

   (b) Peaches: Rovral, Indar, Topas, Mission, Elevate, Lance, Captan, Bravo 500, Nova, Senator, Funginex, Vangard, or a tank mix of Vangard plus Rovral or Nova. Note: Do not exceed 3 Bravo applications per year, and do not apply Bravo after shuck split to avoid fruit injury. Do not apply Vangard more than 2 times for blossom blight control.

   (c) Nectarines: Indar, Topas, Mission, Elevate, Lance, Captan, Bravo 500, Nova, Senator or Vangard. Note: Do not exceed 3 Bravo applications per year, and do not apply Bravo after shuck split to avoid fruit injury. Do not apply Vangard more than 2 times for blossom blight control.

   (d) Prunes and plums: Rovral, Indar, Topas, Mission, Lance, Captan, Vangard, Senator or Funginex. Do not apply Vangard more than 2 times for blossom blight control.

   (e) Apricots: Rovral, Indar, Topas, Mission, Lance, Vangard or Captan. Do not apply Vangard more than 2 times for blossom blight control.

2. Ripening fruit- Apply one of the following sprays when the fruit changes colour and a second spray just before picking. Additional sprays may be needed with wet weather. On cherries, prunes and plums the quantity of captan may be reduced for the final pre-harvest spray to 2.75 kg/ha to avoid unsightly residues. Do not exceed 2 applications of Topas or 2 applications of Vangard for fruit rot control. Controlling insects, particularly those pests that directly injure fruit, helps to prevent infection.

   (a) Cherries: Rovral (iprodione), Indar (fenbuconazole), Topas or Mission (propiconazole), Elevate (fenhexamid), Lance (boscalid), Nova (myclobutanil), Captan (Maestro), Senator (thiophanate-methyl).

   (b) Peaches: Rovral, Indar, Topas, Mission, Elevate, Lance, Captan, Nova, Senator, Vangard or a tank mix of Vangard plus Rovral or Nova.

   (c) Nectarines: Indar, Topas, Mission, Elevate, Lance, Captan, Nova, Senator, Vangard or a tank mix of Vangard plus Nova.

   (d) Prunes and plums: Rovral, Indar, Topas, Mission, Lance, Vangard, Captan or Senator.

   (e) Apricots: Rovral, Indar, Topas, Mission, Lance, Vangard or Captan.

3. Immature Fruit – In most Okanagan orchards fungicide coverage on the blossom and ripe fruit stages are sufficient for good brown rot control. However orchards with a history of brown rot problems may want to consider fungicide coverage of green fruit, particularly if weather is wet. Fruitlets are most susceptible prior to shuckfall.

4. Mature Fruit – Ripe fruit ready to be picked, especially apricots and peaches, are very susceptible to brown rot infection. A pre-harvest application of a brown rot fungicide immediately before harvest (1-3 days) is needed to provide these fruit with an adequate shelf life. Generally the shelf life is approximately three weeks for treated fruit kept at around 13^oC. For this application use only fungicides that have a minimum preharvest interval of three or less days.

5. Fungal resistance to fungicides- such as Senator (formerly known as Easout) and Rovral has developed on many crops throughout the world. Vangard, Nova, Indar, Topas, Mission, Lance and Elevate are also at risk for resistance. Alternate fungicides with different modes of action, or use registered tank mixes to reduce the risk of resistance developing in your orchard.

• Stone Fruit Fungicide Table - Resistance Management Groups