Brown Rot Pre-Harvest Alert

Early infections appear as blossom blight or twig canker where the infected blossom turns brown and dies. Cankers oozing gum are often found at the base of dead blossoms on infected shoots. Once the fruit begins to ripen and change color, it becomes more susceptible. The brown rot pathogen can gain easy access to fruit when any type of injury caused by insect damage, hail injury, bird pecks, bruising and / or cracking, etc. is present. Later infections appear as a rot of ripening fruit on the tree and in storage. The most obvious symptoms of brown rot occur in ripening fruit. It first appears as a small spot that quickly enlarges within 2 to 5 days until the whole fruit is rotten and becomes covered in a mass of light grey-brown spores. If left on a tree, it will shrivel and dry out. This mummified fruit will carry spores over the winter and will be the main source of blossom infection in the following spring.

Brown rot is spread by wind, rain splash and insects. Dew can provide enough moisture to allow infection of ripe fruit. The two most susceptible periods for fruit infection are prior to pit hardening and 2 to 4 weeks before harvest.

Symptoms

Brown rot causes blossom blight, twig blight, twig canker and fruit rot. 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.

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 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.

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 within 48 hours under warm conditions.

Disease Cycle – what do we need to know?

Overwintering. The fungus overwinters in mummified fruit on the ground or in the tree, and in twig cankers.

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

Secondary Infection. Spores produced on blighted blossoms provide a source of infection for ripening fruit. Infected fruit become covered with greyish-brownish 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 length of a wetting period required for infection to occur at various temperatures.

Disease Management – back to basics

In areas with wet and humid weather, efficient and effective management of brown rot requires both cultural and chemical controls.

Cultural Control

Sanitation practices that reduce the amount of fungal inoculum are integral to brown rot control. Most important is removing as much infested plant material as possible to reduce overwintering fungal inoculum. Pruning practices that promote good air circulation and sunlight penetration into the tree canopy also can help to prevent conditions that favor infection and development of the brown rot pathogen.

• Prune out 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. 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.
• Avoid injuring or bruising fruit at harvest. 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

The protectant approach is the best control strategy.

• Spray effective fungicides (3 to 4 weeks before harvest) when the fruit changes color. Additional sprays may be needed with wet weather. Control insects that cause fruit injury. In a dry season, fungicide coverage on the blossom and ripe fruit stages are sufficient for good brown rot control. However, in orchards with a history of brown rot problems, consider fungicide coverage of green fruit, particularly if weather is wet. Fruitlets are most susceptible prior to shuck fall.
• Ripe fruit ready to be picked are very susceptible to brown rot infection. An application of a brown rot fungicide immediately before harvest (1 to 3 days) is needed to provide fruit with an adequate shelf life.

Fungicide Resistance Management

Fungicide resistance management is important to prolong the effectiveness of "at risk" fungicides and to limit crop losses should resistance occur.

To help prevent resistance from developing:

• Alternate between different fungicide groups (see Table 2). Do not use more than two back-to-back sprays of fungicides with the same group number. In particular, use products rated with a medium to high risk carefully, and limit the number of applications. Products with a low risk of resistance can generally be used more often.
• Use recommended tank mixes.
• Use only recommended dose rates.
• Ensure sprayer is properly calibrated to deliver accurate and thorough coverage.
• Integrate with non-chemical control methods.
• Discontinue use of a product if resistance is suspected and consult your crop advisor.
• Always read the fungicide label requirements before making any application.

Fungicides registered in Pennsylvania for use on stone fruit for brown rot and/or powdery mildew, categorized by resistance group.

*M = multi-site inhibitor; NC = not classified.

Fungicides in the same group have similar or identical modes of action. Over-use of fungicides in the same chemical group will lead to resistance problems. Some fungicides labeled for use in stone fruit may be familiar, but others will be new. Do read the fungicide label carefully, as generic products may have different labels from brand name products and from each other.

Reference resources:
www.Agsci.psu.edu/tfpg. PA Tree Fruit production Guide 2012.
www.frac.info/frac/publication/anhang/FRAC-Code. Fungicides Resistance Action Code List 2012.
www.http://omafra.gov.on.ca/english/crops/facts/peach_pests/brown_rot.htm.
www.cdms.net/LabelsMsds.