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Brown Rot on Apricot and Other Stone Fruits

Brown rot is a fungus that affects apricots, nectarines, peaches, plums, and other stone fruits. Recognizing symptoms and understanding the disease cycle can help you control it.

• Symptoms
• Disease Cycle
  • Management
  • Resistant Cultivars
  • Sanitation — Cultural Control
  • Minimize Fruit Injury — Cultural Control
  • Chemical Control

Brown rot is a common and destructive disease affecting apricot and other stone fruits (cherry, nectarine, peach, and plum) in Nebraska. This fungus may attack blossoms, fruit spurs (flower and fruit bearing twigs), and small branches. Most damage from this disease occurs when fruit becomes infected just prior to ripening, or during and after harvest. When environmental conditions are conducive, the entire crop can completely rot on the tree. Following harvest, fruit that is not kept cool during storage may rot in two or three days.

Symptoms

The symptoms of brown rot are similar on all stone fruits. Symptoms first appear in the spring as the blossoms are beginning to open. Infected blossoms turn brown, wither, and die. Blossoms may be covered with a brownish-gray mass of spores. Occasionally the blossoms may become fixed to twigs as a gummy mass; however, the blossoms usually remain attached throughout the summer. Infection at this stage reduces fruit set but increases inoculum levels available for fruit infections later in the season. The young, developing fruit are normally resistant but can become infected through wounds (e.g., insect feeding, hail damage). As the fruit matures it becomes susceptible to infection even in the absence of a wound(s). Initially symptoms appear as soft brown spots, which quickly expand and produce a mass of tan powdery spores called conidia (Figure 1). As the infection proceeds, it will cover the entire fruit, causing the fruit to rot rapidly. The fruit then dries and shrinks into a wrinkled “mummy” (Figure 2). Typically the rotted and mummy fruit remain attached to the tree. Fruit infections may spread rapidly, especially if weather conditions are conducive for disease development and the fruit are touching one another.

Figure 1. Brown rot infecting apricots and producing spores on the surface of infected apricots. These spores can infect other fruit. Photo courtesy of Loren Giesler, University of Nebraska–Lincoln.		Figure 2. Brown rot mummy from an infected apricot with production of fungal spores on the surface. Photo courtesy of Loren Giesler, University of Nebraska–Lincoln.

The fungus may infect the spurs of the tree through infected blossoms and/or fruit. Twigs develop an elliptical canker with profuse gumming at the margin between healthy and infected tissue. Infected twigs may become girdled and killed. Leaves attached to an infected twig typically turn brown and wither (twig blight). Occasionally, succulent shoots are infected by direct penetration near their tip.

Disease Cycle

Brown rot is caused by the fungus, Monilinia fructicola. This fungus overwinters in mummified fruits (either on the ground or still on the tree) and in twig and branch cankers produced the preceeding year. Sporulation of the fungus is favored by moderate temperatures (55° to 77°F) and wet weather; however, spores can be produced at temperatures ranging between 32° and 90°F. The spores are spread to blooms, new shoots and/or fruit by wind, rain-splash, and insects such as bees or beetles (Figure 3). The spores infect plant tissues after being exposed to a water film for five hours or more.

Figure 3. Brown rot disease cycle.*

*We want to thank the New York State Integrated Pest Management Program and Cornell University for use of this figure. Taken from Brown Rot of Stone Fruits Disease Identification Sheet No. 10, 1993.

Management

Effective management includes both cultural and chemical approaches. The integration of multiple tactics provides the best long-term management option.

Resistant Cultivars

The majority of commercial stone fruit cultivars are susceptible to brown rot infection when favorable conditions are present during the three-week ripening window. Tables I and II lists the susceptibility of some peach and apricot cultivars currently available.

Sanitation — Cultural Control

Sanitation is critical in effectively managing brown rot. During the dormant season, mummified fruit and cankers should be pruned and either burned, buried deeply in the soil, or sent to the landfill. This will reduce the amount of overwintering inoculum present. Remove wild or neglected stone fruit trees in the area that serve as a reservoir of spores. During the growing season, remove and destroy overripe or rotting fruit on the orchard floor and/or packing sheds to reduce the amount of secondary inoculum.

Minimize Fruit Injury — Cultural Control

Fruit feeding insects create openings and wounds on the fruit where brown spot infections occur. Controlling those insects will reduce the amount of fruit infection. It is important to remember that any type of wound on the fruit surface is a prime location for brown rot infection. Take special care during harvesting and packing to prevent punctures and bruising. Cooling or refrigerating the fruit as close to 32°F as possible immediately following harvest will slow the development of the fungus in storage.

Chemical Control

Regular, well-timed fungicide sprays effectively control brown spot infections when used in combination with cultural methods. Properly using both protective and systemic fungicides (Table III) protects flowers and fruits. It also reduces the amount of sporulation on infected tissue and reduces overwinter inoculum levels.

Apricots: Apricots are very susceptible to blossom blight. Typically one protective spray should be applied each year and repeated at full bloom and/or at petal fall (Table IV) if warm conditions exist during bloom. To protect the fruit, a shuck-split (Table IV) application also should be considered.

Cherries: Sweet cherry is more susceptible than sour cherry to blossom blight. For sweet cherry, a petal fall (Table IV) spray is recommended if the weather is warm and wet because the fruit is very susceptible the first few weeks after fruit set.

Peaches and Nectarines: For these stone fruits, rarely more than one blossom blight spray is needed unless the disease is severe. A fungicide application at petal fall (Table IV) is only necessary if an earlier application was not made and conditions continue to be warm and wet. An application at shuck split and first cover (Table IV) sprays are important when the weather is wet because the fruit is the most susceptible one to three weeks following shuck split.

Plums and Prunes: An application to prevent blossom blight is only needed if there is a large number of unharvested fruit still remaining on the tree. Fungicide application at shuck split and first cover (Table IV) spray are important for plums because the fruit is very susceptible for the first few weeks after setting.

This publication has been peer reviewed.

This publication has been peer reviewed.