Brown Rot in Stone Fruit: Symptoms and Treatment

Brown rot is caused by a fungus that lives on stone and pome fruits. Sustainability expert Huan Song discusses this fungal disease and how to control, prevent, or treat it.

Written by Huan Song Horticulture review by Sarah Jay Last updated: August 23, 2024 | 4 min read

A deep red cherry infected with brown rot, appearing to have dots with a green lawn in the background

Contents

Brown rot is a group of fungal diseases that impact stone fruits and some pome fruits grown worldwide. It’s a common issue during the development of healthy fruits and a leading cause of post-harvest fruit decay in peaches, cherries, plums, and apricots. The brown rot fungi can be found on young shoots, infected twigs, open or unopened blossoms, and rotting fruit.

Brown rot diseases were first documented in 1796 and have undergone several taxonomic changes over the centuries. In 1928, these fungi were classified under the new genus Monilinia. The genus Monilinia contains around 25 species of fungi, with three species specifically causing brown rot fruit infections: Monilinia laxa, Monilinia fructigena, and Monilinia fructicola.

As with most fungal diseases, brown rot thrives under warm temperatures and humid conditions, which is why fungicides are commonly used on stone fruits. Although these three fungi species have different geographical distributions and host fruit species, they are closely related, with similar life cycles and treatment options. The control methods discussed here apply to all Monilinia species.

Brown rot is not a lethal disease for most plants but has caused significant economic losses across the world through fruit infections. Luckily, it’s been studied by agricultural researchers who have developed best practices to manage the negative impact of the disease.

What Is Brown Rot?

Three vivid red cherries with cream-colored markings caused by a fungal infection, surrounded by deep green leaves — It is a common fungal disease in California.

Brown rot fungi are a group of fungal diseases that cause fruit infections and fruit rot. M. laxa is widespread in California and throughout the U.S., except in southeastern states. It’s also prevalent in Europe, South Africa, and Chile, where it’s known as European brown rot.

M. fructicola is found in Europe, the Americas, Japan, New Zealand, and Australia. M. fructigena impacts both stone and pome fruits in Europe but is less devastating than the other two species, which can wipe out an entire crop harvest.

Life Cycle

A fruit appearing brown an rotten still dangling from the stem, surrounded by vivid green leaves, placed in a sunny area — Infections often start in warm and humid climates.

Fungal species reproduce via spores, and brown rot fungi can reproduce both sexually and asexually through two different types of spores. The fungus overwinters in cankers on twigs or as mummified fruits attached to the tree or fallen on the ground. The warm and wet weather conditions of spring kickstart the disease cycle.

In sexual reproduction, dormant spores in mummified fruit form cup structures called apothecia, which are around 5-20 mm in diameter. There can be around 20 of these cups per fallen infected fruit, and each cup contains millions of ascospores. Rainfall or other disturbances can release these ascospores, which then infect fruit tree blossoms when they come in contact with flowers or twigs, germinating as long as the plant remains wet for a few hours.

During asexual reproduction, the cankers on trees produce asexual spores called conidia, which can germinate and infect new plant tissue within 3-5 hours. These conidia are transported by wind, rain, and insects. Fruits become increasingly susceptible as they ripen due to their higher sugar content, which attracts more insects and leads to more wounds.

Symptoms

A fruit appearing brown and rotten with cream-colored spots, dangling from woody branch, surrounded by deep green and serrated leaves — It often affects fruits, but can extend to the stem and other plant parts.

Brown rot symptoms are similar across affected plants. Blossoms are susceptible to blossom blight in early spring, and diseased blossoms may wilt, turn brown, or appear covered in conidia spores. Some infected blossoms may drop, while others suffering from blossom blight may remain attached to the stem.

Infected blossoms can spread the disease to the stem, leading to the development of cankers on the bark. These cankers produce asexual spores, causing a secondary wave of infections later in the growing season. Cankers can disrupt the flow of water and nutrients, resulting in twig dieback or twig blight.

Young fruits are more resilient to brown rot fungi, but mature fruits can become infected through any injuries or openings caused by weather, handling, or insects. Fruit infections first appear as soft brown spots, which can rapidly expand to cover the entire fruit in tan and concentric rings. Infected fruits may appear covered in gray fuzz, a visible sign of the fungal spores. Sometimes, symptoms may not appear until after harvest, when infected fruits dry and shrivel, taking on a mummified appearance.

What Plants Does Brown Rot Effect?

Brown rot primarily affects stone fruits such as peaches, apricots, cherries, and plums. M. fructicola is considered the most damaging to stone fruit production. Brown rot caused by M. fructigena is more common in pome fruits like apples and pears but is less common in stone fruits.

Control

A rotten fruit appearing dark brown and dry, still dangling on woody step surrounded by green leaves with the sky in the background — Remove infected plant parts immediately.

Brown rot is not a lethal disease and can be controlled by pruning and removing cankers on fruit trees during their dormant season in the winter. Sanitize your equipment between cuts to avoid transmitting the disease by dipping tools in a solution containing 10% bleach or 70% alcohol for at least 30 seconds.

Insects are attracted to ripening fruit and can transmit the disease by creating wounds. Limiting fruit infection involves controlling insects in your orchard through integrated pest management techniques.

Fruits can exhibit brown rot post-harvest, so it’s crucial to handle susceptible ripe fruit carefully during the harvest period. Close contact in storage containers can cause the disease to spread rapidly. Refrigerate fruits immediately after harvest, as cold storage interrupts the disease cycle.

When using fungicides, carefully read the instructions and apply the chemicals according to the packaging. Fungicides are typically used at the start of the season to mitigate blossom blight and later in the season to control fruit infections. Copper fungicide is the most commonly used treatment against most Monilinia species.

Prevention

A woody brown twig with rotten fruits appearing brown, surrounded by serrated green leaves in a sunny spot in the garden — Sanitize gardening tools and dispose infected debris to control the infection.

Sanitation is key to preventing the spread of brown rot. Take care of your fruit trees by removing any dropped or infected fruit. Neglected stone fruit trees with mummified fruits can harbor brown rot fungus over the winter. Do not compost infected plant material. Remove wild prunes and other potential hosts around your orchard to decrease the reservoir of dormant fungi near your plants.

Prune fruit trees to improve air circulation in case of wet weather and humid conditions. Thinning fruits can also help by reducing the likelihood of fruits touching each other on a branch or rubbing against branches.

Some peach fruit cultivars are more resistant to brown rot than other stone fruit varieties. If brown rot is a chronic problem on your property, consider planting resistant varieties such as Elberta, Glohaven, and Babygold No. 5 as a preventative measure.

Frequently Asked Questions

While it’s difficult to completely eradicate brown rot due to its spread via microscopic spores, you can manage the infection by removing infected blossoms, twigs, and fruits, as well as eliminating other wild hosts near your orchard.