Brown Rot on Fruit Trees: Prevention and Treatment Guide

What Brown Rot Is

Brown rot is a fungal disease of peaches, nectarines, plums, apricots and cherries that blights blossoms, kills twigs and rots fruit as it ripens. To control it, remove every dried fruit mummy and cankered twig after harvest and in winter, pick off rotting fruit as soon as it appears, and apply a labeled fungicide at bloom and again in the last weeks before harvest. Penn State Extension notes that mature fruit can completely decay in 2 days from the time of infection, so prevention matters more than rescue.

University of Wisconsin Extension identifies the cause as two fungi in the genus Monilinia, primarily Monilinia fructicola and less commonly Monilinia laxa. The hosts are trees and shrubs in the genus Prunus, which covers all the common stone fruits.

Weather drives the disease. Wisconsin reports that brown rot can occur across a wide range of temperatures, 40 to 86°F, but tends to be more of a problem when the weather is warm, 68 to 77°F, and wet. Clemson adds that spores infect healthy green fruit during long wet periods. A rainy week at bloom or just before picking is the classic setup for heavy losses.

Signs on Blossoms, Twigs and Fruit

Brown rot looks different on each part of the tree, and the first signs arrive in spring, weeks before any fruit is at risk.

Where	What you see	Source
Blossoms	Flowers wilt and turn brown very quickly. Dead blossoms often cling to the twig for a long time.	Clemson, UC IPM
Twigs	The infection moves from the flower into the shoot and forms a small, gummy canker 1 to 3 inches long that can girdle the twig.	Clemson, Penn State
Fruit	A small, round brown spot expands until the whole fruit is rotten.	Clemson
Any infected part in damp weather	Ash-gray to brown or tan tufts of spores on the surface.	Penn State, UC IPM
After the rot	Fruit dries into a mummy that hangs on the tree or falls to the ground.	Wisconsin

The spore tufts are the most recognizable sign. Look for them on browned flowers and at the edges of fruit spots in humid weather.

Fruit becomes much easier to infect when the skin is broken. Penn State says wounded fruit is more susceptible and that insects carry spores to injury sites created by oriental fruit moth, Japanese beetle and other pests. Wisconsin lists sap beetles, vinegar flies and honeybees among the insects that can transport spores, and notes that further spread occurs when infected and healthy fruits touch.

How the Fungus Survives From Year to Year

The disease returns each spring from material left on or under the tree. According to Wisconsin, brown rot fungi overwinter on infected twigs and in mummified fruits that are hanging from trees or have fallen to the ground. Penn State names the same three sources: mummies formed the previous season, blighted twigs and cankers.

In wet spring weather those sources release spores, which Penn State describes as being forcibly ejected into the air and blown by the wind to blossoms. Clemson describes the twig cankers that follow as a source of infection, with spores from infected flowers and cankers reaching green fruit in long wet periods. Clemson also points out that infected fruit tends to stay on the tree instead of dropping normally, which keeps a spore source hanging among the ripening crop.

This cycle is the reason sanitation works. Every mummy and canker taken out of the tree between harvest and bloom is one less starting point for the next season.

A Season Plan for Prevention and Treatment

The work falls into two kinds, cleanup and spraying, and each has fixed points in the season. Cleanup comes first because it costs nothing and lowers the pressure the sprays have to hold back.

Fall and winter. Penn State calls removing all mummies and blighted twigs after harvest important for reducing the amount of fungus that overwinters. Clemson says to remove all dried fruit mummies from the tree in the fall, since that is where the fungus survives the winter, and to remove cankered wood during winter pruning. Clemson also says to collect and dispose of diseased fruit on the ground. Wisconsin’s advice for all of this material is to burn it where local ordinance allows or bury it deep. For the cuts, Wisconsin’s instruction is to prune 4 to 6 inches below sunken or dead tissue on each branch.

Tool care. Wisconsin recommends disinfecting pruning tools between cuts by treating them for at least 30 seconds in a 10 percent bleach solution or, preferably, 70 percent alcohol, which is less corrosive. Rubbing alcohol is about that strength. If you use bleach, rinse and oil the tools afterward to prevent rust, and see removing rust from garden tools if it has already started.

Growing season. Clemson says to collect and remove diseased fruit from the tree as it appears. Do not wait for a scheduled cleanup day, because a single rotting peach coated in spores sits inches from its neighbors.

Bloom and ripening. These are the two spray windows, covered in the next section.

Fungicide Timing and Products

Penn State states that fungicide sprays are necessary during bloom and as the fruit ripens. The extension services agree on those two windows and differ on the exact schedule, partly because they write for different climates and crops.

Source	Bloom timing	Fruit timing
University of Wisconsin Extension	When about 10 percent of flowers are open	Begin three weeks before anticipated harvest
Clemson, for peaches in South Carolina	Full bloom, then two more sprays at 10 to 14 day intervals	From first color change, at 7 day intervals, typically three times until harvest
Penn State, for peaches	During bloom	At 18 days, 9 days and 1 day before harvest
UC IPM, for California	Pink bud stage	When fruit starts to color, if rainy weather persists

For active ingredients, Wisconsin says to select products labeled for apricots, cherries, peaches or plums that contain captan, myclobutanil or propiconazole. Clemson lists captan, myclobutanil and wettable sulfur for peaches and notes a minimum pre-harvest interval of one day for those fungicides. UC IPM mentions copper-containing fungicides or myclobutanil at pink bud, with a firm limit: do not apply copper compounds after bloom.

The label on the product you buy sets the rate, the crops it may be used on and the days to wait before picking. Follow it over any general schedule, including the ones in this table. How sulfur and copper compare with other options is covered in organic fungicides for home gardens.

Habits That Lower the Pressure

A tree that dries quickly after rain gives the fungus less time to infect. UC IPM advises pruning trees to allow good ventilation, and when you plant, give each tree enough room that the canopies stay separate at full size.

Keep irrigation water off the tree. UC IPM recommends furrow irrigation or low-angle sprinklers to avoid wetting blossoms, foliage and fruit.

Break up fruit clusters. Because rot spreads where infected and healthy fruits touch, thinning peaches and plums so that fruits hang apart removes an easy route from one to the next.

Manage the insects that wound fruit. Penn State calls it critical to stay on top of insect management, because wounded fruit are much more susceptible than unwounded fruit, and it names oriental fruit moth, Japanese beetle and green June beetle among the insects that injure fruit.

Handle the harvest with care. Penn State warns that fruit that looks healthy at picking can still decay later in storage, and Wisconsin advises storing fruit in a cool, not overly wet environment. Pick promptly and keep bruised or split fruit apart from the sound ones.

For new plantings, UC IPM suggests choosing the least susceptible varieties available locally. Ask about brown rot when you compare bare-root and potted trees at the nursery.