Monilia brown fruit rot

 

 

Summer brings an unwelcome guest to many fruit trees: brown rot. This disease, caused by the Monilia fungus, strikes apricots, nectarines, peaches, plums, and other stone fruits. Maturing fruit develops soft brown areas that gradually spread until they affect the entire fruit.

 

As the disease progresses, fruits may shrivel and eventually develop white powdery spores. These shriveled fruits are called "mummies.'

 

Over the winter, brown rot spores can survive on the mummies and the dormant branches. If conditions are mild and damp the following spring, the spores may infect emerging blossoms and, through them, reinfect the branches.

 

Causal organism

Monilia laxa over winters as mycelium in the cankers and the mummified parts. In winter and humid springs there is abundant conidial production on these parts in the form of postulant cushions.
The winter and spring conidia are the causes of blossom infection while the intensely sporulating summer conidia contaminate the fruits.

Conidia are produced over 10C. In high RH.
They can be dispersed by the wind or the water or transported by .
Conidial contamination is favored by the presence of wounds.
Contamination through prolonged contact between an infected and a healthy part is also possible.
The perfect form (peziza) is rare in
Europe and has little incidence in the epidemiology of this pathogen.

 

Symptoms

 

Collapse and blackening of blossoms, and shriveling of embryo fruit. Branches and twigs may crack and ooze sap.

The fungus causes wilt of the blossom which dries out and does not drop. Small grey postulant cushions occur on the peduncles of flowers.
The fruits are colonized by brown rot which rapidly invades them and shows rings of grey or pale brown postulant clumps on the surface.
In autumn the mummified fruits do not fall from the branches.
The twigs are infected by the blossom or the infected unfallen fruits via the peduncles.
The colonization of the twigs causes the cankers and the gummy exudates on the living parts.

 

 

Control

 

Clean up all affected fruit that has dropped to the ground, as well as fallen leaves that might harbor the spores. Be sure to remove any rotten or shriveled fruit and blighted twigs still on the tree. Place this infected material into a bag, seal, and discard. Don't put any diseased fruit or foliage in your compost pile.

 

You might want to place plastic netting over the tree to control birds, since their damage to the fruit can set the stage for infection.

 

To reduce the chances of recurrence, prune out wood that shows disease damage. And keep the tree pruned to let sunlight in and improve air circulation.

 

Be careful with your watering schedule. Trees that are allowed to alternate between sogginess and severe drying often develop cracked fruit which is highly susceptible to the disease.

 

Next spring, watch for signs of rotting. If you notice withering of blossoms or twigs, remove them at once and spray the tree with the fungicide benomyl (also sold as benlate and tersan).

 

If you have sprayed in the past without success, make sure you are applying the fungicide thoroughly. One spraying at the red-bud or popcorn stage (about 5 percent of blossoms open) should do the trick, unless rain occurs. In that case, reapply according to label directions.