Brown Rot

Monilinia fructicola

Fungalalso: Brown rot blossom blight

The most serious disease of stone fruit, brown rot blights spring blossoms and twigs and then rots the ripening fruit, sometimes turning a sound peach to mush within a day. It hits peaches, nectarines, plums, cherries, and apricots, and in warm, wet weather it can destroy much of a backyard crop on the tree and in storage.

🔎 How to spot it

In spring, look for blossoms that suddenly wilt, brown, and stick to the twig, with small cankers and oozing gum where the blight runs into the wood. On ripening fruit, look for small brown spots that spread fast over the whole fruit, soon covered with tan to gray tufts of powdery spores. Rotted fruit shrivels into a hard, dark mummy that may cling to the branch over winter.

🥀 Damage it causes

Brown rot kills blossoms and the twigs behind them, and then rots fruit as it ripens and after harvest, so that fruit can collapse within hours in warm, humid weather. A bad year can cost most of the crop, and the mummified fruit and twig cankers carry the fungus into the next season.

🔬 What causes it

Brown rot is caused by the fungus Monilinia fructicola, which overwinters in mummified fruit and twig cankers. In spring its spores infect open blossoms, and later, wounds and ripening fruit, with warm, wet, humid weather strongly favoring infection and spread. Insect injury and skin breaks give the fungus easy entry into the fruit.

🛡️ Prevent it

Plant where air moves and sun reaches the fruit, and prune for an open canopy that dries fast. Remove and destroy every mummified fruit and pruned-out cankered twig, the key overwintering sources. Thin fruit so they do not touch, control the insects that wound fruit, and avoid wetting blossoms and fruit when watering. Choose less susceptible varieties where you can.

🧯 If it is already here

Pick and destroy rotting and mummified fruit promptly so they do not seed new infections. On susceptible trees in wet springs, protectant fungicides applied at early bloom and again at full bloom, and as fruit nears ripening, reduce infection; follow the label. Sanitation, removing mummies and cankers, plus good airflow does much of the work without spraying.

💡 Good to know

The clinging brown mummies are both the diagnostic sign and the fungus winter home, so stripping them off the tree and the ground each year breaks much of the cycle. Brown rot moves astonishingly fast in warm, humid weather, which is why prompt removal of the first rotting fruit matters so much. Bagging individual fruit can protect a small backyard crop.

For educational and informational purposes only. Disease management advice is general guidance drawn from university cooperative extension sources; always identify a problem positively and read and follow the label on any product before use, especially around food crops, children, and pets.