Brown rot on apricot — symptoms and treatment

Severity: high

What is Brown rot

Brown rot is caused by Monilinia laxa and M. fructigena. It is the most destructive disease of apricots, especially in wet springs — hence its high severity rating. What makes it so damaging is that it strikes twice: once at bloom, destroying the flowers that would have become fruit, and again as the crop ripens, rotting apricots on the tree and continuing to spread in the picking basket. A crop that looked perfect a week before harvest can be largely lost to it.

Symptoms

The first phase is blossom blight. Flowers brown, wilt and collapse but hang on the spur instead of falling cleanly, and the infection runs from the blossom down into the twig, producing small cankers and killing shoot tips. The second phase appears on ripening fruit as a brown, rapidly expanding rot, soft under the thumb, spreading from a single point until the whole apricot is involved. On the rotted surface, concentric rings of grey spores develop — tufted, dusty pustules arranged in rings, the diagnostic sign. Rotted fruit dries and hardens into mummies that stay attached to the branch through winter.

• Early signs: browning, collapsing blossoms that cling to the spur; a soft brown spot on a ripening fruit
• Advanced signs: brown expanding rot with concentric rings of grey spores, twig cankers, mummified fruit hanging on the tree
• Confusable with: other fruit rots — the rings of grey sporulation plus blighted blossoms on the same tree confirm brown rot

Causes and conditions

The fungus overwinters in mummified fruit and twig cankers, and these are the launching point for each new season. Spores are released in wet weather and carried by wind, rain splash and insects onto open blossoms, which is why a wet spring at bloom produces a severe year and a dry one may pass almost unnoticed. Later, spores from blighted blossoms and cankers infect ripening fruit. Warm, humid weather near harvest accelerates it sharply, and any break in the skin — insect punctures, hail, bird pecks, splits from rain on ripe fruit — gives an easy entry. Fruit touching fruit in a crowded cluster lets the rot pass directly from one to the next.

Treatment

Remove mummified fruit — cultural

Timing: winter dormancy. Remove all mummified fruit from the tree and ground during winter. Prune for air circulation. Take the mummies and prunings away from the site. Every mummy left hanging is next spring's spore source aimed directly at your blossoms.

Thiophanate-methyl + Captan — chemical

Timing: bloom and pre-harvest. Apply at bloom (blossom blight prevention) and pre-harvest (fruit rot prevention). Critical in wet springs. Pre-harvest interval: 14 days. Pesticide registrations vary by country — check local approval before use.

Prevention

• Strip every mummified apricot from the tree and clear fallen fruit each winter
• Prune for an open canopy so blossoms and fruit dry quickly after rain
• Thin fruit so apricots do not touch — contact spreads the rot through a cluster
• Handle fruit gently and control insect damage; unbroken skin resists infection
• Pick promptly at ripeness and cool the fruit — brown rot keeps spreading after harvest

Frequently asked questions

Can I eat apricots from an affected tree? Discard any fruit showing rot. Sound, unblemished fruit from the same tree is fine, but check it carefully — infection often starts as a small soft spot that is easy to miss, and one rotting apricot will spread to those packed around it.

When is spraying most important? At bloom, particularly in a wet spring. Blossom infection is what seeds the fruit rot later, so protecting the flowers is the highest-value timing. A second application before harvest protects the ripening crop.

Why does it come back every year? Mummified fruit and twig cankers carry the fungus through winter on the tree itself. If they are not removed during dormancy, the disease restarts each spring regardless of spraying.