Why Are My Pears Rotting on the Tree?

Watching pears brown, soften and develop rings of creamy-white or grey fungal pustules while still hanging from the tree is one of the most demoralising late-season sights in the orchard. Brown rot (Monilinia fructigena) is a very common fungal disease of pear and apple, and once it takes hold in a crop it can spread rapidly from fruit to fruit, particularly in warm, damp conditions close to harvest.

How brown rot spreads

Brown rot cannot infect unbroken pear skin. It enters through any wound — a codling moth or wasp feeding hole, a crack from irregular water supply, a hail injury, or simply where two fruits are touching and one is already infected. Once inside, the fungus produces brown rot at visible speed, with concentric rings of white or buff-coloured spore pustules appearing on the fruit surface within days. Airborne spores from these pustules then infect nearby fruits, spreading the disease through the hanging crop.

Mummified fruits — the hidden reservoir

Infected fruits that are not removed eventually dry out and become hard, shrivelled mummies that can hang on the tree through winter. These mummies are packed with overwintering spores and will release them directly onto next year's crop and blossoms in spring. Removing every mummified fruit from the tree in winter — even those lodged high up — significantly reduces the brown rot pressure the following season. Bag and dispose of mummies rather than composting them.

Reducing the conditions brown rot needs

Brown rot thrives in warm, humid conditions with still air. Pruning the canopy to improve air flow reduces the time leaves and fruit remain wet after rain. Harvesting at the correct time — rather than leaving fruit to ripen beyond its optimum on the tree — reduces the chance of skin cracking. Controlling codling moth and wasps reduces the entry wounds through which brown rot enters. Each of these interventions reduces risk incrementally; combined, they produce a significant difference.

In storage

Brown rot spreads in storage if infected fruit is packed alongside healthy fruit. Inspect every fruit carefully at harvest — any with wounds, soft spots or visible rot should be separated and used immediately or discarded. Store only clean, sound fruit, in a single layer if possible, so that rot from one fruit cannot contact the next. Check stored fruit every week and remove any that show signs of infection.