Fruit rot (nutmeg)
Developing nutmeg fruit rots on the tree during the monsoon — premature splitting, discoloured tissue and ruined mace. Canopy pruning, sanitation and timely copper sprays are the main defences.
- Pathogen
- Colletotrichum gloeosporioides + Diplodia theobromae
- Starts at
- Developing fruit on the tree
- Favoured by
- Monsoon humidity, poor canopy ventilation
- Best defence
- Pruning, sanitation, copper sprays, resistant varieties
Overview
Nutmeg fruit rot is caused by the fungi Colletotrichum gloeosporioides and Botryodiplodia (Diplodia) theobromae, separately or together. The disease attacks developing fruit on the tree: water-soaked lesions appear on the pericarp, the tissue discolours and softens, the outer husk may split prematurely (before normal ripening), and the mace and seed inside are spoiled. Diplodia rot in particular can blacken and destroy the mace while the fruit is still on the tree.
The disease is most severe during the monsoon months — June through September — when humidity is high, rain keeps the canopy wet and air circulation is poor in unpruned trees. Dense canopies, overlapping branches and overcrowded gardens worsen it. The main practical defences are keeping the canopy open through pruning, removing and destroying fallen rotten fruit (which harbours inoculum for the next season), timely copper-based preventive sprays, and choosing varieties with reported low fruit-rot incidence (IISR Viswashree and IISR Keralashree).
How to identify it
- Water-soaked, dark lesions appear on the surface of the developing fruit.
- The fruit tissue softens, discolours (brown to black) and may start oozing in wet weather.
- The outer husk splits open prematurely — before normal ripening — exposing the nut and mace inside.
- The mace (the red, net-like aril that wraps around the seed) turns discoloured, slimy or blackened instead of its normal bright scarlet.
- The nut inside may also be rotten or have a foul smell.
- Fallen fruit under the tree often shows advanced rot and is a source of inoculum.
Why it happens
- The fungi Colletotrichum gloeosporioides and Botryodiplodia (Diplodia) theobromae, both common tropical pathogens, infect nutmeg fruit during the monsoon when continuous wetness and high humidity favour spore germination and spread.
- Dense, unpruned canopies that trap moisture and restrict air flow create ideal conditions.
- Fallen rotten fruit on the ground harbours the fungus through the dry season and releases spores at the start of the next monsoon.
- Wounds from insects or physical damage provide entry points, but the fungi can also infect intact fruit tissue under favourable conditions.
How to manage it
- Prune overlapping branches to open up the canopy and improve air circulation — this is the single most effective structural measure.
- Collect and destroy (burn or deep-bury) all fallen rotten fruit promptly. Do not let it accumulate under the tree.
- TNAU advises spraying with 1% Bordeaux mixture or copper oxychloride at 0.25% during the monsoon, starting before the main fruiting season. Confirm the current product and dose with your KVK.
- Avoid overhead irrigation or anything that keeps the canopy wet for long periods.
- Choose varieties with reported low fruit-rot incidence — IISR Viswashree and IISR Keralashree have this documented advantage.
Crops most at risk
Where this problem is called out in our crop guides — open a crop for the full package of practices.
Varieties to consider
Named seed varieties whose resistance or susceptibility to this problem is documented on their own variety page.
Frequently asked questions
Can nutmeg fruit rot be cured once it starts on a fruit?
No — once a fruit is visibly rotting, it is lost. The goal is to prevent the next cycle: remove rotten fruit, prune for air circulation and spray copper-based fungicides preventively during the monsoon. The disease is managed by reducing inoculum and conditions, not by curing individual fruit.
Which nutmeg varieties are less affected?
IISR Viswashree and IISR Keralashree, both released by ICAR-IISR Kozhikode, have documented low incidence of Diplodia fruit rot. No variety is immune, but starting with one of these is an advantage.
Symptoms and control measures follow ICAR, KVK and state agricultural-university package-of-practices; any named chemical is a registered use. Always read the product label and confirm the dose for your crop and zone. editorial policy.