Fruit rot (heart rot) on pomegranate — symptoms and treatment

Severity: medium

What is Fruit rot (heart rot)

Fruit rot (heart rot) is caused by Alternaria and Aspergillus species that enter the pomegranate through the flower. What makes it unusual is that the internal rot is invisible from outside: the fungi colonise the inside of the developing fruit while the skin grows normally over the top of it. There is no lesion to spot and no spray that reaches the damage once it is inside, so everything effective happens at flowering — long before anyone would think to look for a rot.

Symptoms

The defining symptom of this disease is the absence of symptoms. From the outside an infected pomegranate looks normal — right colour, right shape, no spots, no cracks. Cut it open and the arils are brown and rotten instead of red and juicy, sometimes as a partial wedge, sometimes throughout. Growers usually discover it one fruit at a time at the kitchen counter. The other clue comes earlier: infected fruit tends to drop prematurely, so a tree shedding apparently sound pomegranates is worth investigating with a knife. Affected fruit also carries an off-flavour.

• Outside: normal-looking fruit exterior — no reliable external sign.
• Inside: arils brown and rotten when the fruit is cut open; off-flavour.
• On the tree: premature fruit drop.
• Confusable with: nothing visible — the only way to confirm is to cut fruit open.

Causes and conditions

The infection route is the flower. Spores reach the open bloom, establish there, and are carried inside as the fruit develops around them — which is why the fungus ends up sealed within intact fruit. Both are common fungi that persist on plant debris and rotted fruit around the tree, so an orchard that leaves fallen fruit lying provides its own inoculum for next year. Wet, humid weather during bloom favours infection, since the spores need moisture to establish in the flower. Cracked fruit gives a second entry point later, and cracking is driven by irrigation that swings between dry and wet.

Treatment

Harvest timing — cultural

Timing: at harvest. Harvest promptly when ripe. Avoid fruit cracking by consistent irrigation. Remove damaged fruit. Consistent irrigation keeps the skin from splitting, closing off the second infection route, and prompt harvest limits how long fruit hangs exposed. Removing damaged fruit clears the material the fungi build up on.

Carbendazim — chemical

Timing: at flowering. Apply fungicide sprays at flowering to protect against fungal entry through the flower. The timing is the entire point — the flower is the door, so protection has to be there while the bloom is open. A spray applied to developing or mature fruit does nothing about a rot already sealed inside. Pre-harvest interval: 14 days. Pesticide registrations vary by country — check local approval before use.

Prevention

• Protect the bloom, not the fruit — the infection happens at flowering and nothing later reaches it.
• Irrigate consistently to avoid the swings that split fruit skin and open a second entry route.
• Harvest promptly once fruit is ripe rather than leaving it hanging.
• Remove and destroy damaged, dropped and rotted fruit instead of leaving it under the tree.
• Cut a sample of fruit open at harvest — it is the only way to know whether a block is affected.

Frequently asked questions

How do I know if my pomegranates have heart rot before I cut them? Realistically, you cannot. The exterior looks normal, which is what defines this disease. Premature fruit drop is the one hint worth acting on — cut a few dropped fruit open and see what the arils look like.

Can I eat a fruit with some brown arils? No. Discard fruit with brown, rotten arils and the off-flavour that comes with them. This is fungal rot inside the fruit, not cosmetic damage you can cut around.

When should I spray? At flowering. That is when the fungi enter, and it is the only window where a fungicide can protect against them. Observe the pre-harvest interval of 14 days.