Leaf blight on quince — symptoms and treatment

Severity: medium

What is Leaf blight

Quince leaf blight is caused by Diplocarpon mespili, a fungus that spots the leaves, strips them off early and marks the fruit. It does not kill trees outright, hence the medium severity — but premature defoliation is not a cosmetic problem. A tree that loses its leaves while the fruit is still filling cannot feed the crop or build reserves for the following season, so repeated bad years leave a quince progressively weaker. The fruit spotting is the part growers notice; the defoliation is the part that costs them.

Symptoms

It begins as small round spots on the leaves, red-brown against the green and scattered across the leaf surface. Individually they look minor. The problem is what happens next: the spots enlarge and merge into larger dead patches, the leaf yellows around them, and the tree sheds affected leaves early. In a wet season a quince can carry a thin, half-bare canopy well before autumn. The same fungus marks the fruit with dark spots, which downgrades the crop even where the flesh is sound underneath.

• Early: small round red-brown spots scattered on the leaves.
• Progressing: spots enlarging and merging; premature leaf drop, thinning the canopy.
• On the crop: dark spots on the fruit.
• Confusable with: general leaf scorch or nutrient problems — but discrete round red-brown spots that merge point to leaf blight.

Causes and conditions

The fungus survives the winter on fallen infected leaves beneath the tree, which puts autumn leaf litter at the centre of the cycle — this year's shed leaves are next year's infection. In spring, spores from that litter are splashed and blown onto the new foliage. Infection needs the leaf surface to stay wet, so prolonged rain, heavy dew and fog drive it, and a dense canopy that dries slowly extends every wet period. Once the first lesions establish they produce more spores that spread through the tree, so a wet summer delivers repeated waves rather than a single infection.

Treatment

Mancozeb — chemical

Timing: petal fall through summer. Apply fungicide from petal fall. Repeat every 10-14 days during wet weather. The programme starts at petal fall, on foliage that is still clean, because a protectant fungicide guards healthy tissue rather than curing existing spots. The repeat interval is tied to wet weather for a reason — rain both washes off the protection and creates the conditions that let spores infect. Pre-harvest interval: 14 days. Pesticide registrations vary by country — check local approval before use.

Alongside this, the highest-value action available to a home grower costs nothing: rake up and destroy the fallen leaves. That is where the fungus overwinters, and removing them cuts the source of next spring's spores.

Prevention

• Rake up and destroy fallen leaves in autumn; do not compost them near the tree.
• Prune to open the canopy so leaves dry quickly after rain and dew.
• Water at the base rather than over the canopy.
• Space trees adequately so air moves through and foliage does not stay wet.
• Begin protective sprays at petal fall, before symptoms appear, rather than reacting to spots.

Frequently asked questions

Can I eat quinces with dark spots on them? The spots are on the skin. Cut away the marked areas and the fruit underneath is usable — the damage is cosmetic rather than toxic. Observe the pre-harvest interval of 14 days after spraying.

My quince lost most of its leaves by late summer — will it die? Not from one season. Premature defoliation weakens the tree and reduces the following year's crop rather than killing it, but repeated years take a real toll. Clearing the fallen leaves and spraying from petal fall breaks the pattern.

When should I start treating? At petal fall, and repeat every 10-14 days through wet weather. Waiting until spots appear means the fungus is already established and sporulating in the canopy.