Quince Pests and Diseases: Leaf Blight, Fireblight and Fruit Rots

Quince leaf blight, the one you will meet

This is the routine problem of a quince and in a wet summer it is close to inevitable. It begins as small, sharply defined dark red-brown spots scattered across the upper surface of the leaves, no larger than a pinhead at first. Over a few weeks the spots multiply and merge, the leaf yellows around them, and the leaf falls. On a bad tree in a wet year the whole canopy can be on the ground by late summer, months before natural leaf fall.

The spots appear on the fruit too, as small dark specks and sunken patches that can crack the skin and let rots in. Young shoots can die back at the tip. The real damage is not this year's fruit, though, but next year's: a tree stripped of leaves in midsummer cannot build the shoot growth and flower buds that carry the following crop, and repeated defoliation year after year weakens it steadily.

The fungus overwinters in the fallen leaves under the tree and in infected shoots, and splashes back up onto the new leaves during spring rain. That is the whole disease cycle, and it is why the control is mechanical rather than chemical.

1. Rake up every fallen leaf In autumn, and again through the summer if leaves are dropping early, collect the litter under the tree and take it away. Do not compost it in an open heap under the same tree. This one action removes most of next spring's infection.
2. Cut out dead shoot tips Any shoot that has died back at the tip is a reservoir. Remove it back into clean wood in dry weather, cleaning the blade between cuts.
3. Open the center of the tree Air moving through the head dries leaves faster, and dry leaves do not get infected. Remove whole crowded branches in winter rather than shearing the outside.
4. Water at the roots, never over the leaves Sprinklers and overhead watering wet the canopy and splash spores upward. Soak the ground slowly instead.
5. Mulch the ground under the tree A fresh mulch each spring covers any leaf fragments you missed and stops rain splashing soil and spores onto the lowest leaves.

Fireblight, the one that kills

Fireblight is a bacterial disease and quince is among the most susceptible of all fruit trees to it. The classic sign is sudden: a shoot tip wilts, bends over into a shepherd's crook shape, and the leaves turn black or dark brown and stay hanging on the branch instead of falling, as though scorched. It moves downward through the branch and, if it reaches the trunk, will kill the tree.

It enters through the flowers in warm wet weather during blossom, and through any fresh wound, which is why pruning in the wet and heavy nitrogen feeding, which makes soft growth, both raise the risk. There is no home spray that cures it. The only treatment is to cut it out immediately and completely: remove the affected branch at least eighteen inches (45 cm) below the lowest visible blackening, into clearly healthy wood, and burn or bin the prunings.

Disinfect the blade between every single cut with alcohol or a household disinfectant, because the tool itself carries the bacteria into the next wound. If blackening reaches the main trunk, the tree cannot be saved and should be taken out before it infects neighboring apples, pears and hawthorns.

Fruit rots and the mummies left hanging

Brown rot enters through the skin wherever it is broken, whether by a blight spot, a codling moth hole, a hailstone or a bruise from careless picking. A soft brown patch spreads across the fruit, often with buff-colored pustules arranged in rings, and the fruit either falls or dries into a hard blackened mummy that stays hanging on the branch all winter.

Those mummies are the source of next year's infection and should be picked off and removed, along with any rotten fruit on the ground. Do this at the same time as the autumn leaf rake and it costs you nothing extra.

Because the entry point is nearly always a wound, gentle handling at picking is a disease control measure as much as a cosmetic one. Fruit laid down individually, in a single layer, keeps; fruit tipped from basket to tray bruises and rots within weeks.

Insects, and knowing when to do nothing

Quince has fewer serious insect problems than apple or pear. Aphids curl the soft tips of spring growth and look worse than they are; on an established tree the natural predators clear them within a few weeks and no action is needed. Persistent heavy aphid attack is a signal that the tree is being fed too much nitrogen and is making soft growth.

Codling moth caterpillars tunnel into the fruit and leave a small hole with crumbly frass at the entrance. A pheromone trap hung in the tree in early summer tells you whether the moth is present locally and reduces the numbers; picking up and destroying affected fruit rather than composting it is the other half of the answer.

Winter moth caterpillars can shred young leaves in spring and codling and sawfly damage shows up at picking. None of these is worth reaching for a spray over in a garden. The judgement to make is whether the damage is on the leaves, which the tree can absorb, or on the fruit, which you cannot.

Keep a short record of what appeared and when: the date the first leaf spots showed, whether the tree defoliated early and how much fruit was rotten at picking. Leaf blight is strongly tied to how wet your spring was, and two or three years of notes let you tell a bad season from a declining tree.