Common quince (Cydonia oblonga) is very often affected by this leaf spot disease, particularly in wet summers. The vigour and cropping of the tree may be reduced in severe cases.

On affected trees, quince leaf blight leads to a number of symptoms;

• Small dark spots with grey centres are formed on the leaves
• Numerous spots can develop on a single leaf – these may coalesce and the leaves turn brown or yellow and fall prematurely
• Spotting and distortion of the fruits may also occur
• Infected shoot tips can die back

The RHS believes that avoiding pests, diseases and weeds by good practice in cultivation methods, cultivar selection, garden hygiene and encouraging or introducing natural enemies, should be the first line of control. If chemical controls are used, they should be used only in a minimal and highly targeted manner.

Non chemical

• Rake up and dispose of affected leaves as they fall, and also the rest of the leaves during autumn leaf fall
• Prune out any dead shoots during the winter
• Maintain good cultivation, especially feeding to help the tree grow more foliage
• There are differences between quince cultivars in their susceptibility to leaf blight. The wet summer of 2023 was very favourable for the disease, and in the quince collection at RHS Wisley the cultivars 'Serbian Gold' and 'Aromatnaya' showed good tolerance. They still developed leaf spots, but these remained small compared to those on susceptible cultivars, and they had little or no premature leaf fall

Fungicides

The RHS recommends that you don't use fungicides. Fungicides (including organic types) may reduce biodiversity, impact soil health and have wider adverse environmental effects. If you do intend to use a fungicide, please read the information given in the link and download below to ensure that use, storage and disposal of the product is done in a responsible and legally compliant manner.
  
The products listed in the ‘Fungicides for gardeners’ document below are legally available for use by home gardeners in the UK. This information is provided to avoid misuse of legal products and the use of unauthorised and untested products, which potentially has more serious consequences for the environment and wildlife than when products are used legally. Homemade products are not recommended as they are unregulated and usually untested.

There is no specific information available on the efficacy of any home garden fungicide against quince leaf blight. No fungicides are currently available for use on trees from which the fruit will be consumed.

Download

Fungicides for gardeners (Adobe Acrobat pdf document outlining fungicides available to gardeners)

Link

Chemicals: storing and disposing safely

The fungus overwinters on dead twigs and on fallen leaves, and spores produced on these start new infections in the spring. Once the first leaf spots have formed, fruiting bodies develop within them, and the spores that they produce are splashed in rain droplets to create further infections on the leaves, shoot tips and fruit. The disease is therefore most severe during wet summers.

Diplocarpon mespili can also affect numerous other plants in the family Rosaceae, causing leaf spots and blotches (often similar in appearance to those on quince). Apart from common quince, it is seen most frequently on hawthorn, medlar, pyracantha and pear. However, outbreaks on these hosts are sporadic and usually far less damaging than those on quince.