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Fruit tree pests and diseases

Apple Scab.

Apple Day events always bring a number of questions on Apple Scab, often accompanied by small fruit covered in a host of black spots.

Cause
This is a fungal infection caused by Venturia inaequalis. Apple scab can also affect ornamental plants such as Hawthorne, Rowan and Cotoneaster.  Crab apples are also affected.  Pears also suffer from scab but that is caused by a different fungus, Venturia pirina.

Symptoms
Scab affects the leaves and the fruit. The leaves have brown blotches on them; they are often stunted and distorted. Eventually they turn yellow and drop off. On the skin dark patches form which develops into a corky layer.  If the infection occurs early in the fruits’development, it may result in small fruit, which may crack.  Whilst scab looks unsightly, the fruit is edible and peeling the skin shows no adverse effect

Treatment
Chemical control is very difficult; spraying must be undertaken regularly throughout the growing season, using a product such as Bayer Fruit and Vegetable Disease Control or Bio Systhane Fungus Fighter, as per the manufacturers instructions.  Organic treatments are limited. The best solution being to try and break the fungus cycle which involves picking up and removing all infected material in the Autumn – leaves and fruit.  If this cannot be done mow under the tree to break up infected material and apply a dusting of garden lime to aid rapid decomposition.  Some organic gardeners are known to collect urine to make a 1 in 10 dilution to spray on the trees (after the fruit has been picked!).  A similar treatment is used by growers, using the eqivalent of 6 grams of Urea per litre of water, which equates to around an ounce to the gallon. This is done around the 23rd October.  When pruning remove and destroy any infected material.  Scab can be seen on young branches, the bark looking a-typical.  Cut out and burn infected material.  Check susceptible ornamental plants also and treat in a similar manner.  Prevention is always better than a cure, and if starting from scatch consider planting scab resistant varieties, if this is not possible, then keep susceptible varieties as far apart as possible.
Some traditional apple cultivars that are resistant to scab include:

  • Ashmeads Kernel,
  • Belle de Boskoop,
  • Cheddar Cross,
  • Discovery,
  • Edward VII,
  • Ellisons Orange,
  • Emneth Early,
  • Fortune,
  • Golden Noble,
  • Grenadier,
  • Howgate Wonder,
  • King of the Pippins,
  • Lanes Prince Albert
  • Lord Lambourne,
  • Millers Seedling,
  • Monarch,
  • St Edmunds Pippin,
  • Sunset,
  • Winston

There are also a number of new apple cultivars that have been trialled in the UK and found to grow successfully, they include Christmas Pippin, Limelight, Herefordshire Russet, Rajka, Red Devil, Resi, Rubinola, Scrumptious and Topaz