Today 
Apple and pear scab is most prevalent in mild, damp seasons. The fungus overwinters on fallen leaves in the form of spores, which can be splashed by rain or carried in the wind to infect newly emerged shoots in spring. Overwintering can also occur on infected stems and branches. The most serious consequence of scab is reduced vigour of the trees caused by early leaf fall. This may limit the crop of fruit. The disease also causes scabs on the skins of fruit, although they are still edible. A preventative measure would be to use resistant varieties. Try desert apples such as Ashmeads Kernal, Discovery, Egremont Russet and cookers such as Lord Derby and Reverend.W.Wilks. For scab resistant pears try Beurre Hardy and also Josepine de malines.
Solution
Organic
Rake up fallen leaves at the end of the growing season and dispose of them - don't add them to your compost heap. Liaise with neighbours who have fruit trees to make sure they practise similar hygiene. Choose scab-resistance fruit varieties, and plant trees in open, sunny positions.
Chemical
As soon as the leaves emerge until late July, spray plants regularly with a fungicide that contains mancozeb or myclobutanil as the active ingredient.
