My small apple orchard is always attacked by fruit worms and fungi. How can i prevent this?

Hmmm. Oddly enough, I was just doing a bit of light reading (a lot of gardening type books under the Xmas tree!)and cross-referenced to page 234 of Rodale's "Garden Answers" 1995 edition.
The section is called "Solving Apple Problems" and covers Symptoms, Causes and Solutions, pages of them! I will now dutyfully type what pertains:

Fruit Symptoms:
Deep corky scars or indentations on fruit
Causes:
Fruitworms, Leafrollers, Tarnished Plant Bugs.
Solutions:
Ripe deformed fruit do not contain insects and are edible. If you see lots of caterpillars feeding on leaves, spray tree with BTK or Neem. remove and destroy rolled up leaves.
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Alternatively:

Apple maggots (dimpled, knobby fruit) note brown tunnels in fruit, discolored areas. Hang sticky traps to attract and catch adult flies next year.
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Fungi - small black spots, wipe fruit with a damp cloth to remove harmless fungi.

Tree or branch symptoms:

Prune out and destroy cankers, allow wounds to dry and then paint large wounds with a 1:1 mix of white interior latex paint and lime-sulphur.

I dunno...but perhaps this will be helpful!
John in Victoria BC Canaduh
ecologicals1@shaw.ca
http://www.ecologicalsgardens.com/

With the multitude of different pests that can attack at different stages of the fruit growth, it can be difficult to judge the proper times to apply cides. And the fact that you have ongoing pest problems tells me that your particular ecosystem is out of balance somehow.
Every organic garden/orchard needs a diversity of plants that will host a variety of different insects that will control the bad ones, I call this the scales of justice program. It is also important to provide birdhouses right on site for more benefit.

Even with a diversity of predators available once established, there always is a chance that the scales can temporarily tip towards the favor of disease or pests, so for extra protection against pest and disease such as scab I prefer to use a physical barrier product such as kaolin clay, you can find the product at gardens alive! If you are in the U.S. there is no source in Canada right now apart from myself, but I only offer it as a service package at present time.

You need to start a good spray program and probably need to prune the trees as well.

Getting good apples is an intensive job of spraying one thing or the other every 5 days or so.

Spraying starts in late winter with dormant oil (do this after pruning-no need to be spraying wood that is coming off). This gets rid of a lot of overwintering pupas and scale.

When the leaves start coming out you spray lime sulfur and do that again several times until the flowers appear.

After petal fall other sprays are needed-Bt, bordeaux mix if fungus is still a problem, kelp, soap for aphids.
You also can put sticky traps in the trees at this time-red balls covered with a product like Tanglefoot and hung from branches

You need to thin the baby apples so there is just one per node in June and it is very very inportant to pick up all dropped apples at least twice a week. many bugs lay their eggs in the fruit and the larva wait for the fruit to fall and than in a week or so burrow into the ground to pupate. Remove the fruit and they cannot get in the ground to pupate.

This year we are trying a new product called Surround which is Kaolin clay that is sprayed on the trees and turns them white. This is supposed to fool the insects. They don't recognize apple trees that are white and stay away. The clay also dries up fungus and does a few other good things.

A good book on the subject is The Apple Grower by Michael Phillips.