Natural control of pests and disease

As a follow on to the organic gardening, could you let us know how you use natural control of pest and disease of your garden plants 
 French marigold to control whitefly in the greenhouse
Feed the birds all year round and while they are waiting their turn at the feeder they clear insects from your flowers (it is advisable to clean below the feeders regularly as uneaten seed can encourage vermin)
If you have clubroot in your garden it is still possible to grow brassica, use cover, cloch etc. to warm up the soil and get the plants in early so that the roots establish before the fungus starts moving about June (though this date could be getting earlier now)