Club Root This disease is a fungus within the soil, it can be identified in plants by their stunted growth especially if effected as seedlings.  It causes leaves to discolour and wilt and roots are thick and distorted. The best treatment is prevention, never grow brassicas (cabbages, cauliflower, brussel sprouts, turnips and kohlrabi) on the same soil in any three years.  Alternatively you could try a liquid club root control.

White Onion Rot A fungal rot that attacks onions, shallots and garlic as well as leeks and is at it's worst in hot dry summers.  Again the best prevention is proper crop rotation, spores can remain in the soil for at least eight years. There is no chemical control available.  Planting in overcrowded conditions makes plants particularly vulnerable.

Potato Blight This can be one of the most devastating plant diseases, it is a fungus-like organism which attacks both potato and tomato crops.  Best known for the huge losses that resulted in the Irish potato famine, the fungus attacks leaves, stems and tubers, causing them to rot and die. Tuber infection can be limited by earthing up soil around the stem and prompt removal of infected leaves may just save your crop.