Ayrshire,
United Kingdom 
3 years ago I planted a green gooseberry bush which has done really nicely, 2 years ago a red gooseberry was sited next to it, did fine too. What happened this year was that someone gave me a blackcurrant (which I do not even like, but thought I might just as well try) and I planted it next to the gooseberries (due to lack of space somewhere else. Now the green gooseberry is covered in American Mildew. (The red one is absolutely fine, it's a resistant variety anyway.) I suspect as blackcurrrant is a carrier of this mildew (googling told me) that that's the reason the gooseberry looks so dreadful. I do organic gardening and do not want to use chemical fungizides, any suggestions what to do? Thanks.
30 May, 2011
Answers
6d is right on the mark. Increase the air movement through the bush. You could also try bicarbonate of soda (baking soda) and water with just a touch of vegetable oil. The mix is 1 tbsp of soda to 1 gallon of water with about 1 tsp of oil. Mix it up and spray both tops and bottoms of the leaves.
Both the milk mix and the soda mix work by changing the pH of the leaf surface and thereby making it inhospitable for the fungus to grow.
31 May, 2011
Previous question
« an attrative medium size shrub for a shady spot in the garden
Fruit bushs like airiation and pruned when too thick and air can't get through and around them, 1 part milk to 10 parts water and spray should do the mildew, not sure what american mildew is though.
31 May, 2011