Nottinghamshire,
United Kingdom 
orange powder on my patio trees
29 Aug, 2010
Answers
You haven't said what the trees are, but if they're Kilmarnock Willows, it will be rust. Needs an appropriate fungicide spray, though it won't do much this year, but spray at the first hint of its return next year.
29 Aug, 2010
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possibly rust?--- not being silly, plants can get rust-- try google for pictures
29 Aug, 2010