Why does my Robinia Pseudoacacia have brown patches on the leaves.
United Kingdom 
The foliage is quite sparse and looks so sad this year. what could this be, can it be treated and is it life threatening for the tree? It lives in clay soil. I live in Chorleywood, Hertfordshire
12 Jun, 2009
Is it the yellow leaved type? Over the last couple of years the RHS has been receiving lots of enquiries about Robinia 'Frisia', as many people have been having problems with them not coming into leaf fully. Unfortunately they're still trying to work out exactly what the problem is. Have a look at the following article - it might be worth getting in touch with them if this sounds like your tree's problems.
http://www.rhs.org.uk/Advice/profiles0708/robinia.asp
14 Jun, 2009