This soft-focus map shows Chalara fraxinea outbreaks in our region as of April this year. It does not look too alarming. But the disease is spreading rapidly and DEFRA now expects that 50% of ash trees in West Sussex will be infected by 2018. If you own ash trees you will probably want to take a look at the report [PDF] they issued on 30th April. Conveniently, it also covers the Oak Processionary Moth. In addition, they have issued a synopsis of the relevant research [PDF].
The Forestry Commission has released an app for Apple and Android devices that will assist you in recognizing and reporting tree diseases: