Well, seeing as there isn't really much specific stuff being posted, here's a site that I frequently use - it just outlines some of the major problems and killers for Citrus trees.

http://www.ipm.ucdavis.edu/PMG/selectnewpest.citrus.html

It's more US based and I live in the UK, but there is a lot of relevant stuff in there for wherever you live! :)