This article from last year sums up the considerations and herbicides available for pre-emergent use. Remember that pre-emergent applications must be followed by rain – usually around a quarter inch.
Some other weed resources available are as follows:
Almond Weed Photo Guide – With Common and Scientific Names,
Susceptibility of Winter Weeds to Herbicides,
and Weed Susceptibility Chart to Registered Herbicides.
Also, check out the weed science blog authored by UC Weed Specialist, Brad Hanson.