This will be updated as I can get to it over thanksgiving, but here are some places to start:
Once they arrive: Minutemen, and here. and here. Grassroots Yakima and here, too.
Try "Working conditions in Mexico" or Mexico poverty in search engines for reasons for leaving.
Here's one on a farmworker camp in the Valley.
Here's one on the difficult journey from Mexico to US.
Housing issues here, here and here
More on housing from a link sent by a student:
State of the State for Latinos here.
The Robots are coming. or search for "automation in orchards and packing lines"
Snokist Strike, here too.
Teamsters in Yakima, here, too.
Stemilt and unions.
Small Farmers! WSU site.
Always, Proquest and NYTimes are both good databases.