Huata,
I agree that many immigrants are VERY hardworking, however, some of them are criminals (just as many Americans). I live in Houston, TX and we constantly hear of drug cartels smuggling and warring with border patrol. So, it's not like ALL immigrants are coming here to work hard. As I said, the majority are hard working and are a VERY loving people.
Yes, you hardly see other minorities and Caucasians working in fields, but remember, 30 years ago, this was prevalent. "Whites" and "Blacks" and other minorities used to tend their own fields when Latinos weren't. This started when our government didn't want to pay the appropriate wages for the work. So, Latinos, with the diligence to receive better lives, came to work in the fields for almost any wage.
However, today this is not the case any more. Latino Civil Rights groups began to stand up for Latinos; and in their defense, had wages raised (which was and is the correct thing to do). And this can also be attributed to many "Blacks", during the Civil Rights era/"Jim Crow", who paved the way for all people who encounter and will encounter all sorts of discrimination.
To our detriment, our American youth do NOT know ANYTHING about hard work! I am fairly young (20's) and I know my generation has a lot to learn about being appreciative. But, my parents are very hardworking and have taught me to be the same. I know about harvesting fields and crops (we've had crops on our land) and I am "Black", as well as a few other things. So, yes, Latinos are hard working, BUT they are NOT the ONLY ones who are.