Fewer than 300,000 people — many, maybe most, of them legal residents or citizens — work in the fields. Any farm worker shortage could easily be met by a LEGAL guest worker program. Indeed, the H2A visa program already exists. It just requires employers and workers to turn in the paperwork on time.
As for the rest: There was no shortage of labor in the slaughterhouse/meat packing industry prior to the post 1980s influx of illegal migration. The difference: The jobs were unionized and paid middle class wages. Housekeeping services also existed and the jobs got done before the influx of illegals.
Basically, if you’re an upper middle class type who wants cheap servants to do your housekeeping and take care of your kids, you’re down with illegal immigration. It’s the best thing to come along since those pesky Northerners abolished slavery.
Otherwise, the impact is lower market wages and identity theft.