Keep in mind, when it comes to farm workers, there are guest worker programs that provide for needed help.
This from the Center for Immigration Studies:
Notable findings:
Of the 474 civilian occupations, only six are majority immigrant (legal and illegal). These six occupations account for 1 percent of the total U.S. workforce. Moreover, native-born Americans still comprise 46 percent of workers in these occupations.
There are no occupations in the United States in which a majority of workers are illegal immigrants.
Illegal immigrants work mostly in construction, cleaning, maintenance, food service, garment manufacturing, and agricultural occupations. However, the majority of workers even in these areas are either native-born or legal immigrants.
Only 4 percent of illegal immigrants and 2 percent of all immigrants do farm work. Immigrants (legal and illegal) do make up a large share of agricultural workers — accounting for half or more of some types of farm laborers — but all agricultural workers together constitute less than 1 percent of the American work force.
Many occupations often thought to be worked overwhelmingly by immigrants (legal and illegal) are in fact majority native-born:
Maids and housekeepers: 51 percent native-born
Taxi drivers and chauffeurs: 54 percent native-born
Butchers and meat processors: 64 percent native-born
Grounds maintenance workers: 66 percent native-born
Construction laborers: 65 percent native-born
Janitors: 73 percent native-born
https://cis.org/Report/There-Are-No-Jobs-Americans-Wont-Do