American farmers grow plenty of corn and soybeans - highly mechanized and land-intensive products
America grows nowhere near enough to meet the nation’s demand for fruits and vegetables - very labor intensive products.
I think that's more about growing conditions and seasonality than labor.
America used to grow more than enough to meet the nation's demand for most of these ... when fruits and vegetables were only available in the supermarket when they were "in season." Imports made it commonplace for fruits and vegetables to be available at pretty uniform prices for the entire year. Imports also give us access to agricultural products that are difficult to grow here without heavily mechanized, energy-intensive operations (bananas, coffee, etc.).