You can try, but the unemployment levels in the USA have not generally been low enough to find enough workers in total in recent decades. Worse, even the last few % of unemployment is a deliberate policy choice to prevent a rapid cycle of wage inflation as everyone competes for a limited supply of workers:

The farmers would have to pay enough for "seasonal work spending all day doing manual labour in the sun without any AC" to compete with "year round work spending all day stacking shelves in supermarket where the temperature is at consistently in the range that doesn't put off the customers". And if the farmers got the former shelf stackers, then the supermarkets need to find more people to do the stacking. Food prices go up, both wholesale (because the farmers have to pay workers more) and retail beyond that (because so do the supermarkets).

I keep seeing stories about poorer Americans struggling with food prices even without this kind of cycle; but it doesn't end with just those two examples, it's all the low-pay jobs that are inherently more comfortable than farm labour, and if they find themselves short of labour and raise wages they too have to raise prices to balance their books, and whichever professions they in turn get labour from have the same choices, it ripples across the entire economy. Which may be good or bad for other reasons, but it's a massive impact across the entire economy, not something which is an easy one-liner.

Also, despite all those issues, look at this from the point of view of those workers: They've got seasonal work that pays them somewhat more than they'd earn in their home countries, and until very recently that work would not have come with a risk of being deported to a completely different country than they'd come from.