We find that buried pretty far down in the article. There is a lot of garbage in this article. One major point is that no one with a lick of common sense has ever said that the seasonal, migrant work could always be done by US citizens. It does make sense to have a guest worker program for migrant, seasonal agricultural work.
But I've read many times that US farm employers avoid using the programs for various reasons. These programs should be improved and made less cumbersome, but they should also implement reasonable means of keeping track of guest workers to ensure that they leave after a period of time.
I'd bet that, like most aspects of immigration law, that there are mountains of BS erected by those who don't want to follow the law because it's easier just to hire a bunch of illegal aliens. The government should develop workable programs and costly punishments for those who refuse to use them.