Eli5: How do farmers keep poisonous plants from growing in crops and being harvested and packaged with edible plants?

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Eli5: How do farmers keep poisonous plants from growing in crops and being harvested and packaged with edible plants?

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The combine harvester machine actually helps take care of this. You can set the head height to be above where a lot of those are if present, and the internals of the machine are already designed to pick out the useful parts like corn kernels or grains and throw away the rest.

For stuff like strawberries etc thats usually handpicked.

Many of the crops that an unwelcome weed could enter the harvest stream are commonly hot house grown. IE; bags of mixed salad greens are mostly raised in closed systems via hydroponics, or at least narrow grow boxes. Here in PNW it is possible that hemlock grows in a backyard garden bed with other herbs like parsley. but less likely in factory farm agriculture. I’m trying to think of any circumstances something dangerous could get picked at same time. Your other veggies are easily identifiable as you go no matter how fast you grab and go.

Now that said, if it did happen it probably wouldn’t traceable. Like those e-coli outbreaks where dozens if not hundreds are sickened when a harvest is washed in a tub with an unfortunate amount of manure. A problem with the lettuce fields in the Salinas/Watsonville area, a major supplier of romain, there are cattle feed lots a few miles away and at the end of the season when it is dry as a bone, that manure can fly as dust. Odwalla had a problem when apples were harvested from an orchard that had cows freely roaming under them happily chewing the weeds growing under them.

But when those outbreaks happen, health officials interview, do some form of contact tracing, where/what did you eat the last two weeks, and when a couple commonalities get revealed they take a look at those.

But with a poisonous weed, I don’t see a scenario that would infest more than one or two bags of salad greens

Long story short… Firstly the undesirable plants are minimized in their efforts to seed by using herbicides . Later, at harvest, the combine sifts out the finished crops desirable kernel, seed, etc. You can set the desired size which helps minimize error.
Then everything else is spit out the back of the combine and ground back into the land at a later date. This provides product mostly free of anything undesirable. The farmer takes it to the local elevator for further handling/cleaning and then further processing at various stages. Yada yada.