Argemone mexicana is an objectional weed in:

Argemone mexicana is an objectional weed in Rapeseed/Mustard.
An extremely hardy pioneer plant, it is tolerant of drought and poor soil, often being the only cover on new road cuttings or verges. It has bright yellow latex. It is poisonous to grazing animals.
The seeds resemble the seeds of Brassica nigra (mustard). They mature with mustard crops and may be harvested along with mustard. As a result, mustard can be adulterated by argemone seeds, rendering it poisonous.