A naturally occurring prickly lettuce biotype resistant to a 5:1 formulated mixture of chlorsulfuron:metsulfuron (DPX-G8311) was identified in a no-till winter wheat field near Lewiston, ID, in April, 1987. Field and greenhouse studies were established to evaluate its resistance to other sulfonylureas, imidazolinones, and herbicides with alternate sites of action. The resistant biotype resisted eight sulfonylurea herbicides; resisted the imidazolinone herbicides, imazapyr and imazethypyr, but not imazaquin; and resisted no other herbicides included in the studies. The resistant biotype was identified in seven of nine fields on the farm where it was discovered.

Sulfonylurea herbicide resistance was crossed into a susceptible (S) prickly lettuce biotype and into ‘Bibb’ (B), a domestic lettuce cultivar, and inheritance of the resistance trait was determined. The best fit for Chi Square analysis of the metsulfuron treated F2 generations was a 1:2:1 ratio indicating the trait was controlled by a single nuclear gene with incomplete dominance. F3 generations also were treated with metsulfuron. The F3 seedlings from resistant F2 plants were resistant while the F3 seedlings from intermediate F2 plants segregated.