Two morphological variants ofEchinochloa crus‐galliwere collected from rice fields of an area in Greece where rice has been grown for over a decade and growers have recently been complaining about reduced effectiveness of propanil. Seedling response of the two variants to propanil was compared with that ofE. crus‐gallicollected from vegetable fields in another area where rice has never been grown. Initial contact toxicity of propanil was similar in all collections. Growth inhibition thereafter was clearly different, resulting in death of theE. crus‐gallifrom vegetables but not of theE. crus‐gallifrom rice. The latter could overcome initial toxicity and resume growth at 8 kg/ha of propanil, whereas the former was killed at 2–4 kg/ha. Prevalence ofE. crus‐galliforms of higher tolerance resulting from selection through rice husbandry and/or repeated use of propanil may account for the reduced effectiveness of propanil in the area of intensive rice growing.