Persistence of Annual Applications of Herbicides in Winter-planted Safflower (Carthamus tinctorius)

Diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea], prometryn [2,4-bis(isopropylamino)-6-(methylthio)- s -triazine], and trifluralin (α,α,α-trifluoro-2,6-dinitro- N,N -dipropyl- p -toluidine) were applied pre-plant in safflower ( Carthamus tinctorius L. ‘AC-1′) for 6 yr at two locations. Diuron and prometryn reduced crop stands in 2 of 6 yr on the sandier soil at Mesa. Growth of sorghum [ Sorghum bicolor (L.) Moench ‘Amak R-10′] in the greenhouse in soil collected 10 months after each herbicide application was reduced by 1.7 kg/ha of trifluralin in 3 of 6 yr in the Yuma silty clay loam and by both rates of trifluralin in 1 of 6 yr in the sandier soil at Mesa. Growth of barley ( Hordeum vulgare L. ‘ Arivat ’) was not reduced in soil treated with any herbicide at either location. Herbicides did not accumulate in winter-planted safflower.