Summary. Field experiments were conducted to find a herbicide for complete control of nutsedge (Cyperus rotundus L.). We applied seventeen herbicides and some of their combinations as chemical fallow. EPTC and CP‐31675 (6‐tert‐butyl‐2‐chloro‐o‐acetotoluidide) gave good but only temporary control of nutsedge. Dichlobenil at 2·5 or 5 lb/ac gave fair control for 1 year. Rates of 10 or 20 lb/ac of dichlobenil controlled nutsedge completely for 1 year but severely reduced the yield of oats planted 5 months after application. The highest rate completely killed tubers and prevented reinfestation for 1 year. Analyses indicated no residue of dichlobenil or of its metabolite, 2,6‐dichlorobenzoic acid, in vegetative parts and seeds of oats planted 5 months after application of 2.5, 5 or 10 lb/ac of dichlobenil. At equivalent rates the herbicide TH‐073‐H (N‐hydroxymethyl‐2,6‐dichlorothiolbenzamide) gave control of nutsedge similar to that with dichlobenil. The combinations of 8 lb/ac amitrole‐T and 10 lb/ac dichlobenil or TH‐073‐H were just as effective in controlling nutsedge shoots and tubers as dichlobenil or TH‐073‐H applied alone. The mixture of dichlobenil plus CP‐31675, each at 5 lb/ac, gave excellent control of nutsedge and tubers for 1 year. The herbicides terbacil (3‐ter‐Nbutyl‐5‐chloro‐6‐methyluracil) or Du Pont 733 (3‐tert‐butyl‐5‐bromo‐6‐methyluracil) at 10 lb/ac provided almost complete control of nutsedge. Application of terbacil to plants aged 4–6 weeks gave better results than application to mature nutsedge in the fall. La lutte chimique contre le cypirus Copyright © 1969, Wiley Blackwell. All rights reserved
