Evaluation of the Relative Phytotoxicity of Herbicides to Cotton and Nutsedge

Abstract

The following herbicides were evaluated for relative phytotoxicity to cotton (Gossypium hirsutum L. ‘Acala SJ-1′), purple nutsedge (Cyperus rotundus L.), and yellow nutsedge (Cyperus esculentus L.) under greenhouse conditions: 2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide (alachlor); 2-chloro-2′,6′-diethyl-N-(butoxymethyl)acetanilide (CP-53619); 2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione (VCS-438); 4-chloro-5-(dimethylamino)-2-α,α,α-trifluoro-m-tolyl)-3(2H)-pyridazinone (San-6706); 2-(α naphthoxy)-N,N-diethyl-propionamide (R-7465); and S-isopropyl 5-ethyl-2-methyl-piperidine-1-carbiothioate (R-12001). Herbicides were incorporated 6.35 cm deep, at rates of 1.12, 2.24, and 4.48 kg/ha, into a fine sandy loam prior to planting. All treatments except the low rate of alachlor and VCS-438 controlled yellow nutsedge for 8 weeks. R-7465 and R-12001 at 1.12 kg/ha and San-6706 at 2.24 kg/ha controlled purple nutsedge for 8 weeks. Alachlor and CP-53619 were somewhat less effective against purple nutsedge than yellow nutsedge, but their intermediate rates suppressed purple nutsedge for 4 weeks. Even the high rate of VCS-438 was ineffective against purple nutsedge. Cotton, in terms of fresh shoot weight, exhibited considerable tolerance to 1.12 and 2.24 kg/ha of VCS-438 and CP-53619 and 1.12 kg/ha of R-7465. Applications of 2.24 kg/ha of CP-53619 and 1.12 kg/ha of R-7465, however, suppressed the development of lateral roots of cotton. Other rates of these herbicides and all rates of alachlor, R-12001, and San-6706 moderately to severely injured cotton in most of the experiments.