Effect of Time and Method of Post-Emergence Atrazine Application in Controlling Weeds in Maize

Fifteen weed control treatments comprising of atrazine 1.5 & 2.0 kg/ha as spray and broadcast with sand on 7, 14 and 21 days after sowing (DAS); atrazine 1.5 kg/ha pre-emergence spray; farmer's practice and weedy check were tested during kharif 2013 on a silty clay loam soil at Palampur. Echinochloa colona, Commelina benghalensis, Ageratum conyzoides, Cyperus sp., Digitaria sangunalis and Panicum dichotomiflorum were the important weeds. Grassy weeds were more pre-dominant than broad-leaf weeds. Preemergence spray of atrazine 1.5 kg/ha and spray of atrazine 2 kg/ha on 7 DAS were effective in controlling grassy weeds but weeds that appear late during crop growth i.e Ageratum conyzoides and Cyperus sp. were better controlled by spray of atrazine 2 kg/ha on 21 DAS. Atrazine 2 kg/ha applied on 7 DAS (spray) remaining at par with Atrazine 1.5 kg/ha applied on 7 DAS (spray), Atrazine 1.5 kg/ha applied on 14 DAS (spray), Atrazine 2 kg/ha applied on 14 DAS (spray), Atrazine 1.5 kg/ha applied on 21 DAS (spray), Atrazine 2 kg/ha applied on 21 DAS (spray) and Atrazine 1.5 kg/ha (pre- emergence spray) gave significant higher grain yield over rest of the treatments. Net returns over weedy control/check were higher under atrazine 2.0 kg/ha sprayed on 7 DAS followed by pre-emergence application of atrazine (1.50 kg/ha). Marginal benefit cost ratio was highest under pre-emergence atrazine at 1.5 kg/ha followed by atrazine 1.5 kg/ha sprayed on 7 DAS.