Effect of Post-Emergence Applied Atrazine/Dalapon/Oil Mixture on Weed Growth and Corn Productivity

Atrazine and dalapon are used as post-emergence herbicides in corn. Dalapon is also recommended as a pre-plant soil treatment for soybean. However, the high rates of atrazine used with pre-emergence applications in corn result in the build-up of residues which adversely affect the ensuing crops of the rotation. The application of low rates of atrazine in such grain/legume rotation is desirable. The use of spray oils as an adjuvant in atrazine/dalapon mixtures would therefore be advantageous since the oil increases the post-emergence activities of atrazine. The current trial was conducted to determine the optimum levels of atrazine and dalapon, in an oil/ water emulsion, consistent with proper weed control and good corn production under Chaguaramas conditions. A simple randomised block design trial was conducted on weeds in corn (var. X 304B) grown at Tucker Valley, Chaguaramas. There were 14 treatments, replicated three times in three blocks and included four rates of a atrazine (0 to 2.24 kg. a.i. per hectare); in factorial combination with three rates of dalapon (0 to 1.12 kg. a.i. per hectare); giving 12 treatments, and two controls; an unweeded and a weed-free achieved by paraquat applications. The atrazine and/or dalapon were carried in oil/water emulsions, and applied post-emergence to the weeds and corn seedlings. Increments of atrazine and dalapon up to 1.12 kg. a.i. per hectare suppressed weed growth; the spray oil/herbicide mixture with atrazine and dalapon at 1.12 kg. a.i. per hectare respectively was the most effective suppressor of weed growth. The blanket spray application of the herbicide/oil emulsion did not affect adversely plant stand and seedling growth. In fact, grain yield increased with increments of atrazine ait the middle and high levels of dalapon. The mixture of atrazine and dalapon at 1.12 kg. a.i. and 0.56 kg. a.i. per hectare respectively in the oil/water emulsion seems to be the most suitable formulation.