Activity, adsorption, mobility, efficacy, and persistence of alachlor as influenced by formulation

Activity, adsorption, mobility, and field persistence of one emulsifiable concentrate (EC) and three microencapsulated (ME) formulations of alachlor were studied with petri dish bioassay, based on root response of oats grown in sand or soil. Both bioassays indicated that activity of all formulations was increased with increasing herbicide concentration. EC-alachlor in sand showed the highest activity, while ME-alachlor(L) and ME-alachlor(A), the lowest; the activity of ME-alachlor(C) was intermediate. In silty clay loam soil, EC-alachlor had the highest activity, while ME-alachlor(L) had the lowest; and ME-alachlor(A) showed intermediate activity and was similar to that of ME-alachlor(C). More alachlor was adsorbed on the soil or remained encapsulated (not biologically available) after ME-alachlor(L) and ME-alachor(A) application compared to EC-alachlor. An intermediate amount of alachlor was adsorbed or remained inside the capsules when the ME-alachlor(C) formulation was applied. Greater amounts of alachlor were leached through a silty clay loam after EC-alachlor application compared to the three ME-alachlor formulations. Biologically available alachlor was not detected below 15 or 10 cm after application of EC- and ME-alachlor formulations, respectively. All alachlor formulations applied alone or in mixture with atrazine showed similar field persistence. Biologically available alachlor was not detected in the 0- to 10-cm soil depth 30 d after their application. All alachlor formulations applied alone gave excellent control of redroot pigweed and black nightshade, but only partial control of jimsonweed. None of the herbicide treatments showed any detrimental effect on corn, and all of them increased corn yield to the level of weed-free control.