ACTIVITY, ADSORPTION, MOBILITY, EFFICACY, AND PERSISTENCE OF ALACHLORAS INFLUENCED BY FORMULATION

Activity, adsorption, mobility, and field persistence of one emulsifia ble 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 concentra tion. EC-alachlor in sand showed the highest activity, while ME-alachl or(L) and ME-alachlor(A), the lowest; the activity of ME-alachlor(C) w as intermediate. In silty clay loam soil, EC-alachlor had the highest activity, while ME-alachlor(L) had the lowest; and ME-alachlor(A) show ed intermediate activity and was similar to that of ME-alachlor(C). Mo re alachlor was adsorbed on the soil or remained encapsulated (not bio logically available) after ME-alachlor(L) and ME-alachor(A) applicatio n compared to EC-alachlor. An intermediate amount of alachlor was adso rbed or remained inside the capsules when the ME-alachlor(C) formulati on was applied. Greater amounts of alachlor were leached through a sil ty clay loam after EC-alachlor application compared to the three ME-al achlor formulations. Biologically available alachlor was not detected below 15 or 10 cm after application of EC- and ME-alachlor formulation s, respectively. All alachlor formulations applied alone or in mixture with atrazine showed similar field persistence. Biologically availabl e alachlor was not detected in the 0- to 10-cm soil depth 30 d after t heir application. All alachlor formulations applied alone gave excelle nt control of redroot pigweed and black nightshade, but only partial c ontrol of jimsonweed. None of the herbicide treatments showed any detr imental effect on corn, and all of them increased corn yield to the le vel of weed-free control.