Evidence that alachlor selectivity in sunflower is based on depth-protection

Abstract

The relative importance of the underground shoot parts (hypocotyl) and roots of sunflower (Helianthus annuus L.) seedlings on the absorption of alachlor [a-chloro-2′,6′-diethyl- N-(methoxymethyl) acetanilide] was studied in a glasshouse experiment. A layer of activated charcoal divided the soil in each pot into a shoot and a root zone. Three herbicide treatments entailed the mixing of alachlor with soil from either the shoot or the root zone, as well as with soil from both zones. Exposure of sunflower roots, or roots plus shoots, to alachlor caused significant reductions in growth. Alachlor, present in the shoot zone only, had little or no effect. Results indicate that alachlor absorption occurred primarily in the root zone, thus implying that selectivity of the herbicide in sunflower may, at least partly, be dependent on depth-protection.