Selectivity of Nitrofen among Rape, Redroot Pigweed, and Green Foxtail

Abstract

The selectivity of 2,4-dichlorophenylp-nitrophenyl ether (nitrofen) among rape (Brassica campestrisL., var. Echo) and two weed species, redroot pigweed (Amaranthus retroflexusL.) and green foxtail (Setaria viridis(L.) Beauv.), was determined quantitatively by a replicated dosage-response experiment. On an ED₅₀basis, green foxtail and redroot pigweed were, respectively, 5.8 and 63.3 times more susceptible than rape. Selectivity was divided into three parameters; viz., differential spray retention, differential penetration, and differential effects within the plant. Differences in retention were measured with the use of a water-soluble dye, while differences in penetration were determined with¹⁴C-labelled nitrofen. Spray retention on green foxtail was 66% of that on the rape and 64% as much nitrofen penetrated redroot pigweed as penetrated rape. Under the conditions of these tests it was estimated that green foxtail and redroot pigweed were, respectively, 9 and 99 times more susceptible to nitrofen than was rape.