Effect of Soil Incorporation on Selectivity, Movement, and Persistence of Herbicides in Onion Plantings1

Abstract

The performances of 3 herbicides non-incorporated and incorporated to depths of 3.8 and 7.6 cm in sandy loam were studied in onion plantings in 3 field experiments. Herbicidal activity of 4.5 kg/ha of O,Odiisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide (bensulide) was outstanding and controlled redroot pigweed (Amaranthus retroflexus L.), Palmer amaranth (Amaranthus palmen S. Wats.), common purslane (Portulaca oleracea L.), and barnyardgrass [Echinochloa crusgalli (L.) Beauv.] without reducing yields in onions (Allium cepa L., ‘Yellow Granex’). The herbicide was more efficient when soil-incorporated. Bensulide failed to control ridgeseed spurge (Euphorbia glyptosperma Engelm.) and London rocket (Sisymbrium irio L.). 2-Chloro-N-isopropylacetanilide (propachlor) controlled ridgeseed spurge without reducing the yield of onions. Soil-incorporated dimethyl tetra-chloroterephythalate (DCPA) reduced the yield of onions. Laboratory bioassays indicated that regardless of rainfall, bensulide remained within the original zones of incorporation. Persistence of the herbicide increased with soil incorporation and rate of application. Considerable activity persisted for 6 months but only a trace persisted 12 months after 4.5 and 9.0 kg/ha of bensulide were soil incorporated. DCPA and propachlor persisted less than 6 months. Field bioassays agreed with data from laboratory bioassays.