Selectivity, Movement, and Persistence of Soil-Incorporated Herbicides in Carrot Plantings

Abstract

The comparative performances of several herbicides incorporated 2.5 cm deep and unincorporated in furrow-irrigated soil were studied in four field experiments. Among eight herbicides evaluated,a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) was the most effective herbicide and controlled redroot pigweed (Amaranthus retroflexusL.), Palmer amaranth (Amaranthus palmeriS. Wats.), common purslane (Portulaca oleraceaL.), and barnyardgrass (Echinochloa crusgalli(L.) Beauv.) when incorporated, without reduction of yield in carrots (Daucus carotaL., var.saliva, cv. Long Imperator). Trifluralin andO,O-diisopropyl phosphorodithioateSester withN-(2-mercaptoethyl)benzenesulfonamide (bensulide) gave consistently good results in all years although soil temperatures and evaporative losses of water were variable. Bioassays indicated and gas-liquid chromatographic (hereinafter referred to as GLC) assays confirmed that rainfall moved bensulide and trifluralin 2.5 cm downward in soil, and that dimethyl tetrachloroterephthalate (DCPA) was not moved below the original depth of incorporation in soil. GLC assays were most sensitive but generally agreed with bioassays of trifluralin-treated soils. Under high temperatures, infrequent rainfall, and furrow irrigation, the half-life of DCPA and trifluralin activities was 3 weeks, with no biological activity after 7 months. The half-life of bensulide activity was 6 months, with no biological activity after 22 months.

Persistence of terbacil and trifluralin under different soil and climatic conditions

“…The results of this study conform with findings of some other workers as the time required for the disappearance of phytotoxic residues in most of our trials is comparable to those obtained by Allott (1970) and Gardiner et al (1967) for terbacil and by Menges & Hubbard (1970), Probst et ai. (1967 and Schweizer & Holstun (1966) for trifluralin.…”

“…Both trifluralin and terbacil are known to have a long persistence in the soil, but the published reports show marked variability in the time required for their disappearance below phytotoxic levels. The concentration of trifluralin decreased to 10-15% of that applied within a half to one year (Probst et al, 1967) and toxic residues from the recommended rates disappeared within 5-7 months (Schweizer & Holstun, 1966;Menges & Hubbard, 1970). However, some other workers found that trifluralin persisted for more than a year in their trials (Rahman & Ashford, 1973;Wiese et al, 1969).…”

Response of Onion (Allium cepa) to Annual Weeds and Postemergence Herbicides

“…Onion competes poorly with weeds and is susceptible to most herbicides (9,11). Many summer annual weeds in vegetables have been controlled selectively with bensulide [O,O-diisopropyl phosphorodithioate S -ester with N -(2 -mercaptoethyl) benzenesulfonamide] and DCPA (dimethyl tetrachloroterephthalate) (10,11), but winter annuals including London rocket, common sunflower, ragweed parthenium, and annual sowthistle are resistant to these soil-applied herbicides.…”

Effect of Temperature, Moisture, and Soil Texture on DCPA Degradation

“…There has been little direct research on the effect of soil types on the DCPA degradation. However, many reports on the minimal movement of DCPA in the soil profile suggest that there may be a high chance of DCPA adsorption to soil, particularly organic matter or clay (Hurto and Turgeon, 1979;Mazur et al, 1969;Menges and Hubbard, 1970;Miller et al, 1978). If we assume high adsorption of DCPA to clay, a slower degradation rate can be expected from a soil with a higher clay content, leaving DCPA less available for microorganism decomposition.…”

“…DCPA, introduced in 1959, has been used in a wide range of crops including turf (Weed Science Society of America, 1983). Many studies have been conducted to examine the performance of DCPA under different cropping conditions, reporting effective suppression of annual weed germination by DCPA (Menges and Hubbard, 1970;Miller et al, 1978;. However, inconsistent control in comparison to other preemergence herbicides was repmted by Johnson (1976).…”