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United States Department of Agriculture

Agricultural Research Service

Title: Onion weed control: 2003 transplanted onion weed control trial

Authors
item Shrefler, J.W. - OSU, LANE, OK
item Webber, Charles

Submitted to: Oklahoma Agriculture Experiment Station Departmental Publication
Publication Type: Experiment Station
Publication Acceptance Date: January 22, 2004
Publication Date: February 2, 2004
Citation: Shrefler, J., Webber III, C.L. 2004. Onion weed control: 2003 transplanted onion weed control trial. In: Brandenberger, L., Wells, L., editors. 2003 Vegetable Weed Control Studies. Oklahoma State University, Division of Agricultural Sciences and Natural Resources, Department of Horticulture and Landscape Architecture. Stillwater, OK. MP-164. p. 60-62.

Interpretive Summary: Fresh market onion production is increasing in Arkansas, Oklahoma, and north Texas. Although mechanical weed control can successfully control weeds between rows, producers need reliable methods for controlling the weeds within the crop row between the onions. Effective weed control is essential in sweet onion production because even a small amount of weed competition can result in large reductions in onion yields and quality. Field research was conducted in southeast Oklahoma (Lane, OK) to determine the effectiveness and safety of twelve weed control treatments on onion yield and quality. Greenhouse-grown yellow granex onions were transplanted to the field on March 26 into raised beds on 6-ft centers in two rows, 3-ft apart, and 6 inches between onions within rows. Weed control treatments included two application dates (April 4 and May 19), three herbicides (pendimethalin, oxyfluorfen, and dimethenamid), a weedy-check (no weed control), and a hand-hoed treatment. Dimethenamid is not yet registered for use in onions, but has potential as an effective and safe herbicide for use in onions. Total onion yields ranged from 6,630 lb/a (weedy-check) to 10,130 lb/ac (dimethenamid, 1.5 lb/a + pendimethalin, 0.4125 lb/a, applied on April 4). Weeds reduced total onion yields to the equivalent of the weedy-check, the lowest yielding treatment, whenever herbicides were not applied at the first application date. Weed control treatments also affected the distribution of onions within the three size classes (less than 2 inch diameter, 2 to 3 inch diameter, and 3 to 4 inch diameter). Dimethenamid, 1.5 lb/a + pendimethalin, 0.4125 lb/a applied at the first application date produced the greatest total onion yields (10,130 lb/a), with the greatest yield advantage seen in the largest onion size (3 to 4 inch diameter). Only treatments including dimethenamid provided sufficient yellow nutsedge (Cyperus esculentus) control, and dimethenamid applied at 1.5 lb/a produced greater nutsedge control and onions yields than dimethenamid applied at 0.75 lb/a. Smooth groundcherry (Physalis subglabrata) control was excellent with oxyfluorfen (0.25 or 0.5 lb/a), good with dimethenamid (0.75 or 1.5 lb/a), and less than good with pendimethalin (0.4125 or 0.825 lb/a). Pendimethalin produced partial Pennsylvania smartweed (Polygonum pensylvanicun) control, which increased as the rate increased from 0.4125lb to 0.825 lb/a, whereas oxyfluorfen (0.25 or 0.5 lb/a) was very effective. Dimethenamid at 1.5 lb/a applied with pendimethalin at 0.4125 lb/a provide the best overall weed control and significantly greater onion yields. Although dimethenamid is not currently registered for use in onions, this research demonstrated its excellent potential for weed control in onions, especially in controlling yellow nutsedge. The research also verified the importance of early weed control in onions.

Technical Abstract: Interest in fresh market onion production is increasing in Arkansas, Oklahoma, and north Texas. Effective weed control is essential in sweet onion production because even a small amount of weed competition can result in large reductions in onion yields and quality. Although mechanical weed control can successfully control weeds between rows, producers need reliable methods for controlling the weeds within the crop row between the onions. Field research was conducted in southeast Oklahoma (Lane, OK) to determine the efficacy of twelve weed control treatments on onion yield and quality. Greenhouse-grown yellow granex onions were transplanted to the field on March 26 into raised beds on 6-ft centers in two rows, 3-ft apart, and 6 inches between onions within rows. Weed control treatments included two application dates (April 4 and May 19), three herbicides (pendimethalin, oxyfluorfen, and dimethenamid), a weedy-check (no weed control), and a hand-hoed treatment. Total onion yields ranged from 6,630 lb/a (weedy-check) to 10,130 lb/ac (dimethenamid, 1.5 lb/a + pendimethalin, 0.4125 lb/a, applied on April 4). Weeds reduced total onion yields to the equivalent of the weedy-check, the lowest yielding treatment, whenever herbicides were not applied at the first application date. Weed control treatments also affected the distribution of onions within the three size classes (A = less than 2 inch diameter, B = 2 to 3 inch diameter, and C = 3 to 4 inch diameter). Dimethenamid, 1.5 lb/a + pendimethalin, 0.4125 lb/a applied at the first application date produced the greatest total onion yields (10,130 lb/a), with the greatest yield advantage seen in the largest onion size (3 to 4 inch diameter). Only treatments including dimethenamid provided sufficient yellow nutsedge (Cyperus esculentus) control, and dimethenamid applied at 1.5 lb/a produced greater nutsedge control and onions yields than dimethenamid applied at 0.75 lb/a. Smooth groundcherry (Physalis subglabrata ) control was excellent with oxyfluorfen (0.25 or 0.5 lb/a), good with dimethenamid (0.75 or 1.5 lb/a), and less than good with pendimethalin (0.4125 or 0.825 lb/a). Pendimethalin produced partial Pennsylvania smartweed (Polygonum pensylvanicun) control, which increased as the rate increased from 0.4125lb to 0.825 lb/a, whereas oxyfluorfen (0.25 or 0.5 lb/a) was very effective. Dimethenamid at 1.5 lb/a applied with pendimethalin at 0.4125 lb/a provide the best overall weed control and significantly greater onion yields. Although dimethenamid is not currently registered for use in onions, this research demonstrated its excellent potential for weed control in onions, especially in controlling yellow nutsedge. The research also verified the importance of early weed control in onions.

Last Modified: 12/18/2014
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