Late-Season Weed Control in Glyphosate-Resistant Sugarbeet

Field trials were conducted from 2006 through 2008 to determine the influence of ethofumesate applied at planting followed by dimethenamid-p or s-metolachlor applied to emerged sugarbeet for late-season weed control in glyphosate-resistant sugarbeet. The entire plot area was kept weed-free until mid-June by applying glyphosate at the four- and eight-true-leaf sugarbeet growth stages. Glyphosate was not applied from mid-June until late-July to allow weed growth as a measure of the residual benefit from ethofumesate, dimethenamid-p, and s-metolachlor applied earlier in the growing season. Dimethenamid-p was not as effective as s-metolachlor in reducing weed density in mid-July. Late-season weed suppression from both s-metolachlor and dimethenamid-p benefitted from ethofumesate applied at planting. Dimethenamid-p applied when sugarbeet reached the six-true-leaf growth stage reduced weed density and sugarbeet injury more than earlier applications. The lowest weed density in mid-July was achieved when s-metolachlor was applied at the six- to eight-true-leaf sugarbeet growth stage compared to earlier growth stages. A planting time application of ethofumesate followed by two glyphosate applications plus s-metolachlor at the eight-true-leaf sugarbeet growth stage provided 89%% more weed control in mid-July than glyphosate alone. Suppressing late-season weed development increased sugarbeet root yield 15%% compared with areas not receiving ethofumesate and s-metolachlor.Nomenclature: Clopyralid; desmedipham; dimethenamid-p; ethofumesate; glyphosate; phenmedipham; s-metolachlor; triflusulfuron; common lambsquarters, Chenopodium album L. CHEAL; common puslane, Portulaca oleracea L. POROS; hairy nightshade, Solanum sarrachoides Sendtner SOLSA; redroot pigweed, Amaranthus retroflexus L. AMARE; sugarbeet, Beta vulgaris L. ‘BTS66RR50’.