Weed Management in Fresh Market Spinach (Spinacia oleracea) withS-metolachlor1

Abstract

Field studies were conducted with fresh market spinach to examine crop tolerance and weed control with S-metolachlor. S-metolachlor was applied preemergence (PRE) at rates of 0.56, 0.72, 1.06, and 1.41 kg/ha and compared with the commercial standard cycloate at 3.4 and 4.5 kg/ha. Spinach was generally tolerant of S-metolachlor at rates up to 1.06 kg/ha on all soil types. S-Metolachlor at 0.56 to 0.72 kg/ha and cycloate at 3.4 kg/ha provided >88% control of common purslane, nettleleaf goosefoot, and shepherd's purse. Control of common chickweed with S-metolachlor at ≥0.56 kg/ha was >80%, whereas cycloate at 3.4 to 4.5 kg/ha was ineffective. Hand-weeding times in plots treated with S-metolachlor at 0.56 and 0.72 kg/ha were similar or lower than hand-weeding times in plots treated with cycloate at 3.4 kg/ha. Greenhouse studies were conducted to compare the relative tolerance of fresh market spinach to S-metolachlor and metolachlor. The GR10 values for S-metolachlor and metolachlor were 1.57 and 2.03 kg/ha, respectively. At rates above 2.2 kg/ha S-metolachlor is less selective in spinach than metolachlor. S-metolachlor is safe for PRE use in fresh market spinach at rates up to 1.06 kg/ha.Nomenclature: Cycloate; metolachlor; S-metolachlor; S-enantiomer; common chickweed, Stellaria media L. Vill. #3 STEME; common purslane, Portulaca oleracea L. # POROL; nettleleaf goosefoot, Chenopodium murale L. # CHEMU; shepherd's-purse, Capsella bursa-pastoris L. Medik # CAPBP; spinach, Spinacia oleracea L. # SPQOL.Additional index words: Herbicide tolerance, weed control, CAPBP, CHEMU, POROL, SPQOL, STEME.Abbreviations: GR10, herbicide concentration required to reduce shoot dry weight by 10%; PRE, preemergence.