A study was conducted in 1995 and 1996 to determine the effect of soybean planting date, tillage level, and glyphosate application on sicklepod control and seed production. Soybean was planted in April, May, June, and July into conventional and no-till seedbeds. Herbicide programs evaluated were metribuzin plus chlorimuron preemergence (PRE) followed by (fb) chlorimuron postemergence (POST) (standard program [STD]), metribuzin plus chlorimuron PRE fb glyphosate POST as-needed, and glyphosate POST as-needed. Control was similar across planting dates in both years with slight variations due to weather. The July planting date had the lowest total sicklepod seed production over the 2-yr study. Sicklepod control was better in conventional tillage, but soybean yields were greater in no-till. Herbicide programs that included glyphosate provided greater sicklepod control, lower sicklepod seed production, and higher soybean yields than the STD. Use of glyphosate in combination with later planting dates, especially July, has the potential to prevent sicklepod seed accumulation in the soil while maintaining yields in a dryland soybean production system.
Nomenclature: Chlorimuron; glyphosate; metribuzin; sicklepod, Senna obtusifolia (L.) Irwin and Barnaby #3 CASOB; soybean, Glycine max (L.) Merr.
Additional index words: CASOB, no-till, planting date, Roundup Ready soybean, sicklepod seedbank.
Abbreviations: fb, followed by; POST, postemergence; PRE, preemergence; STD, standard program; WAE, weeks after emergence.
