Conventional lentil, because it is relatively noncompetitive, requires effective weed control. In conventional lentil, metribuzin should be applied by the four-node stage to avoid crop injury. This is earlier than the critical period of weed control (CPWC) of lentil, which is between the five- and 10-node stage. However, imidazolinone herbicides potentially can be applied later in imidazolinone-resistant lentil, which might allow lentil to be kept weed-free for the CPWC. The objective of this experiment was to determine the best herbicide choice and application timing necessary to achieve the CPWC in lentil. To do this we tested herbicides differing in efficacy and residual control. The herbicides imazethapyr/imazamox, imazamox, and metribuzin sethoxydim were applied at the two- and six-node lentil stage. Of the three herbicide treatments, metribuzin sethoxydim resulted in grain yield that was on average 31% lower than the other herbicides. This occurred because of greater broadleaf biomass (composed primarily of wild mustard) in lentils treated with these herbicides regardless of application timing. Because of this, the CPWC was not attained with metribuzin sethoxydim. Late applications of imazethapyr/imazamox or imazamox resulted in grain yields 30% higher than with early application of these herbicides. Early applications of the imidazolinone herbicides gave poor control of grass weeds (wild oat and green foxtail), but late applications resulted in grass weed control equivalent to metribuzin sethoxydim. Imazethapyr/imazamox or imazamox should be applied at the five- to six-node stage of lentil to achieve the CPWC.

Nomenclature: Imazamox; imazethapyr; metribuzin; sethoxydim; green foxtail, Setaria viridis (L.) Beauv.; wild mustard, Sinapis arvensis L.; wild oat, Avena fatua L.; lentil, Lens culinaris Medik. ‘CDC Impact’.