Turfgrasses that establish quickly can resist weed colonization, and stands with high turf density may reduce weed competition (Busey, 2003). Conversely, stresses that thin turf and expose the soil to sunlight could allow annual weed infestation (Busey, 2003). Common purslane (Portulaca oleracea L.) is a warm-season summer annual weed often found in thin turf, bare soil areas (Matthews et al., 1993), or during turfgrass establishment.
For spring establishment of turfgrass or in thin turf along sidewalks and drives, herbicide control of purslane may be necessary. Labels of many turfgrass herbicides list purslane as a weed species controlled, but limited published research is available on herbicide control of purslane in turf. Several studies in crops other than turfgrass have evaluated purslane control with herbicides, but often only report limited purslane data because it was not the primary target and/or because this weed appeared inconsistently during the studies. Of the research reported, few of the mentioned herbicides are labeled for use in turf, whereas others are not labeled for use in the United States.
Among the products labeled for use in turf, Stacewicz-Sapuncakis et al. (1973) found that purslane was sensitive to the POST herbicide dicamba, but the lethal rate depended on plant age. Postemergence applications of clopyralid resulted in less than 45% control of purslane at harvest of leafy greens (Norsworthy and Smith, 2005), but clopyralid is no longer labeled for use on residential lawns. An evaluation of PRE herbicides for weed control in pumpkin (Cucurbita spp.) found sulfentrazone or dimethenamid resulted in 74% or greater control of purslane 21 d after treatment (Brown and Masiunas, 2002). Bensulide or pronamide applied PRE reduced purslane density in lettuce (Lactaca sativa) by 52% to 98% (Haar and Fennimore, 2003). Preemergence application to control purslane in leafy greens with pendimethalin resulted in greater than 84% control, whereas bensulide plus dimethenamid resulted in less than 78% control (Norsworthy and Smith, 2005).
Among herbicides for controlling purslane that are not labeled in turfgrass or not for use in the United States, POST herbicides nitrofen and oxyfluorfen increase membrane permeability resulting in stomatal closure, membrane disruption, ethylene synthesis, and ultimately leaf abscission in purslane (Gorske and Hopen, 1978). Doohan and Felix (2012) report between 11% and 95% purslane control in green onion with oxyfluorfen applied at three labeled rates. Postemergence treatments with phenmedipham resulted in less than 45% control of purslane at harvest of leafy greens (Norsworthy and Smith, 2005). The PRE herbicides diethatyl, diphenamid, diethatyl plus diphenamid, or S-metolachlor reduced purslane in vegetable crops (Cavero et al., 1996; Norsworthy and Smith, 2005). Imazethapyr applied either PRE or POST in lettuce provided greater than 80% PRE control and greater than 85% POST control of purslane (Dusky and Stall, 1996). The soil fumigant methyl iodide was as effective as methyl bromide in reducing purslane seed germination rates in a laboratory study for the two highest rates tested (Ohr et al., 1996). Because many previously researched herbicides are not currently labeled for use in turf, the objective of our study was to conduct herbicide screens to determine the efficacy of PRE or POST herbicides labeled for turfgrass to control purslane.
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Anonymous2010aBlade® herbicide product label. PBI/Gordon Publication No. 536/1-2010 AP082109. PBI/Gordon Corporation Kansas City MO
Anonymous2010bRifle® herbicide product label. Loveland publication No. 34704-861. Loveland Products Greeley CO
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