Barnyardgrass control in conventional and Clearfield rice grown under intermittent flooding

In the mid-southern United States, rice (Oryza sativa L.) is flooded primarily to suppress weed germination and growth. Two experiments were conducted to determine whether herbicide performance in conventional or Clearfield rice weed control programs was affected by intermittent flooding. The effects of flooding and herbicide program on barnyardgrass [Echinochloa crus-galli (L.) P. Beauv] control, rice grain yield, and water applied were investigated at the Delta Research and Extension Center in Stoneville, MS, on Sharkey clay (very fine, smectitic, thermic Chromic Epiaquert). For herbicides commonly applied in conventional (clomazone, quinclorac, pendimethalin, thiobencarb, fenoxaprop-ethyl, cyhalofop-butyl, and bisypriboac sodium) or Clearfield rice weed control programs (imazethapyr plus bispyribac-sodium followed by imazethapyr, imazamox or bispyribac-sodium), intermittent flooding had no adverse effect on barnyardgrass control relative to a continuous flood. Moreover, initiating irrigation when the perched water table drops to 8 inches below the soil surface had no effect on rice grain yield and reduced water applied by 51%. Mid-southern US rice producers can capture the water-saving benefits of intermittent flooding while having no adverse effects on herbicide activity or crop productivity in conventional and Clearfield systems.