Submitted to: Arkansas Crop Protection Association Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: November 22, 2004
Publication Date: November 29, 2004
Citation: Burgos, N.R., Shivrain, V.K., Gealy, D.R., Black, H.L. 2004. Planting date matters in Clearfield rice outcrossing [abstract]. Arkansas Crop Protection Association Proceedings. 8:7. Technical Abstract: Clearfield rice, which is resistant to the imidazolinone herbicide Newpath(imazethapyr), provides the best technology thus far for red rice management. Its use is rapidly increasing in the southern U.S. where red rice is a problem. Sustainability of this technology depends on the extent by which the development of herbicide-resistant red rice can be mitigated. Herbicide-resistant red rice could ensue from 1) gene flow between Clearfield rice and red rice and 2) selection pressure from Newpath herbicide. While selection pressure would take time, successful gene transfer from rice to red rice could happen after one season if synchronization in flowering occurs. Several factors contribute to the overlap of flowering between cultivated and weedy species. This research aimed to evaluate the effect of planting date on the synchronization of flowering between rice and red rice. CL121, CL161, and Stuttgart strawhull red rice were planted at the Rice Research and Extension Center (RREC), Stuttgart, AR in 2002 to 2004 at 6 timings starting from mid-April up to about the third week of May at weekly intervals. Of these two cultivars, CL161 is more recent and widely used. The Clearfield cultivars were drill-planted in 9-row plots, 20 ft long, with Clearfield rice planted in the outermost row and red rice planted every other row. Each rice cultivar was replicated four times in each planting date. Early planted rice and red rice took longer to flower than later planted ones. CL121 flowered earlier than CL161 and therefore had more overlap in flowering with strawhull red rice in any planting date. The earliest planting date resulted in the most overlap in flowering between either cultivars of Clearfield rice and red rice. Preliminary tests of seed samples also showed more resistant red rice progenies from the earliest planted crop compared to later plantings. In locations similar to Stuttgart, it is advisable to schedule planting of CL161 at least by the end of April to minimize the potential for outcrossing with strawhull red rice.