Abstract

Weed management programs are an essential component of rice (Oryza sativa L.) production in Mississippi. Herbicides will continue to be a major component in most integrated weed management systems in rice and other crops. Weeds developing resistance to herbicide continue to be a problem in Mississippi agriculture. A greenhouse study was conducted in 2019 and 2020 at the Delta Research and Extension Center, in Stoneville, Mississippi, to evaluate barnyardgrass resistance to Stam M4 (propanil), Facet (quinclorac), Clincher (cyhalofop), Roundup formulations (glyphosate), Newpath (imazethapyr), Regiment (bispyribac), and Loyant (florpyauxifen-benzyl) in Mississippi rice fields. Forty-six random barnyardgrass accessions from various Counties of Mississippi rice fields were collected in 2018. The number of barnyardgrass plants surviving from each herbicide application was recorded four-weeks after application to determine the percentage of barnyardgrass-resistant for each population and for each herbicide application. The high level of barnyardgrass survival from Loyant application indicate that Loyant alone is not be able to control barnyardgrass. The suspected barnyardgrass-resistant plants (survived plants) from each herbicide application except for Loyant were transplanted in a bigger pot for seed production. The seed (F1) was harvested for the next step of testing in 2020 to investigate the level of barnyardgrass seedling (from survived plants in 2019) response to different rates (1/2 X, 1X, 2X, and 4X) of Propanil, Facet, Clincher, Glyphosate, Newpath, and Regiment (does response). Four suspected herbicide-resistant (highest level) barnyardgrass populations from Propanil, Facet, Clincher, Regiment, Newpath, and Glyphosate were selected for does response. The results indicate that the F1 population of suspected herbicide-resistant barnyardgrass from Desoto-1 County is resistant to Propanil, Newpath, Clincher, and Regiment (multiple resistance) and the F1 population of suspected herbicide-resistant barnyardgrass from Washington-1 County is resistance to Propanil, Newpath, Clincher, Regiment, and Glyphosate (multiple resistance).

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