Biology and control of yellow and knotroot Foxtail

Abstract

Setaria pumila Roem. & Schult. (1817 and Setaria parviflora (Poir.) Kerguelen, respectively known as yellow and knotroot foxtail, are two common species infesting turfgrass, pastures, roadsides, and some cropping systems in the United States with few herbicidal control options. Research was conducted in greenhouse and field to evaluate the response of yellow and knotroot foxtail to different herbicides. Results of the greenhouse studies showed that all the treatments control yellow foxtail >87% in a single post-application. In contrast, only sulfentrazone alone controlled knotroot foxtail >90% resulting in a complete reduction of above-ground biomass. Sethoxydim (520 g ha-1), metribuzin, and imazaquin controlled knotroot foxtail >70% at 28 DAA. Field studies were more variable. Our results indicate that knotroot foxtail is more difficult to control, making differentiation of these two species important before herbicides are applied. Yellow and knotroot share morphological characteristics and are often misidentified, which may result in improper herbicide selection. The criteria to differentiate yellow and knotroot appears late, long after identification is required for weeds management in turfgrass. Research was conducted at the herbicide resistance diagnostics laboratory at Auburn University in Alabama to differentiate yellow and knotroot foxtail beyond morphological characteristics using DNA barcoding. Yellow foxtail closely resembles knotroot foxtail, and standard measurements of culm lengths, blade widths, panicle, and floret lengths often overlap between species making identification a challenge. No single character taken on its own is sufficient for distinguishing the two species. It demands close evaluation of multiple characters at once. Sanger sequencing results of rbcl, ITS, and matK regions demonstrate the presence of different single nucleotide polymorphisms in the sequenced regions that can differentiate yellow and knotroot foxtail. The Neighbor-joining phylogenies using concatenate sequence of ITS, rbcl and matk demonstrate a close evolutionary relationship between yellow and knotroot foxtail. The bootstrap analyses support a monophyletic origin of yellow and knotroot foxtail (i.e. 90%). All the foxtail biotypes collected were clustered into their respective clades. Some foxtail biotypes, classified as unknown, were clustered either on yellow or knotroot foxtail using, making those barcodes relevant for differentiating the foxtail at early stages.