Browsing by Author "Reichard, Nicholas"

Now showing 1 - 2 of 2

Occurrence and Characterization of Kochia (Kochia scoparia) Accessions with Resistance to Glyphosate in Montana
(2014-01) Kuman, Vipan; Jha, Prashant; Reichard, Nicholas
Herbicide-resistant kochia is an increasing concern for growers in the northwestern United States. Four suspected glyphosate-resistant (Gly-R) kochia accessions (referred to as GIL01, JOP01, CHES01, and CHES02) collected in fall 2012 from four different chemical-fallow fields in northern Montana were evaluated. The objectives were to confirm and characterize the level of glyphosate resistance in kochia accessions relative to a glyphosate-susceptible (Gly-S) accession and evaluate the effectiveness of various POST herbicides for Gly-R kochia control. Whole-plant dose–response experiments indicated that the four Gly-R kochia accessions had 7.1- to 11-fold levels of resistance relative to the Gly-S accession on the basis of percent control ratings (I50 values). On the basis of shoot dry weight response (GR50 values), the four Gly-R kochia accessions exhibited resistance index (R/S) ratios ranging from 4.6 to 8.1. In a separate study, the two tested Gly-R accessions (GIL01 and JOP01) showed differential response (control and shoot dry weight reduction) to various POST herbicides 21 d after application (DAA). Paraquat, paraquat þ linuron, carfentrazone þ 2,4-D, saflufenacil alone or with 2,4-D, and bromoxynil þ fluroxypyr effectively controlled (99 to 100%) and reduced shoot dry weight (88 to 92%) of the GIL01 accession, consistent with the Gly-S kochia accession; however, bromoxynilþMCPA and bromoxynilþpyrasulfotole provided 76% control and 83% shoot dry weight reduction of the GIL01 accession and were lower compared with the Gly-S accession. The JOP01 accession exhibited lower control or shoot dry weight reduction to all herbicides tested, except dicamba, diflufenzopyr þ dicamba þ 2,4-D, paraquat þ linuron, and bromoxynil þ pyrasulfotole, compared with the Gly-S or GIL01 population. Furthermore, paraquat þlinuron was the only treatment with 90% control and shoot dry weight reduction of the JOP01 kochia plants. Among all POST herbicides tested, glufosinate was the least effective on kochia. This research confirms the first evolution of Gly-R kochia in Montana. Future research will investigate the mechanism of glyphosate resistance, inheritance, ecological fitness, and alternative strategies for management of Gly-R kochia. Nomenclature: 2,4-D; bromoxynil; carfentrazone; dicamba; diflufenzopyr; fluroxypyr; glufosinate; glyphosate; linuron; MCPA; paraquat; pyrasulfotole; saflufenacil; kochia, Kochia scoparia (L.) Schrad. Key words: Glyphosate resistance, postemergence herbicides, resistance management.
Tank Mixing Pendimethalin with Pyroxasulfone and Chloroacetamide Herbicides Enhances In-Season Residual Weed Control in Corn
(2015-05) Jha, Prashant; Kumar, Vipan; Garcia, Josefina; Reichard, Nicholas
Kochia, common lambsquarters, and wild buckwheat are major problem weeds in glyphosate-resistant corn production in the northern Great Plains of the United States. Field research was conducted in 2011 and 2012 near Huntley, MT to investigate effective PRE herbicides applied alone or in premixes with or without tank-mixed pendimethalin for extended in-season residual control of the selected broadleaf weeds in glyphosate-resistant corn. Control of kochia, common lambsquarters, and wild buckwheat with recently registered herbicide premixes, including saflufenacil + dimethenamid-P and S-metolachlor + mesotrione, was as high as 95 and 90% at 21 and 63 d after treatment (DAT), and mostly similar to the standard atrazine treatment. Residual control of common lambsquarters and wild buckwheat from pyroxasulfone was higher at 298 compared with 149 g ai haâˆ’1 rate. Pyroxasulfone and other chloroacetamide herbicides (acetochlor or dimethenamid-P) applied alone failed to provide greater than 79, 70, and 54% residual control at 21, 35, and 63 DAT, respectively, of the weed species investigated. Residual weed control throughout the growing season was significantly improved with the addition of pendimethalin to pyroxasulfone (149 g haâˆ’1), acetochlor, or dimethenamid-P when compared with any of the three herbicides applied alone. Kochia control by pyroxasulfone, acetochlor, or dimethenamid-P tank mixed with pendimethalin was as high as 94, 92, and 81% at 21, 35, and 63 DAT, respectively. Control of common lambsquarters with the addition of pendimethalin to pyroxasulfone or acetochlor was improved to 94, 89, and 81% at 21, 35, and 63 DAT, respectively. Similarly, wild buckwheat control with acetochlor plus pendimethalin was improved to 87, 85, and 82% at 21, 35, and 63 DAT, respectively. Consistent with the extended in-season (up to 9 wk) residual weed control, pyroxasulfone, acetochlor, or dimethenamid-P treatments when tank mixed with pendimethalin had higher corn yields compared with the herbicides applied alone. The investigation on residual herbicides that provide extended in-season weed control should be continued as an important aspect of glyphosate stewardship and to mitigate the occurrence of glyphosate-resistant weed populations in grower fields.