Master of Science / Agronomy / Johanna A. Dille / Mithila Jugulam / Common lambsquarters (Chenopodium album L.) is an annual broadleaf weed species that competes with more than 40 crop species around the world. A biotype of common lambsquarters in north central KS (DK) was not controlled by a glyphosate application. Plant growth stage and temperature have been related to overall glyphosate efficacy on common lambsquarters. The objectives were to determine the: 1) tolerance of two biotypes of common lambsquarters to glyphosate, 2) efficacy of glyphosate on common lambsquarters at different growth stages, and 3) efficacy of glyphosate on common lambsquarters when grown at different temperatures. Greenhouse dose-response experiments, shikimate accumulation assay, and glyphosate uptake and translocation experiments were conducted using DK biotype and a known susceptible biotype (RL) of common lambsquarters for comparison. Dose-response results indicated elevated tolerance of the DK biotype to glyphosate based on the GR₅₀ (a dose causing 50% biomass reduction) values (373 g ae/ha for RL vs. 552 g ae/ha for DK). Similarly, the DK biotype accumulated slightly less shikimate in the leaf discs compared to the RL biotype. Minimal differences were observed in ¹⁴C-glyphosate uptake and translocation between the two biotypes. Greenhouse-grown common lambsquarters were treated with glyphosate at a field dose (1x) of 840 g ae/ha when they were 5-7, 10-12, 15-17 or 19-21 cm tall. Common lambsquarters were also grown in growth chambers for 1 wk maintained at d/n temperatures of 25/15, 32.5/22.5, or 40/30 C and then treated with 0-, 0.125-, 0.25-, 0.5-, 0.75, 1.0-, and 2.0-x rates of glyphosate at 8-10 cm tall. Visual injury was recorded 1 WAT and biomass was determined 2 WAT. Common lambsquarters plants treated at 5-7 cm were more susceptible than larger plants to glyphosate. Furthermore, plants were more susceptible to glyphosate when grown under lower temperatures of 25/15 C than higher temperatures. Overall, these results suggest that the DK biotype of common lambsquarters appears to have elevated tolerance to glyphosate. Additionally, glyphosate should be applied early in the season when plants are small and temperatures are cooler for optimal control of common lambsquarters.

Herbicide combinations are common in corn production in the United States to control broadleaf and grass weed species. Studies were conducted in 1995 and 1996 to: (1) investigate the interactions of 2,4-D and dicamba with halosulfuron-methyl on common lambsquarters and common ragweed control in corn, (2) determine the effect of 2,4-D on the foliar absorption, translocation, and metabolism of 14C halosulfuron-methyl in common lambsquarters, (3) examine the interactions of 2,4-D, dicamba, and ALS-inhibitor herbicides with rimsulfuron plus thifensulfuron-methyl (RT) and with sethoxydim on giant foxtail, common ragweed, and common lambsquarters control in corn. Combinations of halosulfuron-methyl with 2,4-D or dicamba were generally additive in their effects on common lambsquarters and common ragweed control, and were occasionally synergistic on common lambsquarters. Synergistic herbicide interactions in the greenhouse were observed with 2,4-D (17 g/ha ) and halosulfuron-methyl (18 g/ha) and 2,4-D (70 g/ha ) in combination with halosulfuron-methyl at 4.5 and 36 g/ha, respectively. Absorption and translocation of 14C-halosulfuron-methyl were not influenced by the addition of 2,4-D, with absorption increasing with time. Three unknown halosulfuron-methyl metabolites (M1, M2, and M3) with Rf values of 0.0, 0.97, and 0.94, respectively, were isolated. The addition of 2,4-D increased the level of M3 at the 18 g/ha halosulfuron-methyl rate, which may contribute to common lambsquarters phytotoxicity. Antagonism on giant foxtail control was observed with all combinations of RT and 2,4-D. Tank mixtures of RT with flumetsulam plus clopyralid plus 2,4-D, atrazine, 2,4-D, and dicamba plus atrazine controlled giant foxtail £ 78% 65 (DAT). RT mixed with flumetsulam plus clopyralid plus 2,4-D injured corn 26%, and yields were reduced 34% when compared to RT alone. Giant foxtail control from sethoxydim tank-mixed with bentazon plus atrazine with urea ammonium nitrate (UAN), or with ALS-inhibiting herbicides except halosulfuron-methyl in combination with 2,4-D was 24% lower when averaged over treatments. Yields of sethoxydim-resistant (SR) corn treated with sethoxydim mixed with combinations of sulfonylurea herbicides plus 2,4-D were low, with the exception of the combination halosulfuron-methyl with sethoxydim and 2,4-D. These studies indicate that thoroughly understanding postemergence (POST) corn herbicide tank mixtures is crucial for effective weed management. / Ph. D.

The purpose of this research was to evaluate a common lambsquarters (Chenopodium album) collection from Westmoreland County, Virginia, which exhibited a differential response to glyphosate treatments as compared to most other common lambsquarters. Plants from this site that survived glyphosate applications were collected in both 2002 and 2004. Greenhouse studies were conducted on F1, F2, and F3 progeny from this collection and compared to a wild type collection from Montgomery County, Virginia. Evaluations were conducted on these plants treated with a range of glyphosate rates. F1 progeny of the Westmoreland plants from both 2002 and 2004 collections showed reduced response to glyphosate relative to the Montgomery collection. Vigor reduction of F1 progeny from three 2004 Westmoreland source plants with 0.84 kg ae/ha of glyphosate ranged from 66 to 85% at 28 days after treatment (DAT), compared to 89% for the Montgomery collection. Evaluation of four Westmoreland F2 common lambsquarters lines derived from 2002 collections indicated significant differences in glyphosate sensitivity. Fifteen F2 lines were generated from 2004 collections from each of three Westmoreland source plants and from the Montgomery source. For the least sensitive Westmoreland source, vigor reduction ranged from only 24 to 36% across F2 lines in response to 1.68 kg/ha of glyphosate at 28 DAT, relative to 55 to 100% for the Montgomery source. I50 estimates for fresh weight reduction were 0.91 and 0.32 kg/ha, for these sources, respectively. Sequential treatments of 0.42, 1.26, and 1.68 kg/ha applied at three-week intervals to the least susceptible 2004 Westmoreland F2 line resulted in only 37% vigor reduction and no mortality among 360 treated plants. Growth chamber studies were also conducted on the F2 progeny of these sources to determine if differential growth responses occur in noncompetitive environments and in the absence of glyphosate treatment. Generally, few differences were observed among the Westmoreland and Montgomery collections in growth parameters including height, leaf number, leaf area, leaf size, shoot weight, and reproductive output. However, significant differences were observed with regard to root weight, root length, and root density. In germination studies, it was determined that the Montgomery source had significantly faster and greater seed germination than the Westmoreland source. The susceptibility of F3 seedlings to glyphosate varied significantly with respect to F2 parent line and glyphosate rate. Mortality of 100% was observed in F3 seedlings from the Montgomery source in response to the 3.36 kg ae/ha glyphosate rate, while no mortality was observed in Westmoreland F3 seedlings in response to this glyphosate rate. / Master of Science

The aim of the present diploma thesis is to widen knowledge of the chemical regulation of weeds in row crops. To establish the effectiveness of herbicides, we set up a small lot at a carefully chosen spot in the potato-growing region near Strakonice. We conducted a comparison of the effects of three herbicide combinations on two potato varieties (Red Anna, Laura). Two combinations proved pre-emergent (Afalon 45 SC+Command 36 SC; Sencor 70 WG+Command 36 SC), one post-emergent (Titus 25 WG). Subsequently, we evaluated economic costs on weeds regulation and suggested preliminary measures to be taken.

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