Browsing by Subject "Herbicide"
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Item Effects of row spacing on diseases, herbicide persistence, and qualitative characteristics of peanut(Texas A&M University, 2005-08-29) Besler, Brent AlanField and greenhouse studies were conducted to assess the effects of row-spacing on diseases, weed control, herbicide persistence and plant development in peanut. Tebuconazole, when averaged across cultivars and row spacing, effectively controlled white mold (57%) and rust (58%). Azoxystrobin also controlled white mold (58%) and controlling rust (44%). Both fungicides reduced leaf spot severity in the conventional and twin rows when compared to untreated plots. Twin rows showed a 10% yield increase compared to the conventional planting. Both diclosulam and imazapic, when applied to twin rows at the full and reduced rate, provided better yellow nutsedge control than when applied to the conventional row. Twin rows yielded higher than the conventional rows when averaged across herbicides in one year. All full rate herbicide treatments enhanced yield over the untreated check. Diclosulam and imazapic treated soil sampled 60 DAP adversely affected all four crops. The advantage of planting peanuts in twin rows to reduce diclosulam and imazapic residual concentrations was not apparent. Georgia Green and Tamrun 96 planted in twin rows at three of the four locations in 1999 and 2000 yielded higher than peanuts planted in conventional rows. Yields were comparable to twin-row spacings that had higher plant densities. Georgia Green and Tamrun 96 planted in conventional rows, in most cases, had higher yields than narrow-rows. Measurements for plant diameter, pod distribution, and main stem length were higher with Tamrun 96 at most row spacings and planting densities compared to the respective Georgia Green planting densities and row spacings. Both cultivars when planted in twin or narrow rows at all planting densities did not enhance maturity when sampled late season. Georgia Green and Tamrun 96 when planted in conventional rows had the most pods/plant compared to the narrow and twin row spacing. No clear evidence was found to suggest that peanuts grown in narrow or twin rows increased white mold disease incidence. Grades for Georgia Green were higher than Tamrun 96 when planted in twin rows at the standard planting density. Tamrun 96 in twin rows at the standard planting density had a higher grade than when planted in conventional rows at the low planting density.Item Occurrence and Management of Glyphosate Resistant Amaranthus Weed Species in Central Texas Cotton and Evaluation of Spray Droplet Size Spectra as Affected by Nozzle Design and Herbicide Formulation(2014-08-28) McGinty, Joshua AllanWith the recent confirmation of glyphosate-resistant Amaranthus species in many important agronomic regions of the United States, a study was initiated to identify and document the occurrence of glyphosate resistant common waterhemp in East-central Texas. Accessions of several suspected glyphosate-resistant biotypes of common waterhemp were grown in a greenhouse before receiving rates of glyphosate from 434 to 3468 g ae ha^-1. Dose-response analyses were conducted to provide LD50 values for each accession. LD50 values ranged from 387 to 4549 g ae ha^-1 glyphosate. A study evaluating the efficacy of twelve different weed control programs for common waterhemp and Palmer amaranth control in cotton was conducted in Burleson County, TX in 2012 and 2013. The study was conducted in cotton possessing stacked glyphosate-, glufosinate-, and dicamba-tolerant technologies. Preplant and preemergence treatments included fomesafen, pendimethalin, prometryn, pyrithiobac, S-metolachlor, and trifluralin. These treatments were followed by a variety of early- and mid-postemergence treatments. Preplant and preemergence treatments resulted in 81 to 100% control of Palmer amaranth and common waterhemp with the exception of pyrithiobac, which provided only 29 to 60% control of these species. Following early- and mid-postemergence applications, 92 to 100% control of these species was obtained. Applications of pendimethalin PRE followed by pyrithiobac EPOST and glufosinate MPOST in 2013 provided lower control of both species (92 to 93 %) than all other treatments evaluated in the study 14 days after MPOST applications. With the potential commercialization of synthetic auxin-tolerant crops, there is an increased need for understanding of the influence of spray nozzle design and herbicide formulation on physical spray drift reduction. A study was conducted in a low speed wind tunnel utilizing laser diffraction technology to analyze the droplet size spectra produced by different spray nozzles and herbicide formulations. Nozzles utilizing a pre-orifice design or a combination of pre-orifice and air-inclusion design were observed to produce significantly larger spray droplets than those without these features. Herbicide formulations were shown to have a significant influence on droplet size as well. Different herbicide formulations were observed to decrease the production of drift-prone fine droplets by as much as 64%.Item Response of nesting grassland birds to sand shinnery oak communities treated with tebuthiuron and grazing in eastern New Mexico(Texas Tech University, 2006-05) Smythe, Lindsay Allison; Haukos, David A.; Smith, Loren M.; McIntyre, Nancy E.Many grassland bird species have exhibited population declines during the past three decades. Major components of grassland bird habitat in eastern New Mexico include sand shinnery oak (Quercus havardii) communities, many of which have been subject to unmanaged livestock grazing and other impacts for decades. As a result, these sand shinnery oak communities tend to deviate from the historical grass/shrub vegetation mix in favor of shrubs. These communities are frequently managed with livestock grazing and herbicide application for shrub control. These techniques can be used for potential restoration of historical community structure. However, responses of spring migrating and nesting grassland birds to these management practices in shinnery oak communities are not well understood because of variation in species response. Additionally, most of the research in these communities has focused on game species. My study objectives, in the context of restoring shinnery oak communities, were to: 1) determine if tebuthiuron herbicide application or short-duration grazing had negative impacts on avian community structure (i.e., density, species richness, diversity, and evenness), 2) determine if the vegetation changes caused by tebuthiuron application and short-duration grazing negatively impacted avian reproduction (nest density and success), and 3) develop recommendations to benefit grassland birds when using herbicides and livestock grazing in sand shinnery oak communities. My study site in eastern New Mexico consisted of 1,040 ha divided into 16 plots of 65 ha each. The plots consisted of 2 treatments arranged in 4 combinations: tebuthiuron with grazing; tebuthiuron without grazing; no tebuthiuron with grazing; and a control of no tebuthiuron or current grazing. I performed biweekly point transects on these plots from February through July 2004 and 2005. Density of bird species was estimated using program DISTANCE. I also searched 4-ha subplots in each treatment plot for nests from April-June 2004 and 2005. I monitored nests to estimate daily survival rates and recorded vertical density and overhead cover measurements at each nest site to determine if vegetation structure affected nest daily survival or success. In 2005, I placed 64 artificial nests to supplement information from real nests. This study occurred over years of highly variable precipitation: 2003 represented the end of a 15-year drought with below-average precipitation, but during 2004, the area received 3 times the average amount of precipitation, the second highest amount ever recorded in the region. The above-average precipitation affected habitat conditions and likely impacted my results, but precipitation returned to near average in 2005, so these conditions may not persist. Density of all avian species did not differ between grazed and ungrazed plots. Tebuthiuron-treated plots had a higher density of all species than untreated plots. There was a higher density of all species during spring 2005 than 2004 but density was similar during the breeding season of both years. These trends were predominantly influenced by Cassin’s sparrows (Aimophila cassinii) and, in 2005, grasshopper sparrows (Ammodramus savannarum). Tebuthiuron-treated plots had a higher density of Cassin’s sparrows in both years. Grasshopper sparrows were not recorded in 2004 but were present in greater numbers on tebuthiuron-treated plots in 2005. The density of resident species (meadowlarks [Sturnella spp.] and loggerhead shrikes [Lanius ludovicianus]) exhibited little response to tebuthiuron or grazing treatments. Species richness was not affected by tebuthiuron or grazing, but was higher in the spring of 2005 than 2004 because of greater numbers of migratory sparrows. Decreases in both evenness and diversity in 2005 compared to 2004 were influenced by large flocks of chestnut-collared longspurs (Calcarius ornatus) and lark buntings (Calamospiza melanocorys). Diversity was also lower on ungrazed plots in February and March. Nest density of all species was similar among tebuthiuron and grazing treatments but was greater in 2005 than 2004. Nests of migratory species were more numerous in 2005 than 2004, whereas equal numbers of resident species nests were found in both years. Daily nest survival rates were similar between years and between incubation and the nestling periods, but varied among species and treatments. Daily nest survival rates during incubation were 6.3% higher in untreated plots than in tebuthiuron-treated plots, but during the nestling period were 17.3% higher in tebuthiuron-treated plots than in untreated plots. Depredation caused the majority of nest failures. Vertical density of vegetation differed among treatments and was greater in 2005 than 2004 but did not differ between nest sites and associated random points, nor between hatched and failed nests. Vegetation overhead cover did not vary among treatments but was greater in 2005 than 2004 and greater at nest sites than at associated random points. Overhead cover did not differ between nests that hatched and nests that failed. Unusually high rainfall in 2004 likely influenced results, but neither grazing nor tebuthiuron treatment had a substantial impact on resident birds. Migratory birds responded positively to tebuthiuron treatment, but overall density and nest success in this community (regardless of treatment) were extremely low.