Life Sciences Commons^™

Winter Cover Crop Impacts On Weed Dynamics In Eastern And Central Nebraska, Elizabeth Ann Oys

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

Reducing tillage in cropping systems causes weed management to be dependent on chemical and cultural methods for weed control. Over time, herbicide-resistant weeds have developed due to the continuous selection pressures from herbicides, particularly in the Midwest Corn Belt. Integrated weed management strategies, such as cover crops, can be used to mitigate some of these issues. Cover crops are primarily known for their soil health benefits, but there is evidence that cover crops can suppress weeds. However, less research has been done at the field-scale level to address cover crop impacts on the weed seedbank and aboveground weeds during the …

Herbicide Drift Influence On Amaranthus Spp. Herbicide Resistance Evolution, Bruno Canella Vieira

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

The adverse consequences of herbicide drift towards sensitive crops have been extensively reported in the literature. However, no information is available on the consequences of herbicide drift onto weed species inhabiting boundaries of agricultural fields. Exposure to herbicide drift could be detrimental to long-term weed management as several weed species have evolved herbicide resistance after recurrent selection with low herbicide rates. Despite the herbicide drift exposure and its potential implications on resistance evolution and weed management, resistance prone weed species such as Palmer amaranth (Amaranthus palmeri) and waterhemp (Amaranthus tuberculatus) are often neglected and not properly …

Integrated Management Of Phytophthora Stem And Root Rot Of Soybean And The Effect Of Soil-Applied Herbicides On Seedling Disease Incidence, Vinicius Castelli Garnica

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

Soybean seedling diseases and Phytophthora stem and root rot (PSRR; caused by Phytophthora sojae) are two of the most economically important diseases in North Central U.S. Remarkable differences in disease incidence occur each year, which demonstrate that abiotic and biotic factors must interact for disease onset and development. During 2017 and 2018, field studies were conducted to (i) address the efficacy of seed treatment and genetic resistance for PSRR management on soybean population, canopy coverage (CC), and yield, and (ii) investigate potential interactions between pre-emergence (PRE) herbicides and the incidence of seedling diseases in alluvial soils in Nebraska.

Despite …

Effect Of Soil-Applied Protoporphyrinogen Oxidase Inhibitor Herbicides On Soybean Seedling Disease, Nicholas J. Arneson

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

Seedling disease is one the most economically important diseases of soybean in the United States. It is commonly caused by Fusarium spp., Rhizoctonia solani, Pythium spp., and Phytophthora sojae, alone, or together as a disease complex. Fungicide seed treatments continue to provide the most consistent management of seedling diseases. Soil-applied protoporphyrinogen oxidase (PPO) inhibitor herbicides are used preemergence in soybean production to manage several broadleaf weeds. Applications of PPO-inhibitors can result in phytotoxic injury to soybean when environmental conditions are not favorable for soybean growth. These environmental conditions can favor seedling disease development as well. In this thesis, two …

Influence Of Multispecies Interference Of Common Ragweed (Ambrosia Artemisiifolia L.) And Common Waterhemp (Amaranthus Rudis Sauer) On Soybean [Glycine Max (L.) Merr.] Growth And Yield Under Variable Water Supply In Nebraska, Koffi Badou Jeremie Kouame

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

Common ragweed (Ambrosia artemisiifolia L.) and common waterhemp (Amaranthus rudis Sauer) are two problematic weeds for soybean producers in the United States. Both weeds have evolved resistance to many herbicides, including glyphosate. It is therefore essential to understand how these weeds in mixture impact soybean growth and yield and also how they deplete soil moisture in rainfed and irrigated cropping systems. The objectives of this research were to: (i) understand the influence of variable water supply on soybean yield loss in mixture with ragweed and waterhemp, (ii) quantify the influence of variable water supply on soybean growth in …

The Effect Of Spray Parameters On The Application Of Enlist Duo, Matthew R. Nelson

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

The emergence of new weed control challenges, along with shifts in weed management strategies and cultural practices, has resulted in an increased reliance on chemical weed control in United States (US) cropping systems. As a result, numerous weed species have evolved resistance to herbicides such as glyphosate, thus prompting the development of new weed control systems designed to aid growers in managing resistant weeds. While these new weed control options may give growers additional management options, the high sensitivity of broadleaf crops, fruits, and vegetables to products containing 2,4-D or dicamba increases the potential for herbicide drift resulting from application …

Characterization Of Ground Nozzles For Pesticide Applications, Ryan Henry

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

Pesticide applications are a common component of crop production systems in the United States (US). For row crop systems (e.g. corn, soybean, or wheat), pesticides are applied by ground, aerial, or chemigation methods. The exact method of pesticide delivery is not universally regulated/ prescribed in the US, and the equipment and application technique are largely defined by the individual applicator. A wide variety of choices and decisions must be made by applicators to result in a successful pesticide application. Examples of these choices include proper active ingredient(s), carrier volume and equipment (e.g. nozzle type, spacing, and operating pressure) selection while …

Cover Crop Mixture Diversity And Function, Angela Florence

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

The objective of this study was to evaluate the effect of cover crop mixture diversity on cover crop function. Specifically, this study evaluated the effect of cover crop species and functional richness on aboveground biomass productivity, weed suppression, soil nutrient retention, soil microbial community characteristics, and performance stability. Twenty to forty cover crop treatments were replicated three to four times at eleven sites across southeastern Nebraska using a pool of eighteen species representing three cover crop species each from six pre-defined functional groups: cool-season grasses, cool-season legumes, cool-season brassicas, warm-season grasses, warm-season legumes, and warm-season broadleaves. Each species was planted …

Biology, Gene Flow, And Management Of Glyphosate-Resistant Common Waterhemp (Amaranthus Rudis Sauer) In Nebraska, Debalin Sarangi

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

Common waterhemp is the most troublesome weed in the midwestern United States. Growers from Nebraska reported failure to control common waterhemp following sequential applications of glyphosate in glyphosate-tolerant corn and soybean, which led to moderate to severe yield loss; justifying the need to confirm resistance and study the biology and management of common waterhemp. The objectives of this research were: 1) to confirm the presence of glyphosate-resistant (GR) common waterhemp biotypes in Nebraska and to evaluate their sensitivity to herbicides belonging to alternative sites-of-action; 2) to evaluate the response of common waterhemp to water stress; 3) to quantify pollen-mediated gene …

Assessing Multiple-Herbicide Resistance In A 2,4-D Resistant Waterhemp (Amaranthus Tuberculatus) Biotype From Nebraska – Student Research, Roberto Crespo

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

A waterhemp biotype was recently reported resistant to 2,4-D in Nebraska. In addition to the repeated use of 2,4-D, atrazine and imazathapyr were reported to be frequently used to control broadleaf weeds. Greenhouse experiments were conducted to confirm 2,4-D resistance and test for resistance to growth regulator herbicides and other herbicide modes-of-action (MoA). A single dose-response experiment showed reduced sensitivity in all three waterhemp biotypes to atrazine, imazethapyr and lactofen; therefore, they were generally considered resistant to those three herbicide MoA. None of the biotypes contained the Ser264 target-site mutation. Since the ametryn dose-response experiment resulted in all susceptible biotypes, …

Biology And Control Of Glyphosate-Resistant Giant Ragweed., Simranpreet Kaur

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

Giant ragweed is a troublesome, early emerging, summer annual weed found throughout the eastern and midwestern corn and soybean growing regions of the United States. Since the emergence of giant ragweed varies at different locations, our first objective was to determine the emergence pattern of giant ragweed in Nebraska and how spring tillage influences emergence. Results of a two-year study suggested that giant ragweed emerged from late March until mid-June, with the majority of emergence ceasing by early May. Spring tillage could be used as an alternative method for managing glyphosate resistant giant ragweed.

Water stress can affect the growth …

Control Of Herbicide-Resistant Volunteer Corn In Herbicide-Resistant Soybean, Parminder Chahal

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

Volunteer corn is a problem weed in soybean fields because it reduces yield and seed quality, and potentially harbors insects, pests, and diseases. Several pre-packaged herbicides have been registered in soybean in recent years, but response of volunteer corn to these herbicides has not yet been documented. Therefore, the first objective of this study was to evaluate the response of glufosinate-, glyphosate-, and imidazolinone-resistant volunteer corn to 20 pre-emergence (PRE) and 17 post-emergence (POST) soybean herbicides. The results indicated that PRE soybean herbicides partially controlled (< 80%) volunteer corn except clomazone, while acetyl CoA carboxylase (ACCase) inhibiting herbicides provided ≥ 85% control. Germination and emergence are critical stages in weed seed establishment and persistence. Scientific literature is not available about the factors affecting germination and emergence of volunteer corn. The second objective was to determine the effects of different environmental and agronomic factors on the germination and emergence of glyphosate-resistant hybrid and volunteer corn. The results indicated that response of hybrid and volunteer corn to majority of the variables tested was similar, suggesting that volunteer corn can germinate and emerge in a wide range of climatic conditions. Majority of growers control volunteer corn when it is visible above the soybean canopy, but this can results in early season competition with soybean. The third objective was to evaluate the impact of different densities of glyphosate-resistant volunteer corn at different control timings, and late season volunteer corn emergence on soybean yields. Late season volunteer corn emergence had no significant effect on soybean yield. Yield did not decrease with all volunteer corn densities, except with the highest density (10,000 plants and 500 clumps ha^-1) at all control timings. Soybean growers are looking for alternative herbicides, such …

Understanding The Biology, Inheritance And Mechanism Of Resistance Of 2,4-D Resistant Waterhemp (Amaranthus Tuberculatus) - Research Proposal, Roberto Crespo

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

Waterhemp is a very well adapted summer annual weed to the U.S. Corn Belt region. Auxinic herbicides such as 2,4-D constitute effective and widely used herbicides to control waterhemp and other broadleaf species in cereal crops and turf grasses. Recently, Bernards et al. (2012) have reported a Nebraska waterhemp biotype has evolved resistant to 2,4-D. This finding represents the sixth mode-of action herbicide group to which waterhemp has evolved resistance to. Several attributes may have contributed to make waterhemp a very successful weed and prone to evolve to herbicide resistant: a high genetic variability, aggressive growth habits and high fecundity. …