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Adjuvants are used in agriculture to improve herbicide activity or application performance. The addition of adjuvants to herbicide solution can enhance its penetration, wettability, and evaporation rates by altering density, viscosity, contact angle between the droplet and plant surface, and droplet surface tension. Furthermore, those alterations in the physical properties of the herbicide solution can result in changes in the droplet-size distribution that directly impact herbicide efficacy. The adoption of glufosinate-based herbicide programs has increased with the widespread occurrence of glyphosate-resistance (GR) weeds in recent years. Also, tank mixture of dicamba and glyphosate has been largely adopted for broad-spectrum weed control since the release of dicamba/glyphosate-tolerant soybeans in 2017. Therefore, it is essential to understand the influence of adjuvants on the performance of those commonly used herbicides. The objectives of this research were: (1) determine the physical properties (density, viscosity, dynamic surface tension, static contact angle, and droplet evaporation rate), and droplet size distribution of glufosinate, and dicamba plus glyphosate solutions in tank-mixture with adjuvants and (2) evaluate the response of weed species to glufosinate, and dicamba plus glyphosate solutions in tank-mixture with adjuvants under greenhouse and field conditions.
Adjuvants are known to enhance spray droplet retention on leaf surfaces and penetration of herbicide active ingredients through cuticles due to changes in physical properties such as density, viscosity, surface tension (SFT), and contact angle (CA) increasing leaf wettability. However, previous research has shown that the performance of an adjuvant is dependent on the herbicide with which it is applied, the plant species, and environmental conditions. The objectives of this study were to determine the effect of adjuvants on these physical properties when glyphosate and lactofen are applied alone and in combination and to determine if these changes can be correlated to herbicide efficacy. The impact of the addition of the adjuvants into the treatment solutions was greater on viscosity than on density values. Overall, adjuvants significantly decreased the SFT of treatment solutions when compared to either water or herbicides alone. In addition, reduced CA was observed due to the reduction in surface tension. However, results were adjuvant- and species-dependent. Herbicide efficacy was only partially explained by the changes in these physical properties. Observations from this study highlighted the importance of adjuvants on reducing SFT and CA properties of spray solutions; however, further investigation is needed to better understand the factors influencing herbicide uptake and how they are correlated in order to maximize herbicide efficacy.
Over the past several years, numerous anecdotes from aerial applicators have surfaced concerning observations of increased numbers of fine droplets seen in the applied spray clouds, often associated with tank mixtures that contain crop-oil concentrates (COCs) and foliar fertilizers (FFs). Efforts were made herein to correlate surface tension and viscosity to spray droplet size under a variety of aerial application conditions, but these efforts were unsuccessful. In addition, spray mixtures were examined to compare relative evaporation rates. Researchers are encouraged to actively pursue this line of work. The addition of several adjuvants and FFs were found to significantly affect spray droplet size, so applicators should pay careful attention to spray tank composition when making aerial spray applications.
The effect of Sta-Put® and Silwet® L-7607 on physical properties (viscosity, surface tension and volatility), droplet spreading and drying rates, and foliar uptake and translocation of glyphosate was studied using white birch seedlings and branch tips. Three end-use mixtures were prepared using Vision®, one in water alone and the other two with 0.05% of the adjuvants in water. Physical properties were measured to examine their roles on droplet spreading and drying rates. Foliar uptake was investigated to study the effect of droplet spreading and drying rates on foliar retention; and translocation was studied to examine the role of the two polymers on bioavailability of glyphosate.
This study was designed to determine if the present USDA-ARS spray-nozzle models, which were based on spray solutions of water plus non-ionic surfactant, could be used to estimate spray droplet-size data for different spray formulations through use of experimentally determined correction factors. Twelve spray-solution treatments were evaluated, ten of which contained a formulated glyphosate product and nine of these contained an additional tank-mix adjuvant. Droplet-size testing was conducted across multiple operational points (nozzle-orifice size, nozzle orientation, spray pressure, and airspeed), in a high-speed wind tunnel, which corresponds to the response surface experimental model used to develop the present spray-nozzle models. The hypothesis that the different treatment solutions would respond linearly across a range of operational parameters and that a correction factor from relative to water plus non-ionic surfactant solution was proven false. When compared to water or the water plus non-ionic surfactant, the changes in atomization across the operation spectrum of the nozzle were not consistent and varied by formulation. Attempts to apply regression fits for a correction factor based on solution physical properties were not successful. With the formulated glyphosate tank mix used, none of the adjuvants tested, except the polymer, showed significant changes in droplet size under the high air shear regime. Whereas there is likely a need to develop formulated product-specific atomization models, the further addition of adjuvants do not significantly change the atomization characteristics, and, as such, should not require a unique spray-nozzle model.
An introduction to herbicide action; Reaching the target; Oxigen toxicity and herbicidal action; Microtubule disruptors; Herbicide effects on lipid synthesis; Nucleic acid and protein synthesis inhibitors; Inhibition of amino acid biosysnthesis; Herbicides with auxin activity; Other sites of herbicide action; Secondary physiological effects of herbicides; Herbicide interactions with herbicides, synergists, and safeners; Naturally occurring chemicals as herbicides.
Herbicides are one of the most widely used groups of pesticides worldwide for controlling weedy species in agricultural and non-crop settings. Due to the extensive use of herbicides and their value in weed management, herbicide research remains crucial for ensuring continued effective use of herbicides while minimizing detrimental effects to ecosystems. Presently, a wide range of research continues to focus on the physiology of herbicide action, the environmental impact of herbicides, and safety. The authors of Herbicides, Physiology of Action, and Safety cover multiple topics concerning current valuable herbicide research.
The late 1980s saw an explosion in the amount and diversity of herbicide resistance, posing a threat to crop production in many countries. The rapid escalation in herbicide resistance worldwide and in the understanding of resistance at the population, biochemical, and molecular level is the focus of this timely book. Leading researchers from North America, Australia, and Western Europe present lucid reviews that consider the population dynamics and genetics, biochemistry, and agro-ecology of resistance. Resistance to various herbicides is discussed in detail, as well as the mechanisms responsible for cross resistance and multiple resistance. This reference is invaluable to those interested in evolution and the ability of species to overcome severe environmental stress.
This completely updated and revised Second Edition of the popular Workbook of Atmospheric Dispersion Estimates provides an important foundation for understanding dispersion modeling as it is being practiced today. The book and accompanying diskette will help you determine the impacts of various sources of air pollution, including the effects of wind and turbulence, plume rise, and Gaussian dispersion and its limitations. Information is shown in summary graphs as well as in equations. The programs included on the diskette allow you to "get the feel" for the results you'll obtain through the input of various combinations of parameter values. The sensitivity of data to various parameters can be easily explored by changing one value and seeing the effect on the results. The book presents 37 example problems with solutions to show the estimation of atmospheric pollutant concentrations for many situations.