Atrazine weeds controlled

Ureides (e.g., diuron, linuron) and triazines (e.g., atrazine, simazine, ametryne) all act as inhibitors of photosynthesis and are applied to soil (see Figure 14.1 for structures). They are toxic to seedling weeds, which they can absorb from the soil. Some of them (e.g., simazine) have very low water solubility and, consequently, are persistent and relatively immobile in soil (see Chapter 4, Section 4.3, which also mentions the question of depth selection when these soil-acting herbicides are used for selective weed control). 

Atrazine, one of the herbicides most widely used in the United States and European countries over the last 30 years, is employed for pre- and post-emergence weed control on corn, wheat, barley, and sorghum fields, and on railway... 

A preemergence herbicide used for general weed control including grasses and broad-leaved weeds in a range of crops Chemical transformation product. Parent simazine and atrazine Chemical transformation product. Parent atrazine... 

The two most important compounds, atrazine and simazine, are used in two ways (B-78MI10700). At high concentrations they act as total herbicides, while at much lower concentrations they are used for selective pre-emergence weed control. The effectiveness of atrazine in maize has led to its being manufactured on the largest scale in the world... 

This book is about the revolutionary impact of the triazines herbicides, likely the most important class of agricultural chemicals ever developed. For five decades the triazines have provided weed control in more than 50 crops around the world and have helped farmers boost yields and produce enough food to feed a rising global population. The triazine herbicides, and especially atrazine, are the most well-researched herbicides in history, with thousands of scientific studies on their safety to humans and the environment. Data from studies on the triazines have been evaluated extensively by regulatory authorities around the globe to ensure their safe use. 

One of the reasons the triazines are so important in corn and other crops around the world is their application flexibility and their ability to mix with other herbicides for broad-spectrum weed control. Figure 1.6 demonstrates the relative importance of atrazine in com compared to other herbicides. 

Just as atrazine is important in com, simazine is a pre-emergence triazine that provides broad-spectrum residual weed control in many of the important fruit and nut crops when applied either alone or in combination with a contact product such as glyphosate to control weeds at the time of application (Figure 1.5). 

The benefits of the triazines in multiple cropping systems range from their application flexibility, effective weed control, soil residual activity, and crop selectivity to their important role in resistance management and conservation tillage. The triazines also have made a major impact on agricultural sustainability and crop yields, as evidenced by the use of atrazine, especially in com. 

They differ, of course, substantially as to the importance they assumed. As an example, G-27901, trietazine, was sold once in a quantity of a couple of thousand pounds for weed control in chrysanthemums in Japan and can, therefore, not be put in line with for example G-30027, atrazine. 

GS-13529, terbuthylazine A chlorotriazine similar to atrazine and simazine, terbuthylazine was first introduced to the scientific community in 1966. Terbuthylazine also provided broad-spectrum weed control in com. Studies comparing efficacy showed that generally atrazine was more effective than terbuthylazine on both broadleaf and grassy weeds. Since terbuthylazine was less efficacious than atrazine in weed control trials conducted in the United States in the late 1960s, it was not commercially developed for com in the United States. However, development for use in corn and vines continued for Europe and other countries where the weed control needs differed and the weed control differences between atrazine and terbuthylazine were not limiting. 

By the end of the 1950s, atrazine was introduced for weed control on railroad tracks and rights-of-way and in com production in Europe. The initial federal approval in the United States occurred in December 1958 when the US Department of Agriculture (USDA) registered Geigy Atrazine 50W for use in com and for nonselective weed control in noncrop areas. In 1959 Atrazine 80 W was registered, which in 1970 was trademarked as AAtrex and quickly became a leading herbicide in the United States. 

Geigy started production of simazine in 1956 in Schweizerhalle, near Basel, Switzerland 2 years later, atrazine also was produced. Use of triazines for weed control to improve crop yields grew quickly, and a production facility was installed at McIntosh, Alabama in 1959. Smaller production units were operated in Mexico, Brazil, and Australia, and important development work by Geigy led to improved production processes. In 1970 a continuous process production unit was built by Geigy Agricultural Chemicals in the United States. 

The initial federal approval of an atrazine formulation in the United States occurred December 1, 1958, when the USDA registered Geigy Atrazine 50W for preemergence and postemergence control of several broadleaf weeds on corn and for nonselective weed control in noncrop areas. A wettable powder was the most popular choice for herbicide formulations at that time and could easily be sprayed uniformly across a field. 

The next major crop use in the United States added to the Atrazine 80W label was weed control in sugarcane, approved by the USDA June 6, 1961. The 80 W formulation soon became the broadleaf weed control product of choice for sugarcane and remained so for many years until improved formulations of atrazine were developed. 

Other formulations were approved in the United States in 1965 for nonselective weed control in noncropland areas. Those formulations, which carried the Atratol brand, included a combination of atrazine, sodium chlorate, and sodium metaborate. This unique combination of ingredients, which became popular with highway departments, utilities, and railroads, provided quick bumdown of weeds and residual weed control. 

Introduction of simazine and atrazine use in corn production allowed farmers to leam novel technologies of preemergence or at-planting treatments for weed control. This required research, development, and educational programs to provide information farmers needed to modify, replace, or develop new application equipment. 

As atrazine went beyond trial use, farmers, dealers, and custom applicators hne-tuned application practices. In an effort to decrease cost and soil carryover potential, atrazine rates were decreased. Farmers moved from band to broadcast applications to achieve greater efficiency. They also sought maximum weed control by using atrazine in mixtures, especially for better grass control, tailored to each agricultural situation. 

This chapter describes the role played by atrazine, which became commercially available in the 1950s and was used extensively in com and for amenity (beautification) weed control. Corn area and yields have expanded significantly during the period since the introduction of this herbicide. Atrazine played a significant role in facilitating this expansion. 

The weed control successes of the triazines led to important discoveries about new and better ways to use herbicides. The remarkable biological success of the triazine herbicides has had a tremendous impact on weed control and crop management over a relatively short time. Sumner (1999) told of his uncle in Hastings, Kansas, who looked over his weed-free com held after he had applied his first atrazine and remarked If I didn t see it with my own eyes, I wouldn t believe it. Such accounts could be repeated many thousands of times in the late 1950s and 1960s. The triazines are still the most important herbicides for weed control in corn, sorghum, and sugarcane. 

Schirman, R. and K.P. Buchholtz (1966). Influence of atrazine on control and rhizome carbohydrate reserves of quackgrass. Weeds, 14 233-236. 

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