Simazine 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). 

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... 

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). 

Research had confirmed that no parent simazine residues were found in treated com plants, and additional data on the dissipation pathway of simazine needed to be developed. Research also indicated that triazines interfered with the photosynthetic process on susceptible growing weeds, as evidenced by the appearance of chlorotic leaves. Steps were undertaken to elucidate simazine s dissipation pathway and herbicidal mode of action. In Basel, Dr. Gast (1958) showed that the accumulation of starch by common coleus (Coleus blumei Benth.) plants was inhibited from treatment with 2-chloro-4,6-bis-(alkyl-amino)-triazines due to the inhibition of sugar synthesis. At the same time, Moreland et al. (1958) found weed control activity could be reduced by supplying carbohydrates to the plants through their leaves and that simazine was a strong inhibitor of the Hill reaction in photosynthesis. Exer (1958) found that triazines inhibited the Hill reaction as strongly as urea of the CMU (monuron) type. 

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. 

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. 

Simazine also became widely used in industrial weed control. It was effective, stable, and did not leach as readily as alternatives. Highway departments sprayed simazine under guardrails to eliminate the need for mowing. Railroads and utilities used simazine in mixes with other herbicides to get longer-lasting control of shallow germinating weeds. 

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. 

During the late 1950s and early 1960s, most soil-applied herbicides typically did not receive mechanical incorporation, and when rain was insufficient, lacked reliability in controlling weeds. The reason for the slow adoption of mechanical incorporation techniques was probably three-fold (a) banded applications were preferred from a cost standpoint (b) the advantages of soil incorporation were not universally recognized and (c) the equipment and techniques for adequate incorporation were not available. Poor soil incorporation not only resulted in poor weed control, but in some cases resulted in crop injury. Simazine, in spite of its good weed control spectrum in corn, was never widely used in the Central Plains. Its lack of acceptance was attributed to its soil residual with the potential to injure... 

The triazines played a significant role in the transformation of agriculture in the latter half of the 20th century - in Europe and around the world. Terbutryn was extensively used at one time for grass weed control in winter cereals. Terbuthylazine has played a major role in com and in weed control of peas and other broadleaved legume crops. Simazine has been used on a large scale for weed control in crops. 

Novartis Crop Protection, Inc. (1997). Supplement to Novartis benefit analysis of atrazine and simazine Additional information on weed control, yield and impact to growers and livestock producers. Submitted to USEPA. Public Docket OPP-30000-60. 

Broad-spectrum weed control Atrazine and simazine control a broad spectrum of broadleaf and grass weeds. In fact, of the 28 weeds species considered in the analysis, atrazine provides a higher level of control of a greater number of them than any other herbicide. 

Simazine was among the first herbicides registered for use in Florida citrus in 1962 and was recommended by the University of Florida as an excellent weed control tool for citrus (Kretchman and McCown, 1962). This early registration of simazine was for the control of annual weeds, while today s registration includes broadleaf weeds, annual vines, and annual grasses (Singh and Tucker, 1987). 

Pickett et al. (1992) reported that California citrus growers depend on herbicides for weed control. Simazine was rated as the most important herbicide used in citrus production. Abdel-Rehman et al (1994) reported that control of annual broadleaf weeds was most effective with simazine plus fluazifop and least effective with fhiazifop alone. Application of diuron or atrazine once at 1-4kg a.i./ha or twice at 1 + 1, 1 + 2 or 2 + 2kg a.i./ha, significantly reduced grasses and broadleaf weeds. Broadleaf weeds were controlled by 2-4kg a.i./ha of diuron and 2 + 2kg a.i./ ha of simazine at the 60-day sampling period (Singh et al, 1987). Perez (1976) reported that fluometuron, diuron, monuron, and simazine, all at 4.8kg a.i./ha, and bromacil at 4kg a.i./ha controlled weeds without injury to citrus on latosols, while simazine and diuron at 4.8 kg a.i./ha or bromacil at 4kg a.i./ha caused no injury to grapefruit after two applications on sandy soil. 

Triazine herbicides, principally simazine, have been an integral part of this change in management practice. Simazine is used alone and in combination with other preemergence herbicides for weed control in the plant row. It has low water solubility, low volatility, long residual activity, and gives a broad spectrum of annual weed control. 

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