Atrazine broad-spectrum weed control

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. 

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. 

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. 

While many winter annual weeds controlled by atrazine and simazine may also be controlled by other herbicides, these herbicides do not provide the broad-spectrum weed control obtained with atrazine or simazine. If simazine or atrazine were not available in fine turf, the use of two or more herbicides would be required to provide equal control. Table 19.2 provides a cost comparison between triazines and alternative herbicides for weed control in warm-season turfgrasses. 

Economical weed control Atrazine provides very cost-effective weed control. The per acre cost of atrazine is competitive because the herbicide provides broad-spectrum residual control and minimizes follow-up treatments, making net return to treatment cost very good. No single alternative herbicide included in these analyses returns more value per cost invested than atrazine. 

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). 

Atrazine is the key herbicide facilitating ecofallow corn and sorghum production in the semi-arid Great Plains, where crop production is often uncertain and profits to farmers are often marginal. The success of atrazine in ecofallow is attributable to its duration of weed control as a soil-applied herbicide, the broad spectrum of weeds controlled, the low cost per area treated, and its safety to crops. In this semi-arid environment, maintaining weed-free fallow with repeated applications of nonresidual herbicides is not an economically viable alternative to atrazine. 

Atrazine remains the standard herbicide for making the transition from wheat to sorghum or corn in Great Plains cropping systems. Even where more intensified crop rotations have been developed, they are built around winter wheat followed by ecofallow sorghum or com. The success of atrazine is due to its persistence as a soil-applied herbicide, to the broad spectrum of weeds controlled, to its low cost per acre, and to its safety on sorghum and com. In the Great Plains, repeated burndown of weeds in fallow with nonresidual herbicides is not a viable alternative to the role that atrazine plays. 

With the introduction of dinitroaniline herbicides for use in fine turfgrass, the primary use for atrazine and simazine became winter annual weed control. In golf course management and sod production, a single application of simazine provides excellent broad-spectrum control of numerous winter annual species. 

Triazine herbicides are particularly well suited for conservation tillage because they provide foliar and residual control of a broad spectrum of weeds. Atrazine, simazine, and metribuzin are used in com, atrazine and propazine in sorghum, metribuzin in soybean, and simazine reduces tillage required for weed control in many perennial and tree crops. Atrazine is also used extensively in chemical fallow cropping systems in rotations involving corn, sorghum, and wheat. Cyanazine was also used extensively in corn and cotton until 2002. 

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