Atrazine sorghum crops

Comparative analyses and computer simulations revealed no true replacement(s) for triazine herbicides. Nonchemical alternatives were limited to cultivation and cultural practices, neither of which is very effective when used alone. The environmental costs of cultivation are simply too great, and repeated cultivation of the nation s com and sorghum crops is not feasible. Several chemical alternatives were considered, each revealing its own particular weakness (Bridges, 1998). Relative to atrazine use in com and sorghum, the following characteristics were identified as nearly irreplaceable benefits. 

Swain, DJ. (1981). Atrazine dissipation in irrigated sorghum cropping in southern New South Wales. Weed Res., 21 13-21. 

Atrazine is used in agriculture to control growth of annual grass and hroadleaf weeds and is the most widely used herbicide in corn and sorghum crops. Atrazine specifically inhibits photosynthesis in plants by preventing electron... 

Atrazine, a triazlne compound, is extensively used as a selective herbicide on corn and sorghum fields for the control of broadleaf and grassy weeds. Depending on soil properties and climatic effects, its persistence from recommended application rates in north central states may extend well beyond one year and crop injury may result when sensitive species are in the rotation (50). 

Terbutryn soon found markets in various crops and occupied important niches. Mixtures of low rates of terbutryn with near normal rates of atrazine have been used. Further opportunities for terbutryn were found in pea, broad bean (Viciafaba L. var major (Harz.)), common vetch, potato (always in mixture with simazine, or later with terbuthylazine), and sunflower, as well as grain sorghum and sugarcane in special situations. Terbutryn was the last candidate to reach the market during the first 15 years of the herbicide project. 

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. 

The metabolism of atrazine and a series of 2-chloro-.v-lriaz.ines were reported by Lamoureux et al. (1972) in excised leaf or shoot tissue of barley, corn, sorghum, and sugarcane. The authors found that the primary route of metabolism was the displacement of the 2-chloro group with glutathione or 7-glutamylcysteine. The overall rate of metabolism in susceptible barley was much slower than in tolerant crops. 

Within North America and a few other countries, most triazine-resistant weed biotypes have been reported after repeated use of atrazine in com and sorghum. In some areas of Western Europe and other countries, triazine-resistant weeds have been reported after repeated use of simazine in orchards and along roadsides. A few triazine-resistant weeds (e.g., kochia, cheatgrass, and common groundsel) have biotypes with triazine resistance in nurseries and perennial tree crops, as well as along railways and roadsides. 

The 10 separate studies are listed in Table 12.1. The authors, time of completion, crops included, and aggregate economic costs based on atrazine or triazine availability are shown when they were available. Because most of the atrazine used is on corn and sorghum, these studies focus on these crops. 

This comprehensive biological and economic study for the field com and sorghum sectors included large amounts of data to give separate cost estimates if atrazines or triazines were not available. University weed scientists efficacy ratings on all major herbicides on all weed species, unit costs of all herbicides and cultivation treatments, acres or hectares planted, weed densities, and current herbicide use patterns were compiled for each of the 10 USDA production regions as described by Ciba Crop Protection (1995) and Bridges (1998). Almost 5000 university and Ciba Crop Protection field trials were compiled in these analyses. 

There are yield and weed control costs in other commodities besides corn and sorghum. Sweet corn and popcorn have similar weed pests, but fewer herbicide substitutes than field corn. Of course, these crops are more valuable crops per area than field corn, so losses per acre are large relative to field corn. Both yield and cost of production changes were computed for sweet com and popcorn using the same agronomic and analytical approach as for field com. Sweet com losses are estimated to be 80.5 million and 62.4 million if triazines or atrazines were not available, respectively. 

The sum of com and sorghum sector costs, off-farm costs and costs to minor crops is 1.66 billion without triazines and 1.47 billion without atrazine. This includes the savings to taxpayers from lower farm program payments, based... 

Soon after its initial registration, atrazine became a widely used herbicide in the United States (Padgett et al., 2000). In 1994 at the time the USEPA Special Review was initiated, atrazine was used on approximately 67%, 65%, and 90% of US corn, sorghum, and sugarcane acreage, respectively. These 1994 percentages of crop treated remain consistent today. 

Analysis approach - corn and sorghum A two-tiered approach was also used to characterize the benefits associated with uses of atrazine and simazine in corn and sorghum. First, a comparative analysis was made of product labels. The following parameters were considered in this review performance profiles, including efficacy, spectrum, and crop tolerance label comparisons physical and chemical characteristics of the product hazard profiles economic benefits and other relevant issues, such as use restrictions, etc. 

Table 13.5 A computer simulation of projected US regional changes to grain sorghum growers if atrazine had not been available for use during the 1995 crop year3...

As new herbicides were introduced over the years, weed scientists and farmers looked for the best mixtures, rates, and ratios to determine where the new ones would fit. The objective was always to provide the grower with the most dependable and efficacious control of major weeds, with the least amount of herbicides and cost, and with little or no risk to the applicator, consumers, and environment. With corn, sorghum, sugarcane, and certain other crops, such mixtures most often included atrazine or other triazine herbicides. Many times as weed scientists or farmers would discuss the virtues and performance of new herbicides, they would state The new products performed well, but it sure helped to add a little atrazine. ... 

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. 

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