Weed control sugarcane

Since these products are in the introductory phase in the sugarcane market, their impact on sugarcane weed control practices is still being defined. 

Rapid growth of chemical weed control did not occur until after World War II when a herbicide was introduced by Jones in 1945 at the Imperial Chemical Industries of England 2,4-dichlorophenoxyacetic acid (2,4-D). Its utility has come from its ability to kill selectively broadleaf weeds in cereal grains, com, and cotton. It does not disturb the soil and is not persistent. 2,4,5-T was launched commercially by American Chemical Paint Co. in 1948 (now Union Carbide) to combat brush and weeds in forests, along highways and railroad tracks, in pastures, and on rice, wheat, and sugarcane. 

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. 

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. 

Frear and Swanson (1970) isolated a soluble glutathione S-transferase from com leaves. Active enzyme preparations were also isolated from leaves of sorghum, sugarcane, johnsongrass, and sudangrass. Appreciable enzyme activity was found only with substituted 2-chloro-.v-triazincs. Substitution of a methoxy, methylmercapto, or hydroxy group in the 2-position of the triazine ring resulted in loss of weed control. 

Triazine herbicides provide selective weed control in crops such as corn, sorghum, and sugarcane. In addition, some members of the triazine family are used for weed control in orchards, horticultural, and perennial crops, etc. A unique selective use of triazine herbicides is in triazine-tolerant rapeseed. Although triazine herbicides provide control of a wide variety of grass and broadleaf weeds, the long-term, widespread, and repetitive use of triazine herbicides in crop and noncrop situations has led to the selection of many triazine-resistant weeds. The physiological and biochemical basis of triazine selectivity between crops and weeds and of resistance to triazine herbicides in weeds is well understood. 

Weed Control in Sugarcane and the Role of Triazine Herbicides... 

Furthermore, the triazine herbicides have freed operators from much of the laborious burden of weed control, enabling them to manage other resources to maximize returns of both agricultural and milling operations. Since atrazine and ametryn were introduced, the genetic potentials of sugarcane cultivars have been more fully realized because the soil tillage and water losses have been reduced. 

Case studies from Hawaii and Louisiana document a dramatic decline in the development of sugarcane herbicides. Evidence shows that the decline in the Hawaiian sugarcane acreage was attributable, at least in part, to delays in commercializing new weed control products (Smith, 1998b). 

Plows and animal-powered cultivators were not commonly used on most sugarcane properties until after labor shortages occurred. As the massive hand-hoe crews all but disappeared from sugarcane fields, animal-drawn implements provided weed control. By 1928, one animal-powered riding cultivator did the work of 20 men with hoes (Earle, 1928). 

After World War II, mechanization became virtually essential for weed control and resulted in dramatic adoption of tractors in sugarcane. In Louisiana, the number of tractors on sugarcane farms doubled between 1940 and 1947. During this same period, sugarcane acreage in Louisiana increased 20% while farm labor decreased 40%. Much of this change was due to cultivation with tractors and the introduction of 2,4-D for broadleaf weed control (Conrad and Lucas, 1995). 

Flame cultivation was attempted in sugarcane in the 1940s (Conrad and Lucas, 1995), but was soon abandoned. Liquid propane flamers burned broadleaf and grassy weeds as shields partially protected the crop from thermal damage. While flame cultivation was only marginally useful in sugarcane, tractor-mounted weed burners have been important in the transition from dependence on repetitive mechanical cultivation to the concept of chemical energy for weed control. 

Chemical weed control in sugarcane may have started in Hawaii. Sodium arsenite was first used in rubber plantations in 1913, but its most lasting impacts occurred in the sugar industry. At that time the Hawaiian industry was spending 750000 to 1 million annually for hand hoeing, but growers learned that they could apply sodium arsenite at 5.5kg/ha in 380L of water and achieve weed control at one-fourth the cost. 

In 2003-2005,42% of US sugarcane was treated with 2,4-D, the second leading herbicide in the crop. This chemical is inexpensive, controls a wide range of annual and perennial broadleaf weeds, and complements the spectrum of weeds controlled with triazine herbicides. However, 2,4-D is restricted in many areas to protect nearby sensitive crops, such as cotton and vegetables. If 2,4-D were not available for use in sugarcane, the net economic loss to the US sugarcane industry is estimated to be 51 million annually (Nalewaja, 1996). 

Historically, tillage and hand weeding were the main methods of weed control. Since the advent of herbicide use in 1950, essentially all sugarcane in Australia now receives one or more herbicide applications. Virtually all of the crop is produced on family-operated, commercial-scale farms and is processed at cooperative or privately owned mills. 

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