Total weed control

Diuron is used for the control of annual weeds in front crops and total weed control in non-crop situations. 

So far, it has been established that there is a very large market for crop protection agents globally and that these markets are dominated with crops such as wheat, barley, maize, soybeans, rice, cotton, grapes, top fruit and total weed control in countries and regions such as the USA,... 

Dalapon, like TCA, is a contact selective herbicide for the control of grassy weeds. It is used for selective weed killing at a rate of 0.8-10 kg acid equivalent/ha, and for total weed control on non-crop areas at a rate of 10-25 kg/ha. 

Chlorthiamid is a preemergence herbicide inhibiting germination, used at a rate of 20-30 kg active ingredient/ha for total weed control, at 4-14 kg active ingredient/ha for selective weed control. It is recommended as spot treatment to control docks (Rumex spp.) and thistles (Cirsium spp.) in the renovation of old pastures. Its other areas of application are the same as those of dichlobenil (Sandford, 1964 Jenner, 1977). 

It can be used for selective and total weed control at a rate of 1-7 kg active ingredient/ha. Sugar beet is particularly tolerant to asulam. 

Applied at rates of 10-30 kg active ingredient/ha they provide total weed control on nonncrop areas. At these rates, they remain active for 2 years in the soil, so that no crops should be sown in the treated areas. 

Applied at rates of 0.S8 kg active ingredient/ha it kills all annual grass and broadleaved weeds. At low rates it is used for selective weed control on sugar cane, pineapple and pastures, while at higher rates it provides total weed control on noncrop areas, highways and industrial areas. High doses also kill woody weeds. Cyperus spp. are resistant to tebuthiuron. 

Sulfadiazole is an experimental herbicide for pre- and postemergence application. Used at a rate of 1.5-7 kg active ingredient/ha it is effective against most of the annual and perennial weeds. It is a herbicide for total weed control. When applied postemergence, combination with a contact herbicide is recommended to improve the burn-down effect. Its residual effect is longer than 6 months. The acute oral LDjo for rats is 5000 mg/kg. 

Paraquat is used for stubble cleaning, presowing and preemergence weed control, inter-row weed control of ploughed land, as a spray for subfoliar weed-control in maize, for inter-row weed-control in orchards, vineyards and tree nurseries, for pasture renovation and for total weed-control in non-crop areas. The rate of application is 0.4-1.5 kg active ingredient/ha. 

Buthidazole effectively controls most annual grasses and broad-leaved weeds. It is recommended at rates of 4-13 kg active ingredient/ha for total weed control in non-crop areas. Applied at a lower rate it can be used as a selective herbicide in maize, sugar cane and pineapple plantations. Depending on rainfall, the activity of buthidazole persists for 12-15 months. 

Inorganic arsenic compounds were discussed in the chapter on inorganic herbicides. The use of organic arsenic compounds began in the 1950s in the USA. Even today several substituted arsenic acid derivatives are used only in the USA for total weed-control on non-crop land, on cotton and for turf treatment. Methylarsonic acid (MMA, I) is a strong dibasic acid, readily soluble in water and in ethanol. 

To increase its effect against broad-leaved weeds it is used in combination with herbicides efficient For the control of such weeds. Used in tank mixture with phenmedipham, it hives total weed-control in sugar beet (Hubl et ai, 1977). 

Ustilan . [Bayer] Ethidimuion herbicide fcx total weed control on nonciop land. 

Toxicology LD50 (oral, rat) > 5000 mg/kg, (oral, mouse) > 2500 mg/kg Uses Herbicide for total weed control on noncropland... 

Between 1979 and 1991, the amounts of herbicide apphed in the United States have remained constant, but the expenditures on herbicides have increased 54%. Agricultural costs accounted for ah. of this increase and more, since herbicide user expenditures in the government/commercial and home sectors combined dropped 3 to 4% during that period. Increased weed control costs related to crop protection have also contributed to the 37% increase, since 1988, in total annual user expenditures for pesticides in general, ie, herbicides, fungicides, and insecticides. In the United States, agricultural uses (ca 1993) account for more than 67% of total pesticide user expenses and 75% of the quantity used annually. Herbicides are now the lea ding type of pesticides in terms of both user expenditures and volumes used (1). 

The immediate and total removal of weeds is often recommended. However, this recommendation may be based more on when control methods can most easily be appHed, rather than on considerations of the optimal time for effective weed control (454). Controlling plants that are not actually problems or that are present at noncritical times is cosdy and may not truly benefit the producer. However, weeds that are present initially ia very low numbers may require subsequent eradication if iatroduction of a new noxious species is to be prevented. 

Plants can also be pests that need to be controlled, particulady noxious weeds infesting food crops. Prior to 1900, inorganic compounds such as sulfuric acid, copper nitrate, sodium nitrate, ammonium sulfate, and potassium salts were used to selectively control mustards and other broadleaved weeds in cereal grains. By the early 1900s, Kainite and calcium cyanamid were also used in monocotyledenous crops, as well as iron sulfate, copper sulfate, and sodium arsenate. Prom 1915 to 1925, acid arsenical sprays, carbon bisulfate, sodium chlorate, and others were introduced for weed control use. Total or nonselective herbicides kill all vegetation, whereas selective compounds control weeds without adversely affecting the growth of the crop (see Herbicides). 

The estimated cost of equipment, labor, and herbicides for weed control within a specific crop can be very expensive. For example, in 1980, cotton was planted on 5.2 million ha in the United States. The total cost for equipment, labor, and herbicides used to control weeds was estimated to be 547 million (20). Herbicides account for 32% of the total cost while equipment and labor costs were 34% each. 

The total cost for full-season weed control varies considerably with a specific crop or among different crops (21, 22). The production environment, especially the amount of available moisture influences the weed control strategy and the costs incurred. For example, in cotton the total cost for full-season weed control in West Texas was 76/ha, but in the Mississippi Delta the cost was 156/ha (20). 

Weeds constitute one of the major problems in agriculture. They are an important constraint on yield in most crops across the world. These days, growers spend much money on weed control. About 6 million ton of herbicides was sold in the world in 2006 and herbicides are the most used pesticides they form approximately 38% of the total amount of pesticides (FAO 2006). Nowadays, an effort to tighten rules for authorization and application of pesticides, research and develop products that are target-specific, degrade quickly and do not accumulate in the food chain, exists in... 

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... 

Performance and market share for competitive herbicide products Since the USEPA Special Review was initiated in 1994, acres treated with various corn herbicides have been carefully monitored. No clear alternative has proved to be a possible replacement to atrazine. Several facts are noteworthy. No corn herbicide introduced between 1994 and 2000 reached a 10% market share, nor did the market share increase for putative atrazine replacements like 2,4-D or bromoxynil (Table 13.6). These new products suffered from one or more of the following limitations limited spectrum of weeds controlled, crop injury potential, or rotational restrictions. Meanwhile, atrazine s total market share remained constant at approximately 70%. To date market retention has been poor when new herbicides are used alone. Virtually all com herbicides introduced since 1994 are used with atrazine, and the percentage of acreage treated in combination with atrazine is increasing (Table 13.6). 

Unlike the transformation processes that reduce the total amount of triazine present in soil, retention only decreases the amount available for weed control, microbial transformations, or transport. The amount retained or sorbed by soil can range from 0% to 100% of the amount applied, but sorption on silt loam, loam, or clay loam soils typically ranges from 50% to 80%. Triazine retention in soil is influenced primarily by organic carbon content, soil clay content and type, and soil pH. Other factors influencing retention include the amount of triazine applied, the amount of dissolved organic carbon (DOC) in soil solution, soil water content, and triazine to soil contact time (aging). 

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