Use for weed control

CgH,3BrN202. A soil-acting herbicide. White crystalline solid, m.p. 158-159" C. It is a non-selective inhibitor of photosynthesis used for weed control In citrus and cane fruit plantations. It is relatively non-toxic to animal life. 

But stove oil, if not carefully used, left an oily flavor in carrots. Synthetic rubber reduced the need for guayule. Fuel oil prices had advanced to a level that almost prohibited their use for weed control. The future of oil in the herbicide field was in doubt. Yet farmers needed oil sprays for their irrigation systems, which were infesting their fields with weeds, and for their fence lines, which were harboring thrips and other insects and diseases. These problems of research were undertaken by the agricultural experiment stations in California, Massachusetts, New York, and other states. 

It is important that herbicides used for weed control in crops are selective to that crop. Early compounds used the inability of the foliage of upright cereal crops to retain a great deal of spray as the basis of their selectivity and this was successful in many situations although it must be remembered that the alternative to weed control with inadequately selective herbicides was hand weeding or no weed control at all. 

Runham, S.R., Town, S.J. and Eitzpatrick, J.C. 2000. Evaluation over four seasons of a paper mulch used for weed control in vegetables. Acta Horticulturae 513 193-201. 

Arsenic trioxide finds major use in the preparation of other compounds, notably those used in agricultural applications, The compounds monosodium methylarsonate. disodium methylarsonate, methane arsenic acid (cacodylic acid) are used for weed control, while arsenic acid, H3ASO4, is used as a desiccant for the defoliation of cotton crops, Other compounds once widely used in agriculture are calcium arsenate for control of boll weevils, lead arsenate as a pesticide for fruit crops, and sodium arsenite as a herbicide and for cattle and sheep dip. In some areas, arsenilic acid has been used as a feed additive for swine and poultry. Restrictions on these compounds vary from one country and region to the next. 

Exercise 14-23 Both 2,4-D and 2,4,5-T are herbicides that have been used for weed control and as defoliating agents in jungle warfare. Apart from the arguments for or against the use of chemicals for such purposes, there have been reports of serious dermatitis among the industrial workers who produce these substances. 

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. 

Norwood and Currie (1996) showed that yields and profitability of ecofallow corn at Garden City, Kansas, were superior to yields and profitability where V-blade tillage was used for weed control in the fallow period. They concluded that no-till is essential for adequate yields in dry years and usually will result in yield increases even in years with more favorable climatic conditions. This study was conducted in a region of the central Great Plains where there has been little dryland corn production since early in the 20th century. At present, no other herbicide approaches the economic and biological advantages of atrazine. 

Ametryn, another triazine herbicide, was previously used for weed control in citrus. This herbicide first appeared in recommendations in 1979 for control of broadleaf weeds, annual grasses, and some perennial grasses. Ametryn was recommended at use rates of 3.6-7.2kg a.i./ha, with a maximum of 5.4kg a.i./ha for both shallow, poorly drained flatwood soils (soils having more organic matter and clay) and bedded groves (trees planted on raised beds). It was recommended that ametryn should not be applied to trees less than 2 years old. Between 1984 and 1988 the application rates were increased to 7.2-10.8kg a.i./ha, with the annual rate not to exceed 13.6kg a.i./ha, and with lower rates... 

Kraus, as editor of the plant physiology journal Botanical Gazette, quickly published the full results side by side in December 1944. Both papers cite correspondence with Kraus in 1941 for the idea that hormones could be used for weed control. [24] By this point Kraus evidently recognized the agricultural potential of 2,4-D and 2,4,5-T as herbicides, and may have been seeking to establish a priority date for conceiving this invention (a move with major intellectual property implica-... 

Mixtures with other herbicides also are used for weed control. The product Agent Orange, used extensively throughout Vietnam, was about 50% 2,4-D. However, the controversy about the use of Agent Orange was associated with a contaminant (dioxin) in 2,4,5-trichlorophenoxy acetic acid (2,4,5-T) (C8H5Cl303), not with 2,4-D. It should be well understood that 2,4,5-T is different from 2,4-D but similar to 2,4-D as a herbicide component of the defoliant.39... 

Numerous herbicides are currently recommended and used for weed control in agricultural, industrial, and recreational areas. However, the method of formulation and application of such chemicals to plants or soils may markedly affect their biological efficacy and persistence. Chemical additives (primarily surfactants) in both oil and aqueous sprays are already used widely, and when properly understood, promise a virtual revolution in the use of agricultural chemicals. Conceivably, not only weed control performance and herbicidal selectivity can be altered but also distribution, metabolism, and accumulation of chemical residues. With the widespread introduction and increasing use of chemical additives in weed science and technology, we must therefore learn to reflect on what before we knew about the use of herbicides. 

T ichlobenil (2,6-dichlorobenzonitrile) is used for weed control in cranberry marshes, in nursery stock and woody plants, for pre-emergent control in crops, and for aquatic weed control. The acute toxicity of dichlobenil to fish has been measured at the Fish-Pesticide Research Laboratory in Denver the 24-hour-LC50 values are 22 p.p.m. active ingredient to bluegills (Lepomis macrochirus Rafinesque) at 24 °C. and 23 p.p.m. to rainbow trout (Salmo gairdneri Richardson) at 13°C. 

Plants have active and passive mechanisms for resistance to most microorganisms. Since chemicals used for weed control interfere with metabolic processes of plants, interactions between herbicides and plant pathogens are to be expected. Interactions commonly, although not always, result in increased disease associated with herbicide use. Several examples of disease enhancement by herbicides were described in the preceding chapter. We describe here a less common phenomenon where certain fungi that colonize plant roots enhance the efficacy of a herbicide. 

Absdsic add, effea on growth of etiolated wheat coleoptiles, 8334T Absdsin II, Set Absdsic add Aetna chondriUat Canestrini, use for weed control, 136... 

Flooding—Flooding has long been used for weed control in rice, water covers the entire weed, killing it by suffocation. 

Ammonium salts were also used for weed control. These salts, ammonium thiocyanate, ammonium nitrate, ammonium sulfate, along with ammonium sulfamate were used as foliar sprays. The modes of action of these ammonium salts along with the use of other salts such as iron sulfate and copper sulfate cause desiccation and plasmolysis. 

Diphenyl-ether herbicides such as aclonifen, bifenox and lactofen are relatively new herbicides, used for weed control in the growth of seeded legumes, such as soybeans. MS and MS-MS of five neutral diphenyl-ethers herbicides and three acid metabolites was reported [64]. Negative-ion ESI is preferred for the acidic compounds [47, 64] and either negative-ion APCI [64] or positive-ion ESI [47] is used for the neutral ones. Stmcture informative fragmentation was observed in negative-ion MS-MS [64]. 

In the 1950s and 1960s, Geigy and other firms developed a series of herbicides based on alkyl and dialkyl triazines, such as the root-herbicide atrazine (83)64. They are made by stepwise introduction of suitable nucleophiles into precursors. Other members are ametryn, the non-selective simazine (84) and the cyanuric chloride-derived methylthio triazine desmetryne (85) (Scheme 19). Chlorotoluron is 3-(3-chloro-p-toly 1 )-1,1-dimethylurea (86), a phenylurea herbicide. These products act on the photosynthetic pathway. Both 83 and 84 are used for weed control in maize65. Sulfonylureas such as the triazine chlorosulfone (87) inhibit the enzyme acetolactate synthase. They offer the major advantage of requiring no more than 10 to 20 g per hectare. 

Phenylurea herbicides are widely used for weed control around the world. This method works directly on a filtered river water sample. This fully automated method was accomplished on the PROSPEKT automated system and was interfaced directly to an HPLC. Figure 10.18 shows the configuration of the system. It consists of the solvent delivery unit (SDU), which prepares the sorbent, pumps the sample, and elutes the cartridge. The system also includes Marathon autosampler, which coordinates the 10-mL water samples, and the... 

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