Weed-killers, Herbicides

SYNS BOREA BROMAZIL 5-BROMO-3-sec-BUTYU6-METHYLURACIL 5-BROMO-6-METHYL-3-(l-METHYLPROPYL)-2,4(lH,3H)-PYRIMIDINEDIONE 5-BROMO-6-METHYL-3-(l-METHYLPROPYL)URACIL 3-sek.BUTYL-5-BROM-6-METHYLURACIL (GERMAN) CYNOGAN DU PONT HERBICIDE 976 EEREX GRANULAR WEED KILLER EEREX WATER SOLUBLE CONCENTRATE WEED KILLER HERBICIDE 976 HYVAR HYVAREX HYVARX ... 

Weed-killers (herbicides) are the chemical tools for controlling weeds harmful to crops. They include a great variety of types both in the chemical sense and with respect to their mode of action. According to their mode of application, we may distinguish foliar herbicides and soil herbicides, and according to the time of application, pre- and postemergent herbicides. 

In North America, calcium cyanamide is no longer used as fertiliser, but it has limited use in special agricultural appHcations for defoHants, fungicides, herbicides, and as a weed killer. The primary industrial use is as a chemical intermediate for the manufacture of calcium cyanide, hydrogen cyanamide solution, and dicyandiamide. Calcium cyanamide is also used to add nitrogen to steel. 

Paraquat is a broad-spectrum contact weed killer and herbage desiccant that is used widely in agriculture and horticulture. Paraquat was originally formulated in 1882, but its herbicidal properties were not discovered until 1955. Since its introduction in the early 1960s, paraquat has been used extensively in about 130 countries, including the United Kingdom, Canada, and the United States, on a wide variety of agricultural crops (Fletcher 1974 Haley 1979 Kelly et al. 1979 Anonymous 1988). 

In the past 10 years, chemical weed killers have replaced the machete and the hoe to a large extent in the tropics, especially in sugar cane fields. More than any other chemical, 2,4-D and its derivatives are used. Herbicides could also be used profitably to a greater extent in crops such as pineapple, rubber, rice, coffee, pastures, and lawns. Methods and chemicals used in Puerto Rico are described and results are compared with other areas. 

Uses Systemic herbicide weed killer and defoliant. 

Synonyms AF 101 AI3-614378 Anduron Ansaron Bioron BRN 2215168 Caswell No. 410 CCRIS 1012 Cekiuron Crisuron Dailon DCMU DCMU 99 Dialer Dichlorfenidim 3-(3,4-Di-chlorophenol)-l,l-dimethylurea 3-(3,4-Dichlorophenyl)-l,l-dimethylurea A -(3,4-Dichloro-phenyl)-A,A-dimethylurea l,l-Dimethyl-3-(3,4-dichlorophenyl)urea Dion Direx 4L Diurex Diurol DMU DP hardener 95 Duran Durashield Dynex EINECS 206-354-4 EPA pesticide chemical code 035505 Farmco diuron Herbatox HW 920 Karmex Karmex diuron herbicide Karmex DW Krovar Lucenit Marmer NA 2767 NSC 8950 Seduron Sup r flo Telvar Telvar diuron weed killer UN 2767 Unidron Urox D USAF P-7 USAF XR-42 Vonduron. 

Uses Solvent for chlorinated rubber insecticide and bleach manufacturing paint, varnish and rust remover manufacturing degreasing, cleansing, and drying of metals denaturant for ethyl alcohol preparation of 1,1-dichloroethylene extractant and solvent for oils and fats insecticides weed killer fumigant intermediate in the manufacturing of other chlorinated hydrocarbons herbicide. 

Strong acids include battery acid, murintic acid, and hydrochloric acid. Weak acids include acetic acid, toilet bowl cleaner, and lactic acid. Banned pesticides include Silvex, Mirex, Aldrin, Chlordane, DDT, and Heptachlor. Caustics include oven cleaner and drain cleaner. Flammables include alcohol, acetone, turpentine, lacquer, and paint thinner. Pesticides include rodent poisons, insecticides, weed killer, and other herbicides and fungicides. Pesticide containers should be triple-rinsed, and the contents sprayed on crops or yard, before discarding. 

Examples of the many oxadiazolinones which show herbicidal activity (weed killers) are (118e), (118f), and oxadiazon (118g), which is the subject of many regular reports in the literature. Insecticidal activity is shown by oxadiazolinones (118h), (1181), (the latter is an aphicide), and oxadiazole (117h). 

Throughout this period Avon weed killer, a highly aromatic residue from the Edeleanu process, was about the only oil sold for purely herbicidal purposes. Meanwhile, Diesel oil was becoming popular as an automotive fuel and attempts were being made to improve its quality by removing its aromatic ingredients, a process that decreased its toxicity to plants. 

In 1936 Sinox, a dinitro selective weed killer, was introduced and widely used, not only in cereal crops but in peas, onions, flax, and other important crops. In the early forties a private dealer in the Salinas Valley of California discovered the selective herbicidal use of stove oil in carrot crops. As war conditions made labor scarce and military demands called for increased production, this proved a great boon to the vegetable growers. 

The new and highly specialized petroleum products used as weed killers represent an application to agriculture of products developed by modem petroleum technology. Their increased usage is certain as these herbicides replace more costly means for weed control, in some cases reducing the cost to about one third that of previously known methods. 

Quality control standards have been developed for the new petroleum weed killers and laboratory techniques have been worked out tor testing and establishing the suitability of a given petroleum fraction for a specific herbicidal use. Although attempts to correlate herbicidal action with physical and chemical tests have not been entirely successful, the use of additional specific t ts to determine the chemical composition of the fraction has served as an indicator of toxicity in the specific composition under study. 

Sales of agricultural products were 600 million in 1984. Du Pont expects to double this amount by 1990. There are many new products in the pipeline. Several of these new products are weed killers based on sulfonylurea chemistry. This family of weed killers is characterized by very low toxicity to mammals and high herbicidal activity at very low application rates in the field—often less than an ounce per acre of cropland. 

Mode of Action of the Herbicide DCMU When chloroplasts are treated with 3-(3,4-dichlorophenyl)-l,l-dimethylurea (DCMU, or diuron), a potent herbicide, 02 evolution and photophosphorylation cease. Oxygen evolution, but not photophosphorylation, can be restored by addition of an external electron acceptor, or Hill reagent. How does DCMU act as a weed killer Suggest a location for the inhibitory action of this herbicide in the scheme shown in Figure 19-49. Explain. 

Diuron An herbicide used as a weed killer. Persists in ground water and highly toxic to aquatic invertebrates. 

Herbicides, or weed killers, may be classified as pesticide chemicals. They can kill plants on contact, or they can be translocated (i.e absorbed by one part of the plant and carried to other parts where they exert their primary toxic effect). Most commonly used herbicides have a low toxicity and have caused few adverse effects in users. Some herbicides pose more serious problems to the central nervous system (CNS) and can cause depression. The skin absorption of herbicides also may cause skin irritation, dermatitis, and photosensitization in addition to peripheral motor neuropathies. 

When the American Chemical Society was founded in 1876, no more than half a dozen weed-killers were in use (43). In 1936, 60 years later, that number still remained almost unchanged. There now are over 200 herbicides and other plant growth regulators in common use, but the world requirements for food, fiber, and forest products—the principal beneficiaries of herbicides—never were greater. Still, the public is saying clearly that it must know what happens to all these chemicals and what some of the consequences will be. 

LINUREX LINURON LINURON (herbicide) LOREX LOROX LOROX UNURON WEED KILLER... 

KARMEX KARMEX DIURON HERBICIDE KARMEX DW MARMER SUP RFLO TELVAR TELVAR DIURON WEED KILLER UNIDRON USAF P-7 USAF XR-42 VONDURON... 

Pesticides are chemicals or biological substances used to kill or control pests. They fall into three major classes insecticides, fungicides, and herbicides (or weed killers). There are also rodenticides (for control of vertebrate pests), nematicides (to kill eelworms, etc.), molluscicides (to kill slugs and snails), and acaricides (to kill mites). These chemicals are typically manmade synthetic organic compounds, but there are exceptions which occur naturally that are plant derivatives or naturally occurring inorganic minerals. 

---