Pre-emergent

DichlorobenzotrifIuoride. This dichloro compound is produced from 2,4-dichloroben2otrichloride and hydrogen fluoride. One commercial appHcation is the manufacture of the pre-emergent herbicide, dinitramine [29091 -05-2]. 

Phenylcarbamates. Phenylcarbamate herbicides represent one of two subgroups of carbamate herbicides, the phenylcarbamates and the thiocarbamates (299). Both groups are prone to volatilization losses the thiocarbamates are particularly susceptible and should be sod-incorporated immediately after apphcation (2). The carbamate herbicides are used, in general, for the selective pre-emergence control of grass and broadleaved weeds (299). Exceptions would include barban, desmedipham, and phenmedipham which are appHed post-emergence. 

Triazines. Triazine herbicides are one of several herbicide groups that are heterocycHc nitrogen derivatives. Triazine herbicides include the chloro-, methylthio-, and methoxytriazines. They are used for the selective pre-emergence control and early post-emergence control of seedling grass and broadleaved weeds in cropland (299). In addition, some of the triazines, particularly atrazine, prometon [1610-18-0] and simazine [122-34-9] are used for the nonselective control of vegetation in noncropland (2). Simazine may be used for selective control of aquatic weeds (2). 

Miscellaneous Trifluoromethyl Compounds. The herbicides in this group are used for a wide variety of weed-control purposes. Acifluorfen, lactofen [77501-63-4] and oxyfluorfen are used for selective, pre-, and post-emergence weed control in croplands. Fluorochloridone is used for selective, pre-emergence weed control in cropland, and fluridone, fomesafen, and mefluidide [53780-34-0] are used for post-emergence control (296). Fluridone is also used as an aquatic herbicide (2). 

Cinmethylin and cloma2one [81777-89-1] are used for selective pre-emergence control and etholumesate [26225-79-6] for selective pre- and post-emergence weed control (2,296). 

Chlorine adds to ketene to form chloroacetyl chloride [79-04-9] (78). Chloroacetyl chloride (CAC) is used in large volume in the manufacture of the pre-emergence herbicides alachlor [15972-60-8] and butachlor [23184-66-9]. It is estimated that the CAC requirement for this appHcation was in excess of 45,000 metric tons in 1992. Significant volumes of CAC are also used in pharmaceutical manufacture, such as anesthetics of the Hdocaine type, and in the production of the tear gas chloroacetophenone [532-27-4]. Other commercial methods for the manufacture of CAC have been described (79). 

In addition to the use of 2,4-dichlorophenol in the synthesis of 2,4-D herbicides (acid 2,4-D, acid 2,4-DP, acid 2,4-DB), it is also found in the selective post-emergence herbicide, diclofop-methyl [51338-27-3] (61) and as a selective pre-emergence herbicide, oxadia2on [19666-30-9] (62). A postemergence herbicide is appHed between the emergence of a seedling and the maturity of a crop plant. 

You should be familiar with various occupancies and locations in your community where hazardous materials are used, stored, transported, or produced. To accomplish this familiarization, you must complete pre-emergency planning and inspection activities. 

Pre-Emergency Plan," Industrial Risk Insurers, Hartford, CT, Februtiry 1981. 

C 2.41 X 10 mm Hg at 22.0°C 1.8mgL in water at 25°C Soluble in polar organic solvents Unstable in acidic, neutral and basic aqueous solutions Flumioxazin provides pre-emergence control of susceptible weeds in crops. Flumioxazin may also be used as part of an early preplant burn-down program in various crops... 

Use pattern Orbencarb is a systemic pre-emergence herbicide to control most annual grasses and broad-leaved weeds... 

Sulfentrazone is a broad-spectrum, pre-emergent herbicide that provides good control over broadleaf weeds, grasses and sedges in crops and turf. The metabolism of sulfentrazone in animals and plants is similar. The major plant metabolite of sulfentrazone is 3-hydroxymethyl sulfentrazone (HMS). The soybean tolerance of 0.05 mg kg includes residues of sulfentrazone plus its major metabolite, HMS. The rotational crop tolerance includes residues of sulfentrazone and its major metabolites, HMS and... 

For compounds applied to annual crops, another approach is to apply the compound to bare soil prior to crop emergence and follow the soil dissipation of the compound as the crop emerges and grows throughout its normal growing season.This is the appropriate use pattern for pre-emergence compounds and represents another approach that may used to study the soil dissipation of foliar-applied compounds. 

Dacthal is a widely used pre-emergent herbicide that is applied to many crops for the control of annual weeds. Dacthal is typically applied to agricultural soils at 6-14kg ha [214], In the soil environment, Dacthal transforms to mono- and diacid-metabolites that are more water soluble than the parent herbicide [215-217]. In eastern Oregon, where Dacthal is applied to onions, the diacid metabolite is the principal form of Dacthal detected in groundwater obtained from domestic wells [218, 219],... 

One of the major problems in rice production is grass control. Various grasses compete with rice and drastically reduce yields. Results of preliminary experiments in Venezuela (9) indicate that rice yields may be increased by the application of dinitrophenol as a pre-emergence herbicide, even though rice stands are reduced by this chemical. Additional research is needed in this field, as the possibility exists... 

Rice. Rice, a major food crop in the tropics, is highly resistant to 2,4-D at most periods of growth. Although chemical weed control is widely used in the United States, relatively little has been done in the tropics. Some chemical weed control in rice has begun in Cuba (18), Philippines (39), Malaya (6), and Venezuela (16). Both dinitrophenol and pentachlorophenol were effective as pre-emergence treatments in Venezuela, and CMU gave very promising preliminary results. 

Other Tropical Crops. Herbicides have also been used on a small scale on a number of other tropical crops—for example, 2,4-D and 2,4,5-T have been used in pastures (9, 56). In establishing lawns of Manila grass (Zoysia matrella [L.] Merr.) at the station in Puerto Rico, pre-emergence application of 2,4-D materially... 

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