Postemergence

Up until 1986 the major use for 2-j -butylphenol was in the production of the herbicide, 2-j -butyl-4,6-dinitrophenol [88-85-7] which was used as a pre- and postemergent herbicide and as a defoHant for potatoes (30). The EPA banned its use in October 1986 based on a European study which showed that workers who came in contact with 2-j -butyl-4,6-dinitrophenol experienced an abnormally high rate of reproduction problems. Erance and the Netherlands followed with a ban in 1991. A significant volume of 2-j -butyl-4,6-dinitrophenol is used worldwide as a polymerization inhibitor in the production of styrene where it is added to the reboiler of the styrene distillation tower to prevent the formation of polystyrene (31). OSBP is used in the Par East as the carbamate derivative, 2-j -butylphenyl-Ai-methylcarbamate [3766-81-2] (BPMC) (32). BPMC is an insecticide used against leaf hoppers which affect the rice fields. 

Another significant use of 3-methylphenol is in the production of herbicides and insecticides. 2-/ f2 -Butyl-5-methylphenol is converted to the dinitro acetate derivative, 2-/ f2 -butyl-5-methyl-4,6-dinitrophenyl acetate [2487-01 -6] which is used as both a pre- and postemergent herbicide to control broad leaf weeds (42). Carbamate derivatives of 3-methylphenol based compounds are used as insecticides. The condensation of 3-methylphenol with formaldehyde yields a curable phenoHc resin. Since 3-methylphenol is trifunctional with respect to its reaction with formaldehyde, it is possible to form a thermosetting resin by the reaction of a prepolymer with paraformaldehyde or other suitable formaldehyde sources. 3-Methylphenol is also used in the production of fragrances and flavors. It is reduced with hydrogen under nickel catalysis and the corresponding esters are used as synthetic musk (see Table 3). 

Although the antibacterial and antifungal activities of bialaphos and phosphinothricin were not found to be usehil, the two agents were later used as biodegradeable, relatively nonselective, postemergent herbicides. Glutamine synthetase inhibition is toxic to plants because the enzyme is key to ammonia assimilation. There is some selectivity for individual plant species as shown by the LD for bialaphos ranging from 0.125 to 8.5 kg/ha (301—303). 

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. 

Pyraflufen-ethyl was primarily developed as a cereal herbicide to control a broad spectrum of broadleaf weeds. Pyraflufen-ethyl applied in early postemergence at 12 g a.i. ha provides excellent control of some important weeds such as Anthemis arvensis, Lamium purpureum and Sinapis arvensis and good suppression of Matricaria chamomilla, Stel-iaria media, Veronica persica and Viola spp. 

Application methods Usually as water spray or in liquid fertilizers applied preemergence, but also may be applied preplant or postemergence. Rates of 2-4 pounds/acre (2.24-4.48 kg/ha) are effective for most situations higher rates are used for nonselective weed control, and on high organic soils... 

It is estimated that over 100,000 acres in Hawaii and some 250,000 acres in Louisiana each year are treated with herbicides, mostly 2,4-D and TCA (sodium salt of trichloroacetic acid), for pre- and postemergence weed control. Johnson grass on ditch banks on some 50,000 to 75,000 superficial acres in Louisiana is controlled with sodium chlorate or TCA. Some trials with CMU [3-(p-chlorophenyl)-l,l-di-methylurea] are in process. Florida cane growers use 150,000 pounds of 2,4-D amine salt of Karmex W on 43,000 acres of cane and anticipate using up to 100,000 pounds per year. Of the growers in Puerto Rico, 60% are said to use herbicides as either pre- or post-emergence sprays. 

Dicamba (3,6-dichloro-2-methoxybenzoic acid) is primarily used as a postemergence broadleaf herbicide, which interferes with normal plant auxin function, subsequently causing uncontrolled growth and the inhibition of the phototropic and geotropic function. Cumulative response results in plant death. The success of auxinic analogues such as Dicamba and 2,4-dichloropheno-xyacetic acid in weed control has led to widespread manufacturing and use. Estimated U.S. production for Dicamba was 5 million kg in 1990 [391]. 

S-ethyl-N,N-dipropylthiocarbamate org chem C ffi NOS An amber liquid soluble In water at 370 parts per million used as a pre- and postemergence herbicide on vegetable crops. Abbreviated EDTC. ( es eth-3l en en dT pro p3l,thT-o kar-b3,mat ... 

Bentazone Acid 25057-89-0 2.55 1972 Herbicide A postemergence herbicide used for selective control of broadleaf weeds and sedges (a weed) in beans, rice, com, peanuts, mint, and others... 

Mecoprop Acid 7085-19-0 2.29 -1956 Herbicide A postemergence herbicide used to control broad-leaved weeds such as cleavers, chickweed, plantains, and clover... 

Propanil Anilide 709-98-8 0.42 1961 Herbicide A postemergence herbicide used for broad-leaved and annual grass weed control in rice and other crops... 

Linuron Phenylurea 330-55-2 2.03 -1965 Herbicide A herbicide for the pre- and postemergence control of annual grass and broadleaved weeds... 

Atrazine Triazine 1912-24-9 3.75 1957 Herbicide A triazine herbicide used pre- and postemergence with restricted permitted uses to control broad-leaved weeds and grasses... 

The sulfonylureas described here are new herbicides with unprecedented activity. Activity at extraordinarily low rates of application has been demonstrated by both preemergence and postemergence applications (Ref. 1). These rates are best describee in grams per hectare compared to kilograms per hectare for most herbicides currently marketed. Furthermore, the combination of low application rates, half lives of generally less than two months in the soil (Ref. 2) and excellent safety to mammals [LD5o s of generally >5000 mg/kg for technical material in male rats] (Ref. IC) makes these compounds attractive products from an environmental viewpoint. 

Comparison of AC 222,293 with its Optical and Positional Isomers Postemergence Test - Rates in Kg/Ha... 

From the earliest greenhouse studies, it was obvious that AC 252,214 was an interesting compound. Remarkably, it was well tolerated by legumes, especially soybeans, yet showed a broad-spectrum of herbicidal activity, killing broad-leaved, grassy and perennial weeds. Further it was shown that AC 252,214 could be used both as a preemergent and postemergent herbicide. Rates for field application are 125-250 g/ha (12). 

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