Postemergent herbicides

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. 

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... 

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). 

Chemicals such as simazine are used alone as herbicides, or more often in combination with other herbicides such as oxyfluorfen, oryzalin, or norflurazon, generally in four- to six-foot (1.2-2.0 meter (m)) strips down the tree row. The centers are either tilled or mowed parallel with the tree row. In order for strip chemical treatment to be successful, it is essential to eradicate perennial weeds by the use of repeated postemergence herbicide applications and tillage. 

---