SUBSTITUTED PHENOLS 



The dinitro alkyl phenols and chloro substituted phenols have been used widely as 

 contact selective and nonselective post-emergence herbicides. They have also been 

 used for selective pre -emergence weed control in a number of large-seeded crops, 

 including peanuts, soybeans, lima beans, snapbeans, and cotton. The substituted phenols 

 consist mainly of two types. 



(1) Dinitro compounds .-- These include the parent compounds DNBP (dinitro ortho 

 secondary butylphenol), DNAP (dinitro ortho secondary amylphenol), and DNC (dinitro 

 ortho cresol). They are not soluble in water but are soluble in oil and may be applied 

 in an oil carrier, or emulsified with water and applied as an emulsion. The parent 

 compounds are used for pre -emergence and nonselective post-emergence weed con- 

 trol. The salts of these compounds, including sodium, ammoniunn, various amines, and 

 others, are water soluble, and are generally used for selective pre-emergence and 

 post-emergence weed control in some crops. 



The dinitro compounds are yellow dyes which impart a yellow color to clothes and 

 skin. They are poisonous to livestock and humans when taken internally or under con- 

 ditions of sustained contact with the skin. However, they can be used for weed control 

 without danger if precautions are taken to avoid inhaling the vapors or coming in con- 

 tact with the spray drift or spray solution. 



(2) Chloro substituted phenols . --These include PCP (pentachlorophenol), which is 

 soluble in oil but not in water, and its sodium salt (sodium pentachlorophenate), which 

 is soluble in water. PCP is used as a fortifying agent in oil sprays for nonselective 

 weed control. PCP in oil and sodium PCP in water are also used for selective pre- 

 emergence weed control in several crops. 



CARBAMATES 



The carbamates at present include IPC (isopropyl N-phenylcarbamate) and CIPC 

 [isopropyl N-(3-chlorophenyl)carbamate] . They are relatively insoluble in water but 

 are formulated with organic solvents as emulsifiable concentrates. The carbamates 

 form emulsions with water and may be applied as either low- or high-gallonage 

 sprays. Considerable improvement has been made in formulating these products in 

 recent years. They are effective as selective dormant post-emergence sprays for the 

 control of annual grasses, chickweed, and other broadleaved weeds in alfalfa, clovers, 

 and strawberries. CIPC is less volative than IPC and possesses greater residual weed- 

 control properties. It is now being used effectively in some areas for pre-emergence 

 weed control in cotton, soybeans, snapbeans, lima beans, spinach, and certain other 

 field and horticultural crops. The carbamates are also used as pre-planting sprays for 

 weed control in canning peas, strawberries, and sugar beets. 



SUBSTITUTED UREA HERBICIDES 



This new group of herbicides include smonuron [3 -(p-chlorophenyl)- 1,1 -dimethyl - 

 urea], diuron [3-(3,4-dichlorophenyl)- 1, 1-dimethylurea]; and fenuron [3 -(phenyl) - 1, 1- 

 dimethylurea] , previously known as CMU, DCMU, and PDU, respectively. These com- 

 pounds are only slightly soluble in water. They are formulated as wettable powders or 

 as liquids and must be applied as suspensions in high volumes of water. They are the 

 first group of organic chemicals to possess sufficient residual properties to be used 

 as soil sterilants. At present they are being used for nonselective weed control on non- 

 cultivated land. However, diuron and monuron have also shown considerable experi- 

 mental promise and are being used as selective pre-emergence herbicides in cotton, 

 asparagus, and certain other crops. 



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