SUGGESTED GUIDE FOR CHEMICAL CONTROL OF WEEDS' 



Herbicides are efficient and economical weed-control tools for many weed-crop 

 situations. However, they are precision tools which require the best and latest in- 

 formation available for successful use. 



Chemicals still cannot be used for the control of all weeds in every crop. But through 

 research an increasing number of herbicides are being made available, and the specific 

 situations in which each is most effective are being determined. As selective herbicides 

 come into wider use in crop production, better harvesting methods, a greater degree of 

 mechanization, better yields, and fewer losses will prevail. 



Chemical weed control should be considered as a supplement to the use of improved 

 cultural practices. Good clean seed is a sound starting point for any weed-control pro- 

 gram. Thorough tillage and seedbed preparation, followed by clean, efficient, shallow, 

 timely cultivation is extremely important. Moreover, there are no substitutes for 

 proper fertilization and management of adapted species, varieties, or hybrids of crop 

 plants. 



I. CHEMICALS USED FOR WEED CONTROL 



Many herbicides are being used for weed control, and many others are being 

 evaluated experimentally to determine their usefulness. Only those of current general 

 interest and usefulness are described in this report. , 



PHENOXY COMPOUNDS 



Several compounds in this group, including 2,4-D (2,4-dichlorophenoxyacetic acid), 

 2,4,5-T (2,4,5-trichlorophenoxyacetic acid), MCPA (2-methyl, 4-chlorophenoxyacetic 

 acid), and 2-(2,4,5-TP) (2,4,5-trichlorophenoxypropionic acid) are variously used as 

 post-emergence selective herbicides to control broadleaved weeds in corn, small 

 grains, sorghum, rice, flax, lawns, and brush and weeds in pastures, along roadsides, 

 rights-of-way, and drainage ditches. Some of the phenoxy compounds may also be 

 applied to the surface of the soil as a pre -emergence treatment to control grasses and 

 broadleaved weeds in corn and other crops. 



Phenoxy compounds are usually formulated and marketed as two basic types. 

 1. Salts 



The most widely used salts of 2,4-D, MCPA, 2,4,5-T, and other phenoxy acids in- 

 clude such organic annine salts as diethanolamine, triethanolamine, alkanolamine, 

 dimethylamine, triethylamine, isopropylamine, and others. These organic amine salt 

 formulations are available chiefly as water-soluble liquids, but water-soluble powder 

 formulations of some of these phenoxy compounds are also available for commercial 

 use. The amine salt formulations are more phytotoxic per pound of acid equivalent 

 than the other salt forms, and are more effective in controlling a wider range of weeds. 



The technical information in this publication was compiled and reviewed by W. C. 

 Shaw, F. L. Timmons, W. B. Ennis, Jr., D. L. Klingman, R. J. Aldrich, and M. W. 

 Parker of the Field Crops Research Branch, Agricultural Research Service. 



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