Control of weeds is an agricultural problem of great importance. For centuries, only salts, ashes, or mechanical means of eradication such as hoeing, cutting, or burning were used in weed control. A large number of chemicals have been used for this purpose also. With the advent of modern railroads, highways, and power lines, the demand has grown for newer and more effective control of weeds and brush. The initial application of chemical herbicides produced erratic results in many instances. Some herbicides retarded the growth rate of certain forms of vegetation but left other forms unaffected. Likewise, some herbicides killed the entire plant, while others killed only the portion sprayed. Since 19ul, however, the discovery of synthetic growth regulating substances or plant hormones as effective weedkillers has brought about a revolutionary change in the chemical control of weeds. The synthetic hormone substances are greatly superior to ordinary chemicals in that they are highly selective as between plant species and have many other additional advantages. They are now being used in many places throughout the world, but too often with little accurate knowledge of their nature or of the special circumstances under which they should and should not be used. Such information is important because these substances can be very destructive to vegetation when improperly applied. Maleic acid hydrazide is a relatively new herbicide, possessing the hormone—like property of retarding plant growth for long periods of time by preventing the division of cell nuclei. Field applications of the hydrazide have shown good growth retarding ability on many types of weed and shrubs In view of the wide variation in environmental conditions and farming practices in different parts of the world, as well as the great variety of crop and weed plants involved, the control of weeds is essentially a local problem, and instructions for specific regions and for specific purposes cannot be given until results of local tests become available. It is therefore necessary to rely on experimental work conducted locally for information on how to use these substances. / Master of Science