During the past few years chemicals have been introduced and are in most cases proving effective for weed control in plant beds. The two most widely used are calcium cyanamide and methyl bromide. Allyl alcohol has had limited use. Since these chemicals are now being used, it was decided that an evaluation be made under farm conditions over the East Tennessee Burley Tobacco area to evaluate these materials for weed control, stand of plants, and quality of plants.
Calcium cyanamide is sold in two forms: as a powder under the brand name Aero Cyanamid, and in the granular form as Aero Cyanamid, Granular (13)*. The granular form is the one most used for weed control in tobacco beds and the one used in this work. For simplicity and brevity, the term cyanamid will be used throughout the remaining part of this paper. It is a material that contains 21 per cent nitrogen and kills weed seeds on contact. It is black in color because of the presence of carbon and is distinctly alkaline, due to the presence of lime. One ton of cyanamid has a CaC03 equivalent of 1260 pounds basic (8).
Methyl bromide under pressure or at low temperatures is an odorless clear liquid but it quickly vaporizes at temperatures above 43º F. It disperses rapidly and has remarkable penetrating powers. Its killing action is rapid and it is quickly dissipated after fumigation is completed. The gas is three times as heavy as air. The material used in these investigations is known commercially as Dowfume MC-2 which contains 98 per cent methyl bromide and 2 per cent chloropicrin which acts as a warning agent (3).
Allyl alcohol is a free flowing liquid with a pungent odor and is miscible with water. Allyl alcohol, sold under the brand name of Iscoweed, was used in these investigations (12)
