Chemical control of suckers in dark tobacco

A tobacco plant, like other angiosperms, subtends a bud in its leaf axil. It also possesses accessory buds which, together with the primary bud, are kept in check by apical dominance. In the growing of tobacco, a multiple of cultural operations are performed at various stages of the crop growth directed towards the ultimate production of high yields of desirable quality leaf. Topping is one of such operations. Its purpose is to redirect all the energies of the plant towards better development of the leaf which would otherwise be utilized in the production of fruit and seed. Following topping, or the removal of apical dominance, the axillary buds begin to grow into suckers, The primary suckers in the top three to five leaves elongate and develop rapidly. The purpose of topping is not accomplished to any great extent if these suckers are allowed to grow; therefore, they are usually removed when three to five inches in length, then the top suckers are removed, a source of suppression of suckers further down the stalk is also removed, thus allowing the growth of primary suckers in the lower part of the plant and of secondary suckers in the upper part. Generally, the removal of secondary suckers tears off the tertiary sucker bud tissue with it, but sometimes this tissue remains intact and develops into a tertiary sucker. Removing suckers by hand requires many hours of labor per acre. Dark air cured and fire cured tobaccos are usually topped low, leaving 12 to 14 leaves per plant. The purpose of this low topping is to produce a dark, heavy, oily and relatively thick leaf of large size. The early and low topping of dark tobacco make suckering a difficult and high labor requiring task. An acre of the above type of tobacco may have 125,000 or more suckers, all of which must be removed to obtain optimum yields and quality. Chemicals with either growth inhibiting or contact killing properties are used to control sucker growth. Although many of the chemicals reduce sucker growth to a certain degree, they may damage the plant in one or more ways, thereby lowering the yield or quality of the leaf. Some of these chemicals are now in use in the tobacco producing areas. No chemical has yet been found which would satisfactorily control suckers without damaging the plant or affecting leaf quality. The purpose of this study was to evaluate a variety of experimental preparations and some chemicals already on the market by studying their performance on dark air cured and fire cured tobaccos. The experiments were conducted in cooperation with the Regional Tobacco Sucker Control Committee. Most of the experimental chemicals were provided by the Crop Research Division of the United States Department of Agriculture.