Chemical topping of burley tobacco

Topping tobacco (Nicotiana tabacum L.) is a procedure that requires the removal of the terminal bud or inflorescence of the plant. Topping tobacco has been a common practice almost since tobacco has been domestically cultivated, due to the desirable effect it has on yield and quality of the tobacco leaf. The objective of this study was to determine if burley tobacco can be chemically topped using common sucker control materials. The burley tobacco variety TN 86 and the non-flowering burley tobacco breeding line BM 16 were used in the research study. Four chemical topping treatments were applied to both burley tobacco lines. These included: KMH; KMH tank mixed with flumetralin (KMH/P+); FST7 tank mixed with flumetralin (FST7/P+); and FST7, followed one week later with a treatment of flumetralin (FST7-P+). These treatments were applied at three different plant growth stages. Chemical treatments were applied at either the 25, 50, or 75 percent button stage for TN 86 and either the 25, 30, or 35 leaf stage of maturity for BM 16. The most effective chemical topping for TN 86 occurred when chemical treatments were applied at the 25 percent button growth stage. Applications at later maturity stages resulted in less effective chemical topping. Compared to the hand topped check, all the chemical topping treatments resulted in reduced yields. Although the most effective topping was achieved at the 25 percent button maturity stage, application of chemicals at this stage resulted in the largest yield reduction. This yield reduction was due to reduced leaf size, which lowered cured leaf weight in the upper portion of the plant. For BM 16, excellent topping was obtained with all of the chemical treatments, regardless of the growth stage at which they were applied. In comparison to the hand topped check, yields of BM 16 were reduced by all chemical treatments when applied at the 25 leaf stage of maturity; however all treatments applied at the 35 leaf stage resulted in increased yields. Although the size of at least the top three leaves of the plant were reduced, regardless of chemical treatment or time of application, yields of BM 16 increased due to the higher number of harvestable leaves.