48th TWC, Tob. Work. Conf., 2018, abstr. 06

Evaluation of transplant water and foliar applications of boron to dark tobacco

University of Kentucky, Princeton KY USA

Boron deficiency has been documented on several farms in the dark tobacco production area of Kentucky and Tennessee USA. Typical symptoms of boron deficiency include leaf breakage approximately 2 inches from the stalk and possibly stunting/yellowing/malformation of the terminal bud. High soil pH has also been a contributing factor as boron becomes less available as soil pH approaches 7 or higher. Field experiments were conducted in 2014, 2015, and 2016 at a private farm near Mayfield KY where boron deficiency had been documented on the tobacco crop in 2012 and the soybean crop that followed in 2013. Treatments included transplant water-simulated (TPW) applications of boron made immediately after transplanting, or foliar applications made at 3 to 4 weeks after transplanting. Boron rates used at either application timing were 0.25, 0.5, or 1.0 lb B per acre. Boron source was boric acid (Borosol® liquid, 10% B). In 2014, extensive transplant injury was seen from 0.5 and 1.0 lb B/A applied as TPW applications. Injury resulted in 34 to 66% injury from boron at 0.5 to 1.0 lb B/A, respectively, and as much as 29% stand loss at the 1 lb B/A rate. However, foliar boron applications were beneficial, with tobacco showing increasing positive visual growth responses to increasing rates of boron. 2014 yields were reflective of negative responses seen to TPW applications and positive responses seen to foliar applications. In 2015 and 2016, injury from TPW applications was not obvious as it was in 2014, presumably due to much wetter conditions during and following transplanting and possibly higher soil pH in 2014. Growth and yield responses in 2015 and 2016 were also less than those seen in 2014. The 2016 experiment also showed that TPW and foliar boron applications increased boron levels above critical levels (25 ppm) in plant tissue. (Reprinted with permission)