Interference and postemergence control of annual grasses in burley and dark fire-cured tobaccos

Interference studies with annual grasses were conducted in 1982 and 1983 in burley and dark fire-cured tobaccos (Nicotiana tabacum L.) at Greeneville and Springfield, Tennessee, respectively. Treatments consisted of annual grass-free periods of 2, 4, 6, 8, and 10 weeks from transplanting and 2, 4, 6, 8, and 10 weeks of interference followed by removal of all weeds and maintenance of weed-free conditions. A season long annual grass-free treatment and a season long annual grass-infested treatment served as controls. Annual grass-free periods were established and maintained by hand-hoeing. In 1982, the critical annual grass-free period and critical duration of interference of annual grasses for Federal grade and yield of burley tobacco and total cured plant and leaf yields of dark fire-cured tobacco were between 4 and 5 weeks after transplanting. Due to dry growing conditions and low annual grass populations yield responses in 1983 failed to indicate critical periods.

Separate studies were conducted in 1982 and 1983 at the same locations to evaluate and compare the performance of sethoxydim {2-[1- (ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen- 1-one} alone and with a crop oil concentrate and fluazifop-butyl {(±)-butyl 2-[4-[(5-(triflouromethyl)-2-pyridinyl)oxy]phenoxy]propanoate} plus a crop oil concentrate for control of annual grasses and tobacco response. They were compared to conventional cultivation and a widely used preplant incorporated treatment of pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine]. The above treatments were applied alone and in combination with acephate.

In 1982, the postemergence herbicides controlled annual grasses as well or better than cultivation or pendimethalin. Tobacco treated with the postemergence herbicides produced yields equal to or less than tobacco treated with pendimethalin. Dark fire-cured tobacco treated with the postemergence herbicides yielded less than did tobacco in the cultivated checks. In 1983, all treatments produced good tobacco yields. Plants from plots treated with sethoxydim applied without a crop oil concentrate produced the lowest dark fire-cured tobacco yields. Acephate in combination with annual grass control treatments did not appear to enhance tobacco growth or yield. Some crystallization of acephate occurred when tank-mixed with sethoxydim and fluazifop-butyl.