CARRYOVER OF SOIL-APPLIED HERBICIDES ON FLUE-CURED TOBACCO

Abstract

An outbreak of a tobacco leaf disorder characterized by interveinal chlorosis
of lowermost leaves was recorded for the first time in fields on the Beau
Champ Sugar Estate in October 2003. Given that tobacco is grown on sugar
cane rotational lands, herbicide simulation trials were conducted from 2005
to 2007 at Réduit, Richelieu and Beau Champ to determine whether the
residual effects of one or more of the pre-emergence and post-emergence
herbicides commonly used in sugar cane might be responsible for the
characteristic chlorotic symptoms. On all three sites, symptoms of
interveinal and marginal chlorosis and necrosis of leaves were reproduced
following tobacco transplantation in plots previously sprayed with either
Karmex Flo, Karmex Flo + Velpar, Atrazine + Velpar + Terbo, Tebusan,
Garlon, DCMU or Tebusan + DCMU. Such symptoms could thus be
attributed to carryover of herbicides of the phenylurea (Tebusan, DCMU
and Karmex Flo), pyridine (Garlon) and triazinone (Velpar) families. Since
the carryover effects of these herbicides reduced tobacco yield and quality,
growers are henceforth recommended to avoid fields sprayed with these
herbicides during the last or two-last sugar cane cropping cycles.

Keywords: Flue-cured tobacco, herbicides, interveinal yellowing, leaf
disorder.