Later generations feed after harvest on non-commercial suckers. Severe damage most commonly occurs during late July and August. There are a number of natural enemies that help control hornworm populations, with two having been used in augmentative biological control programmes - the braconid Cotesia congregata, and the bacterium Bacillus sphingidis.Įarly generations are potentially damaging to marketable tobacco in the southern USA, sometimes stripping entire plantations. sexta remained below the economic threshold for the duration of the trial ( Warren et al., 1992). sexta in the USA ( Johnson, 1996).įield evaluation in North Carolina of a transgenic tobacco cultivar containing a Bacillus thuringiensis insecticidal protein gene demonstrated that damage by M.
Additionally, certain cultivars of tobacco have been found to be resistant to M. Early planted tobacco, correct (not excessive) nitrogen fertilization, sucker control, stalk destruction, and autumn ploughing all help to reduce overwintering populations ( Reagan et al., 1978). In the southern USA it is recommended that hornworms on tobacco be treated with insecticides when infestation levels exceed the economic threshold of five or more large (2.5 cm or longer), unparasitized larvae, per 50 plants ( North Carolina State University, 1998).Ĭultural practices are very important. Malathion, diazinon, carbaryl and fenitrothion have been used with great effect.
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