Effect of Transplant Age, Tobacco Cultivar, Acibenzolar-S-Methyl, and Imidacloprid on Tomato Spotted Wilt Infection in Flue-Cured Tobacco

Tomato spotted wilt virus (TSWV; family: Bunyaviridae) remains a serious problem in flue-cured tobacco production in Georgia and other parts of the United States. Stand losses in recent years have averaged 30% across the state, with total losses in some fields. There are no commercially available TSWV-resistant cultivars and resistant transgenic tobacco lines that have the TSWV nucleoprotein gene are not accepted by the tobacco industry. Current management strategies may still result in high infection rates. Therefore, other management strategies need to be developed. In many crops, acibenzolar-S-methyl (ASM) has been shown to induce resistance against bacterial, fungal, and viral plant pathogens as well as nematodes. ASM induced resistance in pepper to bacterial spot caused by Xanthomonas axonopodis pv. vesicatoria as early as 3 days after application (16) and significantly increased survival of pepper plants against Phytophthora root and crown rot (10). Studies on the effect of ASM on tomato spotted wilt incidence on tomato and tobacco showed a significant reduction in incidence in combination with other treatments such as reflective mulches and insecticides (12) or with timing of application, such as when applied before transplanting (4,11). Reproduction of the rootknot nematode (Meloidogyne javanica) and the reniform nematode (Rotylenchulus reniformis) was significantly reduced after pineapple plants (Ananas comosus) were treated with ASM (2). Imidacloprid (IMD) is a neonicotinoid insecticide. It has both systemic and contact activity for the control of sucking insects, including thrips. Joost and Riley (6) found that the tobacco thrips (Frankliniella fusca) reduced probing time on plants treated with IMD and preferred to feed on nontreated plants. IMD acts on the insects in two ways, either killing them directly as a nerve toxin or indirectly when insects avoid feeding on treated plants and starve (13). In combination with ASM, it reduces TSWV incidence (4,14). Tobacco growers plant transplants with a range of different ages but prefer to grow older, 10-week-old transplants. Age of plants at the time of infection plays a significant role in the incidence of some viral infections. Sugar beet seedlings were more susceptible to infection with Beet curly top virus and losses were higher than when older plants were infected (19). Also, Lapidot (7) found that seedling age affected resistance of common bean cultivars to Tomato yellow leaf curl virus, with 14day-old plants being nearly 100% susceptible, whereas 26and 12-day-old plants had only 34 and 40% infection, respectively. Mandal et al. (9) found that age of tobacco plants at the time of inoculation with TSWV in the greenhouse had an effect on the development of local lesions and systemic infection. The 14-week-old plants had fewer local lesions per plant and fewer plants developed local lesions compared with 6or 10-week-old plants. Systemic infections were significantly reduced in the 14-week-old plants compared with the 6or 10-week-old plants. The objectives of this study were to determine if transplant age and preplant applications of ASM and IMD influence TSWV incidence, yield, and crop value in flue-cured tobacco.