Tomato Spotted Wilt Virus: TSWV in Vegetable Crops: Tospoviruses

Tospoviruses In Solanaceae and Other Crops in The Coastal Plain of Georgia

Tomato Spotted Wilt Virus in Tobacco

Alex Csinos

Studies conducted in 1999 and 2000 at four locations each year established the use, rate and efficacy of imidacloprid and acibenzolar-S-methyl to effectively manage TSWV in tobacco (Csinos et al., 2001). Those results have been confirmed in Georgia, South Carolina and North Carolina.

Current label recommendations for use of imidacloprid are 1.0-2.8 oz. of formulation (Admire 2F) per 1,000 plants applied as a tray drench, washed into the root ball 3-7 days before transplanting (Cooperative Extension Service). Recommendations for the use of acibenzolar-S-methyl (Actigard 50 WP) are variable depending on if plants are produced in field plant beds or in floats. In general 0.5 oz. of Actigard 50 WP will treat 32,000-50,000 plants. Treatment should be made 5-7 days prior to transplanting.

Some growth delays and phytotoxicity may be observed with the application of Actigard. Young and tender plants tend to be more affected than older, hardened off plants. Drought, very hot weather, wind damage, chemical injury, or any other stresses to the plants may increase phytotoxicity. Plants should be transplanted as fresh as possible. However, plants stunted due to Actigard treatment generally recover. Admire or Actigard applied alone provides 20-30 percent control. However, the use of both materials in the greenhouse prior to transplanting can provide 40-60 percent control, the additive sum of the two treatments if they were used alone.

Tobacco cultivars do not have appreciable resistance to TSWV and cultivar selection is not recommended in management of the disease. However, some studies have demonstrated that NC 71 tends to be less susceptible to TSWV than K-326.

Figure 9. Area under the disease curve (AUDPC) for cumulative symptomatic TSWV tobacco treated with acibenzolar-S-methyl, imidicloprid and combinations. A: Blackshank Farm; B: Blackshank nursery; C: Entomology site; D: Bowen Farm. Curves (areas) followed by the same letter(s) are not significantly different from each other, P=0.05.

(Actigard 50 WP)

Acibenzolar-S-methyl is a plant activator that induces a plant’s defense mechanism(s) and has been shown to have antifungal, antibacterial (Cole, 1999) and antiviral activity across several different plant species (Pappu et al., 2000). Solanaceous crops appear to be most sensitive to activation by Actigard and thus show the highest subsequent systemic acquired resistance. Activity on TSWV was first recognized in 1997.

(Admire 2F)

Imidacloprid reduces transmission of the virus from the thrips to the host plant. Application of imidacloprid by transplant drench to the root system results in less TSWV infection, but a foliar application of imidacloprid does not provide protection from TSWV. The primary mode of action is through antifeeding activities of thrips, and this antifeeding only occurs if the imidacloprid is applied to the roots and the insecticide distributed systemically through the plant. Both transplant drenches and transplant water treatments reduce TSWV (Jones et al., 1998; Bertrand et al., 1998).

Figure 10. AUDPC for cumulative enzyme-linked immunosorbent assay (ELISA) positive samples. A: Blackshank Farm; B: Blackshank nursery; C: Entomology site; D: Bowen Farm. Curves (areas) followed by the same letter(s) are not significantly different from each other, P=0.05.

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