Progress 07/01/04 to 06/30/05
Outputs
Tobacco budworms, Heliothis virescens (F)., were the number one insect pest of Georgia's flue-cured tobacco in 2004, costing producers nearly $2 million in costs of control and damage. Budworms have been the number one tobacco insect pest in 8 of the past 10 seasons, and many Georgia growrs apply 2-3 applications of insecticides each year to prevent economic losses to their tobacco crop. Lambda cyhalothrin, a pyrethroid insecticide, was labeled in 2003 for use on tobacco for controlling tobacco budworms and tobacco hornworms. Results from field trials in 2003 indicated poor control with this product in some areas of the state. Thus, toxicology studies, were initiated in 2004 to document the differences in susceptibility of tobacco budworms to lambda cyhalothrin and other pyrethroid insecticides. The effective dose that caused 50% moribund larvae (ED50) for the standard organophosphate insecticide acephate was elevated some at the Mitchell, Terrell, and Tift County
sites evaluated in 2004. Although the acephate responses were actually higher in 2004 than in any other year of the monitoring; the rates were only slightly higher than the baseline values obtained in 1983 (35 micro g per g larval weight), the first year that acephate was monitored for resistance. Responses for methomyl, another standard carbamate insecticide, were about the same as in previous years, with Terrell County down a little and Tift County up a little from the historical average. The ED50's for cyhalothrin were 10x and 4x higher in Terrell and Tift Counties in 2004 compared to the long term average of 0.06 micro g per g larval weight, respectively. This indicates that resistance may be developing to cyhalothrin in these locations. The ED50 responses to cypermethrin, another pyrethroid insecticide, also were alarming for Terrell and Tift Counties, 8x and 7x higher than the long term average of 0.78 micro g per g larval weight. These results indicate that pyrethroid
resistance has apparently developed in Georgia, and budworm control with recommended insecticides needs to be carefully monitored in the coming years..
Impacts
This project has demonstrated the onset of pyrethroid insecticide resistance in tobacco budworms, the most costly insect pest on Georgia's tobacco crop. Growers will be advised to select other classes of insecticides than the newly labeled pyrethroids to treat for budworm infestations when chemical controls are needed.
Publications
- McPherson, R. M., N. Roberson, and D. Taylor. 2005. Tobacco budworm and hornworm control with foliar applications of insecticides. 2004 Georgia Tobacco Research-Extension Report. Coop. Res.-Ext. Publ. 1-2005: 47-50.
- McPherson, R. M., N. J. Roberson, and J. D. Taylor. 2005. Tobacco budworm and hornworm control on flue-cured tobacco in Georgia, 2004. Arthropod Management Tests 30: F86 (2pp).
- McPherson, R. M. and D. C. Jones. 2005. Insect losses in 2004. 2004 Georgia Tobacco Research-Extension Report. Coop. Res.-Ext. Publ. 1-2005:3.
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