|Mullinix, JR., B - UNIVERSITY OF GEORGIA|
Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 9, 2004
Publication Date: October 1, 2004
Citation: Tillman, P.G., Mullinix, Jr., B.G. 2004. Grain sorghum as a trap crop for corn earworm (Lepidoptera: Noctuidae) in cotton. Environmental Entomology. 33(5):1371-1380. Interpretive Summary: Populations of corn earworms can reach economically damaging levels in cotton. Trap crop strategies have proven themselves highly effective on tough pests in agricultural crops in recent years and offer the potential to minimize or eliminate the use of insecticides and preserve natural enemies that control pests. The idea is simple, intercept the insect with a plant that is more attractive to the pest than the main crop. Thus, a 3-year on-farm study was designed to evaluate grain sorghum as a trap crop for the corn earworm. Number of plants with corn earworm eggs was much higher in the grain sorghum trap crop than in the cotton for all three years demonstrating that CEW moths preferred to lay eggs in the grain sorghum trap crop over cotton. The grain sorghum trap crop also helped reduce the need for insecticide applications for this pest for two seasons and enhanced the effectiveness of the parasitoid species for at least one year. We conclude that grain sorghum served as an effective trap crop for the CEW in cotton.
Technical Abstract: This 3-year on-farm study was designed to evaluate grain sorghum, (Sorghum bicolor (L.) Moench), as a trap crop for the corn earworm (CEW), Helicoverpa zea (Boddie). Specifically, the attractiveness of grain sorghum as an ovipositional site and the impact of the trap crop on Trichogramma pretiosum Riley and Orius insidiosus (Say), two natural enemies of CEW in sorghum and cotton, were examined. In 2000, treatments included a grain sorghum trap crop in the center of half of a cotton field, treated cotton (half of the cotton field with the trap crop), and control cotton (the other half of the cotton field without the trap crop). In 2001 and 2002, treatments included a strip of grain sorghum and cotton trap crops along the edge of a cotton field adjacent to a corn field, treated cotton (cotton field associated with these trap crops), and control cotton (cotton field without trap crops). Number of CEW eggs per plant and number of plants with CEW eggs were much higher in the grain sorghum trap crop than in the cotton trap crop, treated cotton and control cotton for all three years demonstrating that CEW moths preferred to oviposit in the grain sorghum trap crop over cotton. An economic threshold of 5% CEW young (1st and 2nd instars) was exceeded more times for control cotton than for treated cotton except in 2000 where sorghum occurred in the center of the cotton field. Thus, for two seasons the grain sorghum trap crops helped reduce the need for insecticide applications for this pest. More plants with CEW eggs were found in control fields compared to treated fields indicating that the grain sorghum trap crop was not the source of CEW. Also, the grain sorghum trap crop was not a sink for the natural enemies T. pretiosum and O. insidiosus, and may have enhanced the effectiveness of the parasitoid species for one year. We conclude that grain sorghum could serve as an effective trap crop for the CEW in cotton.