Developing a Fruit Injury Based Action Threshold for Bollworms and Field Validation

Friday, January 6, 2017: 8:45 AM
Pegasus A (Hyatt Regency Dallas)
David Kerns , Texas A&M University
Sebe Brown , LSU AgCenter
Fei Yang , LSU Agcenter
Scott D. Stewart , The University of Tennessee
Gus Lorenz , The University of Arkansas
Nick Seiter , University of Arkansas System Division of Agriculture
Glenn Studebaker , University of Arkansas
Jeff Gore , Mississippi State University
Don Cook , Mississippi State University
Angus Catchot , Mississippi State University
Since the introduction of Bt cotton in the United States in 1996, management of the Heliothines including the bollworm, Helicoverpa zea, has become much less problematic.  However, there are still incidents where unacceptable fruit injury is experienced and insecticidal oversprays are utilized to prevent yield loss.  There has been much speculation surrounding the reasons for control failures among Bt cotton technologies including Bt resistance or tolerance, inadequate expression of Bt toxins expression due to plant phenology or environmental stressors.  The objective of this project was to determine economic injury levels and an economic threshold across Bt technologies based on fruit injury, and to validate that threshold the following year. Economic injury levels varied from 3.54-14.76% injured fruit depending on crop value, yield potential and control cost. On average, across varied crop values and yield potential, the economic threshold was approximately 6% injured fruit based on cotton with a yield potential of 1,200 lbs-lint/ac, a crop value of $0.70/lbs-lint with a control cost set at $24/acre. This estimate falls within the range of most current state extension recommendations. Using a 6% injury economic threshold relative to preventative sprays or no insecticide applications, this threshold appears to offer reasonable protection from unacceptable bollworm injury.